Conservation And Recycling of Resources: New Research

CONSERVATION AND RECYCLING OF RESOURCES: NEW RESEARCH

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CONSERVATION AND RECYLING OF RESOURCES: NEW RESEARCH

CHRISTIAN V. LOEFFE EDITOR

Nova Science Publishers, Inc. New York

Copyright © 2006 by Nova Science Publishers, Inc.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Conservation and recycling of resources : new research / Christian V. Loeffe (editor). p. cm. Includes index. ISBN 978-1-60876-513-3 (E-Book) 1. Recycling (Waste, etc.) 2. Conservation of natural resources. I. Loeffe, Christian V. TD794.5.C664 2006 628.4'458--dc22 2006008429

Published by Nova Science Publishers, Inc. New York

CONTENTS Preface

vii

Chapter 1

An Overview of Recent Advances and Trends in Plastic Recyling Sati Manrich and Amélia S. F. Santos

Chapter 2

The Consequences of the Use of Platinum in New Technologies on its Availability and on Other Metals Cycles Ayman Elshkaki and Ester van der Voet

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Index

Vegetation Recovery after Environmental Damage by Metallurgic Industry in the Arctic Region: Transformation of Soil Chemistry in Restored Land Ryunosuke Kikuchi and Tamara T. Gorbacheva

1

61

93

Solid Waste Management, Recent Trends and Current Practices for Secondary Processing of Zinc and Lead Industries in India Archana Agrawal and K. K. Sahu

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Recycling of Wastes (Agricultural Residues and Used Tires) for Activated Carbon Production A. A. Zabaniotou

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Energy Recovery from Waste Incineration: Linking the Systems of Energy and Waste Management Kristina Holmgren

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Artificial Aggregate Made by Cementitious Granulation of Waste Incinerator Fly Ash R. Cioffi, F. Colangelo, F. Montagnaro and L. Santoro

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The Chemical Properties of Municipal Solid Waste Incinerator Ashes and the Effects of Their Utilization as Landfill Cover on Landfill Biostabilization Huang-Mu Lo, Min-Hsin Liu, Chao-Yang Lin, Wen-Fung Liu, Tzu-Yi Pai, Chun-Hsiung Hung, Pin-Hung Cheng, Yuan-Lung Liao, Tsu-Ying Fu and Chao-Chan Yang

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PREFACE The preservation and careful management of the environment and of natural resources and recycling or the processing of used or abandoned materials for use in creating new products must become key parts of the equation for the Earth’s continued sustainable development. At the present time, most developed countries are massively wasteful throughout almost all sectors of the economy ranging from energy use to consumer lifestyles. One of the main obstacles to conservation and recycling of resources is the lack in most countries of national mindsets encouraging such practices as well as the infrastructures to support their carrying out. This new book presents important research in this frontal field. Since the discovery of plastics several decades ago, the widespread consumption of plastic products and their subsequent inappropriate disposal and accumulation have recently generated new societal concerns of waste management due to their inherent slow degradability, high volume increase and low recycling rates, which are negative on the basis of self-sustainability. Regulations imposing waste reduction, reuse and recycling indices and responsibilities, as well as effective collecting system and the development of new, environmentally clean recycling technologies are some of the efforts to achieve the selfsustainability goals. The efficiency of the collection and sorting systems impacts directly on the amount of recycled plastics and on their cleanness and quality, therefore, enlarging their market potential. The development of new recycling technologies is diversified and can be classified into mechanical, chemical and energetic recycling. In mechanical recycling, successful technologies are achieved through the improvement of existing processes using additives, blends with other plastics and alternative processing routes in order to maintain the original properties of the virgin resin and even allowing them to return to the same application as originally intended. Chemical recycling processes to obtain intermediary products for new polymers become feasible due to the cost reduction of the raw materials involved. Lastly, despite the under use of the gross energy potential of the raw materials employed, energetic recycling plants are gaining a proportion of residues whose technological solutions for separation and/or reprocessing are deficient, but which, on the other hand, are voluminous, consequently solving the problem of both residue accumulation in densely populated regions and their respective insufficient energy supplies. In chapter one, the authors proposed to present an overview of the current state of this whole plastic recycling sector including their recent advances, and highlighting new markets and recent trends on recycling technologies around the world. However, mechanical recycling has been emphasized owing to the experimental and published work of Manrich’s workgroup at the 3R Residues

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Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling. Recently, fuel cell vehicles (FCV) are being developed to reduce the environmental impacts related to the conventional internal combustion engine vehicles. Although on the short term the newly proposed technology might serve the intended purpose. On the long term, there may be bottlenecks in the supply of specific metals required for the technology and new emissions may replace the old ones. Fuel cell technology requires the use of platinum, which is cited as a possible bottleneck for a more widespread use of the new technologies. Moreover, an increase in platinum demand ultimately implies an increased production of the co-produced metals Cu and Ni. Consequently an increased supply may well have environmental consequences on Ni and Cu recycling system. Chapter two is aimed at investigating the potential long-term impact of the increase use of platinum in fuel cell technology and other applications in terms of resource depletion and evaluating the long-term consequences of the increased demand of platinum on the cycles of other co-produced metals especially Ni and Cu. The analysis is carried out using a dynamic substance flow-stock model for platinum, nickel and copper. The model consists of a set of differential equation describing the change of the magnitude of the substance stock in the system compartments (production, use and waste management of platinum applications, primary production of platinum in South Africa, Russia, USA, Canada and others and secondary production of platinum) over time and several model relations. The model is implemented in Matlab/SIMULINK environment. The main driving force in the model is the global demand for platinum. The global demand for platinum is estimated based on the demand for its applications (fuel cell, catalytic converters, and the other applications) and platinum required for each application. In turn, the demand for platinum applications are modeled based on socio-economic variables such GDP, per capita GDP, population size, material price and the cost of these applications. Platinum required for each application is modeled as a function of cumulated production using the learning curve. In addition, several other factors are important in determining the main outcome such as the applications life span, the applications collection rates and the efficiency of the production processes (primary and secondary). The main model outcomes are the amount of primary platinum required for FCVs and other applications and the consequences on platinum current reserve, platinum identified resources and the co-produced metals recycling and primary production from other ores. The model shows that the demand for primary platinum will increase dramatically with the introduction of FCVs despite the possibility of the decrease of platinum loading of FC. This is mainly due to the increased demand for vehicles. Without changes in management, the current platinum reserve would be exhausted in three decades and the identified resources in roughly 60 years. The model also shows that the demand for the co-produced materials is increasing over time. The supply of these metals from Pt ores is, combined with only a part of their current secondary production, sufficient to meet the rising demand. Consequently the primary production of these metals from other ores than those of Pt ores will not be needed. Recycling of these metals is expected to decrease. Forest ecosystems are valuable both as species’ habitat and as one of the important lifesupport systems for the biosphere. The most severe effects of metals on forest ecosystems are from local pollution in the Subarctic regions, and the Kola Peninsula (66-70°N and 28°30'-

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41°30'E) in Russia is one of the most seriously polluted regions: since it is close to nickelcopper smelters, the deposition of metal pollutants has severely damaged the soil and ground vegetation, resulting in an industrial desert. The methods used for restoring an industrial wasteland should have regional character; i.e. features of the ecosystem and specificity of the nutritional regime. Global production of sewage sludge is estimated at ∼30 million tons/yr, and 70% of this amount is disposed of; however, it is recognized that compost produced from sewage sludge is effective in soil conditioning. Podzol is the most common soil type on the Kola Peninsula, and this type of soil is generally nutrient-poor. Plant growth is severely limited by nutrient availability in the Arctic (or Subarctic) ecosystem. Nutrients in pools of soil organic matter show slow turnover rates, so nutrients become available to plants at a low rate. Land remediation using compost seems to be effective in such podzol forest land damaged by the metallurgical industry. Using a soil-like substratum consisting of compost produced from sewage sludge, a rehabilitation test was conducted in the above-mentioned metal-polluted land (67º51’N and 34º48’E) over an area of 4 ha for the purpose of contemplating the feasibility of combining the application of unused sewage sludge with the recovery of damaged forest land. In chapter three, the following items were studied: (i) chemistry of the original sewage sludge; (ii) its transformation during composting; (iii) the effect of liming on compost properties; and (iv) abiogenic and biogenic transformation of soil-like substrata in the test field for assessing whether the effect of current pollutants on local vegetation is constrained. Based on field observation during 2003-2005, the obtained data showed the redistribution of organic matter and heavy metals. This suggests that the content of heavy metals in old artificial substrata may be less than that in fresh artificial substrata. In conclusion, the test field of 4 ha is recovering from degradation of the podzol forest land. Almost all the metallurgical processes are associated with the generation of wastes/residues which may be hazardous or non-hazardous in nature depending upon the criteria specified by institutions like US EPA etc. The wastes containing heavy and toxic metals such as arsenic, cadmium, chromium, nickel, lead, copper, mercury, zinc etc. are present beyond permissible limits deemed to be disposed of. Due to the implementation of stricter environmental laws and economic reasons all the metallurgical industries are now forced to go for eco-friendly technologies to produce metal and other related products world over. However, generation of wastes is the integral part of metallurgical industries which can not be ruled out, therefore if the wastes/residues are hazardous in nature they generally have to be treated or disposed off in safe and designated dumping sites. If these wastes/residues are non-hazardous in nature then they may be suitably used as secondary raw material for the recovery of metals which are in growing demand all over the world. Zinc is in growing demand all over the world. In India a major amount of zinc is imported and therefore processing of zinc secondaries will supplement in satisfying the gap between demand and supply to some extent. Similarly processing of lead secondaries is important because of their relative high metal content, besides low energy and cost involved in recovering the metal. Chapter four highlights the production capacity, type and quantity of solid wastes generated, their chemical composition and treatment/disposal options for the Indian lead and zinc industries. Zinc tailing, slag, leach residue, jarosite residue, β-cake, etc. from zinc industries and BF slag, flue dust, ISF slag etc. from lead industries are the major solid waste generated from various process and needs attention. Although all the metal producing industries in organised sector are now taking care of the environment and waste management related

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problems, but pollution from unorganized lead units are the major cause of concern. Permissible limits of toxic constituents in zinc based secondaries and threshold zinc concentration for both indigenous and imported raw materials were worked out at National Metallurgical Laboratory (NML). An overview of the current practices and recent trends in the secondary processing of zinc and lead and the attempts made to recycle/recover metal values and production of value added products, are discussed in the text. Various processes, particularly hydrometallurgical ones, already developed or in the developmental stages, are discussed. Attempts made by various laboratories and industries towards the development of eco-friendly processes for the recovery of zinc and lead from secondary raw material are also described. A review of the production of activated carbons from wastes, such as agricultural and used tires, by using atmospheric pyrolysis, is presented in chapter five. Pyrolysis of waste is a CO2-neutral process and can transform biomass to energy and materials. It is a possible way for chemical recycling of the organic matter. This study evaluates pyrolysis of olive kernels, olive wood, and cotton ginning waste and used tires, by studying the effect of temperature on the pyrolysis product yields and investigates production of activated carbon from pyrolytic char. A comparison in characteristics and uses of activated carbons from agricultural residues and tires with commercial carbons have been made. Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. Waste incineration thereby links the systems of waste management and energy. Chapter six addresses the importance of taking this into consideration when e.g. making investment decisions or designing policy instruments. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed, together with trading in waste and electricity and how this impacts waste incineration in Sweden. Conflicts between the internal market in the European Union and waste management goals are shown. When making investment decisions, various models are often used as decision support tools. Some models for assessing waste incineration/management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration. The waste employed in this work presented in chapter seven comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both fly ash samples coming from these two equipments have been individually employed. Ash from waste incineration plant is classified as hazardous and cannot be utilized or even landfilled without prior treatment. This chapter reports the results of an extensive investigation on stabilization/solidification of the above ash samples by addition of hydraulic binders in a granulation equipment. A rotary plate granulator was used with binders based on cement, lime and coal fly ash. Granulation was carried out with several mixes in which the ash content was up to 70%. In some cases, the granules obtained in this way are suited for matter recovery by reusing the waste for the manufacture of building materials. To achieve this in most cases, two-step granulation is required with pure binder being used in the second one. In this way the granules from the first step can be encapsulated within an outer shell able to improve the technological and leaching properties. The possibility to get matter recovery from incinerator ash is a crucial issue for making the

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granulation process environmentally and economically sound. In fact, the most direct application of granules is in the field of artificial aggregates for road construction and concrete manufacture. The granules obtained from the treatment of fly ash samples have been tested to assess their physico-mechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive (crushing) strength and leaching behavior. Moreover, concrete mixes have been prepared with some of the artificial aggregates made by granulation. Once hardened, these mixes have been successfully tested from the technological point of view, proving to be suitable for the manufacture of classified concrete blocks. Chapter eight investigated the properties of municipal solid waste incinerator (MSWI) ashes and the effects of their addition on the municipal solid waste (MSW) anaerobic digestion as co-disposed or co-digested with MSW in landfill or digester. Five anaerobic bioreactors with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers were arranged each with 6.5 liter of MSW and anaerobic seeded sludge mixture covered by 2.5 liter of MSW and anaerobic seeded sludge mixture blended with the designed ashes added ratios as well as the control bioreactors without ashes addition. The synthetic MSW used in this experiment was typical of organic fraction of MSW and was comprised of newspaper, food waste, office paper and hay etc. MSWI ashes were obtained from a mass burning incinerator in central Taiwan. Also, the seeded anaerobic sludge was taken from a municipal wastewater treatment in central Taiwan. As the experiment was proceeded with, the leachate of 100 mL was recirculated per day and another more 100 mL one was collected and filtered for parameters analysis such as pH, conductivity, alkalinity and chemical oxygen demand (COD) etc. In addition, the gas production rate was recorded every day to measure the bacterial activity in the MSW biodegradation. From the results, it showed that 10 and 20 g l-1 fly ash added (g ashes addition per liter MSW ratios) bioreactors and 100 g l-1 bottom ash added bioreactors were found to enhance the gas production rate and the soluble concentration of alkali metals such as Ca, Mg, K, and Na as compared to the control one. The six soluble heavy metals of Cd, Cr, Cu, Pb, Ni and Zn in leachate were also found to be under inhibitory concentration for anaerobic digestion. Other trace metals such as Co and Mo etc were assumed to serve as the stimulatory micronutrients rather than to exert inhibitory effects on the microorganisms in the MSW anaerobic digestion.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 1-60 © 2006 Nova Science Publishers, Inc.

Chapter 1

AN OVERVIEW OF RECENT ADVANCES AND TRENDS IN PLASTIC RECYLING Sati Manrich∗ Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil

Amélia S. F. Santos Instituto de Pesquisas Tecnológicas do Estado de São Paulo, São Paulo, Brazil

ABSTRACT Since the discovery of plastics several decades ago, the widespread consumption of plastic products and their subsequent inappropriate disposal and accumulation have recently generated new societal concerns of waste management due to their inherent slow degradability, high volume increase and low recycling rates, which are negative on the basis of self-sustainability. Regulations imposing waste reduction, reuse and recycling indices and responsibilities, as well as effective collecting system and the development of new, environmentally clean recycling technologies are some of the efforts to achieve the self-sustainability goals. The efficiency of the collection and sorting systems impacts directly on the amount of recycled plastics and on their cleanness and quality, therefore, enlarging their market potential. The development of new recycling technologies is diversified and can be classified into mechanical, chemical and energetic recycling. In mechanical recycling, successful technologies are achieved through the improvement of existing processes using additives, blends with other plastics and alternative processing routes in order to maintain the original properties of the virgin resin and even allowing them to return to the same application as originally intended. Chemical recycling processes to obtain intermediary products for new polymers become feasible due to the cost reduction of the raw materials involved. Lastly, despite the under use of the gross energy potential of the raw materials employed, energetic recycling plants are gaining a proportion of residues whose technological solutions for separation and/or reprocessing ∗

Corresponding author: [email protected], phone: 55-16-3351-8503.

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Sati Manrich and Amélia S. F. Santos are deficient, but which, on the other hand, are voluminous, consequently solving the problem of both residue accumulation in densely populated regions and their respective insufficient energy supplies. In this chapter, the authors proposed to present an overview of the current state of this whole plastic recycling sector including their recent advances, and highlighting new markets and recent trends on recycling technologies around the world. However, mechanical recycling has been emphasized owing to the experimental and published work of Manrich’s workgroup at the 3R Residues Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling.

INTRODUCTION For sustainable development and the limitation of environmental impacts to become a realistic goal, reduction of the currently growing consumption of non-renewable natural resources, reuse of products following consumption and appropriate recycling of discarded residues are of paramount importance. The effective practical application of the “3R” concept is especially important for the burning of carbon-releasing energy sources to be minimized. Some studies have indicated that, even if all emissions of CO2 and other greenhouse gases were stopped immediately, the climate changes that have already occurred on the planet would remain for some decades. Since from the stand-point of thermodynamics and engineering practice, it is impossible to end such emissions altogether, efforts have to be made to reduce the risks to the environment, whenever the opportunity arises [1-3]. The reuse and various types of recycling of waste residues can lead to reductions in the use of non-renewable material and energy resources, with the energy savings generally ranked as follows: reuse > material recovery > energy recovery (energy from waste). Conversely, burying the residues in landfills, entailing as it does the total loss of material and energy, makes no such contribution [2, 4]. In the case of plastics, whose main current source of raw material is the petroleum, all recycling methods are technically viable and are briefly described next [5,6]. Mechanical recycling consists of the reprocessing of plastic residues into new products, different from or similar to the original products. The waste plastic used may come from the manufacturing process or from post-consumer products. This is the simplest way of recycling plastic waste, demanding the lowest initial investments. Chemical or feedstock recycling consists of using heat or chemical treatment to break down plastic residues into their basic chemical components, the monomers or other products, which can then be recombined into polymers or used for other applications. Typical examples of tertiary recycling processes are hydrolysis and pyrolysis. Unfortunately, this kind of recycling demands huge investments and is therefore viable only for large-scale operations where the volumes processed are comparable to those in the petrochemical industry (thousands of tons annually). Quaternary or energy recycling is the recovery of the energy bound in the plastic, by combustion, thus economizing on fossil fuels. However, the operation of such processes must guarantee that the emission of volatiles is controlled, to prevent the environment being contaminated by other paths [7, 8]. Recently, this type of process has been excluded from the normal concept of recycling and mentioned only as a form of energy recovery. In fact, this

An Overview of Recent Advances and Trends in Plastic Recyling

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line of recycling is often regarded as a wasteful underutilization of the gross energy stored in the plastic. Even though all the methods of material and energy recovery from plastic waste are technically feasible, in practice they encounter economic, legislative, market and other barriers. Published contributions in regulations, management and recycling of plastic waste using all forms of media are numerous around the world. Frequently, in books of edited contributions dedicated to plastic waste, each chapter deals separately with one of the topics covered. In this chapter, we present an overview of the current state of the whole plastics recycling sector, if somewhat sketchily in some areas, including a brief review of the recent research and development in the fields of mechanical, chemical / thermochemical and energy recycling of plastic waste. However, there is an emphasis on mechanical recycling, owing to the experimental and published work of Manrich’s workgroup at the 3R Residues Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling.

WASTE MANAGEMENT OF PLASTICS RESIDUES Since the emergence of plastics in the 1940s, which was impelled by their notable costbenefit advantages over the traditional materials they replaced, the concepts of security, comfort and hygiene have been improved. In addition, their intrinsic characteristics of lightness, low processing temperatures, durability, low thermal and electric conductivity, transparency and flexibility, among others, had an immediate and growing impact on the correlated manufacturing sectors, reducing consumption of both energy and natural resources. Furthermore, the plastics industry was enormously successful in developing novel materials such as plastic wood, synthetic leather and paper. On the other hand, the mounting volume of plastic residues, coupled with their extremely low biodegradability, generated a serious problem regarding the amount of space they took up. In the developed countries, the large urban centers have real difficulties in finding space for all the refuse, needing in some cases to transport solid waste over long distances to its final destination [9]. This problem, along with those arising from poor disposal methods and the associated environmental impact, the high added value of waste, the need to promote sustainable development of the production chain and to educate people to be more aware of the environment, has stimulated much research and practical activity in the fields of the recycling, degradability, reuse and reduced generation of plastic waste. In view of the fact that plastic is said to compose between 5% and 10 % by weight of municipal solid waste (MSW) [10-12] and yet is the material of which the smallest fraction is recycled [13, 14], there is an ongoing discussion among government, society and the manufacturing sector on the apportionment of responsibility for the management of plastic residues in MSW [15]. The difficulty in recycling plastics arises largely from the big fraction of plastic products considered unsuitable for recycling from the outset and from the high operational cost of plastic´s collection systems. Several mechanisms have been employed to increase the viability of the reversed logistics of returning the end-product packing material to the recycler: taxation of the

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manufacturing sector about government regulations [16] the establishment of taxes on nonrecyclable packaging [17] the mandatory use of recycled materials in some sectors [9] incentives on the use of articles made entirely of such materials, with the removal of all licensing requirements on those who wish to produce them [18] the opening of new markets for recycled plastic, implementation of policies of exchanging post-used packages etc. for toys, spendable vouchers, or sports material in needy communities [19, 20] and lastly programs to inform, raise public awareness and provide opportunities for consumers to play their part [21]. In parallel, initiatives used to improve the recyclability of packaging by manufacturing plastics parts with fewer different resins and with easier separation of components that contain distinct resins, and reduce the use of multilayered material [13] adhesives, additives and labels on packs also play an important role [9]. Thus, in various parts of the world regulations have been adopted in order to achieve short and medium-term recycling targets [13]. In the European Community (EC), which became the European Union (EU) in 1992, the goals for rates of recovery and recycling in the packaging sector were set by the Directive 94/62/EC [22] to member countries, establishing June 2001 as the deadline by which these goals had to be reached: recycling of at least 25% and at most 40% by weight of all waste packaging and recovery of at least 50% and at most 65%. In addition, for each specific type of material, the fraction recycled should be at least 15%. The available data confirm that these projected rates have been achieved in paper recycling in the EU [23]. Considering the plastic packaging sector, in Germany, the country that recycles the highest fraction of its waste in Europe, these targets have also been accomplished, or at least approximated, except in the case of composites. New EU targets for individual types of plastic waste have already been outlined for 2006, in which at least 20% of each type should be recycled [23]. These targets are currently being revised by the EU, but national governments, such as the UK, are also reconsidering their own packaging recycling and recovery targets for 2008 [21]. The particular concern over post-consumer plastic from the packaging sector can be explained by its short useful life, which reflects in its fraction 75% of all plastic waste [24]. In the EU, the recovery of plastic packaging residues was boosted mainly by improvements in mechanical recycling that resulted from better solid residue management practice [25]. The system of selective waste collection used in Germany, organized by Dual System Deutschland (DSD), is a worldwide reference [26]. In the EU countries in the decade from 1993 to 2003, generally speaking, the mechanically recycled fraction of all discarded plastic rose from 5.6% to 14.9%. Over the same period, largely because of the contribution made by energy recycling indexes, the fraction of plastic in landfill fell from 75.7% to 61% [14, 25, 27]. In Japan, the equivalent fraction for solid residues in sanitary tips is around 40% and much of this waste goes for energy recovery. The use of energy recycling in those countries is justified by the reduced combustion of fuels to produce energy, by the release of oil for the manufacture of virgin plastics and by the provision of an alternative source of energy that reduces the problem of energy shortage. Similarly, in 2000, about 11% of all plastic produced in the USA was recycled. This represents a great advance, since a mere 1% of plastic residues were recycled in 1987 [9]. Nevertheless, this advance in recycling indexes has been achieved by formal recycling

An Overview of Recent Advances and Trends in Plastic Recyling

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regulations [28]. Relating to Poly(ethylene terephthalate) (PET) recycling indexes, the USA is currently going through a period of stagnation in the recycling of this resin, according to the annual reports published by the American Plastics Council (APC), in spite of the very high recycling levels of PET achieved in 1995. At most, the amount of recycled PET is increasing in proportion to the growth in production of the resin [17, 29]. In 2001, the fraction recycled did not actually fall, but only because the slack in the home demand was absorbed by the export market [17, 30]. In 2004, the fraction of recycled PET was of the order of 21.6%, according to the National Association for PET Container Resources (NAPCOR) [31]. Turning to Brazil, in a national survey carried out by Plastivida, the plastics division of the Association of the Brazilian Chemical Industry (ABIQUIM), the proportion of plastic residues transformed by mechanical recycling is around 16.5%, higher than that in Europe [32]. Furthermore, Brazil is the third biggest market in the world for bottle-grade PET [18, 32] and the amount of this resin sent for recycling is of the order of 35% [20, 34, 35]. Given the precarious state of waste collection system in Brazil, such high rates of recycling are achieved only with the spontaneous involvement of low-income families whose earnings come largely from collecting plastic residues [20, 35]. This segment of the population currently represents about 500,000 informal workers [32]. Finally, another type of residue demands our attention: the great volume of rubber tires discarded annually in Brazil and accumulated annually around the world [36, 37]. Since the beginning of the nineties, many Federal and State Government ministries have been developing their own legal responsibility for this residue. In Brazil, resolution 258, passed by CONAMA (National Council for the Environment), obliges tire manufacturers and rebuilders (of retreads, remolds) to provide an environmentally correct destination for an amount of used tires proportional to their volume of production since 2002 and 2004, respectively [38].

FIRST STEPS OF PLASTIC MATERIAL RECOVERY PROCESS: SORTING AND CLEANING Sorting One of the stages of plastic recycling that most threaten its feasibility as a productive operation is the sorting of plastic material from mixed waste and, especially, separation of the different types of plastic, which is hindered by the fact that quite different plastics may be used for the same end. In other words, a given product can be fabricated with very similar characteristics from distinct plastics and these act, in mixed residues, as impurities of each other after separation. This reduces the viability of the process and, in serious cases, can cause a whole production line to be shut down [39, 40]. Related problems that must also be taken into account are those of multicomponent items, good examples being car parts and plastic electric and electronic devices with embedded metal inserts, and multilayered products such as laminated, co-extruded or metalized flexible packaging [39-41]. The ideal practical solution to this problem would be to make suitable alterations in the plastic residues at source; that is, to redesign the original plastic product. At the design stage, then, priority should be given to reducing the number and variety of components in one

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product and the variety of materials employed as consumer goods with identical functions. Such ideas are exactly the opposite of current design trends, particularly in the packaging and disposable goods sectors. In most cases, the existence of multicomponent and multilayer residues is justified primarily on technical grounds, while the reasons for fabricating essentially the same product from diverse materials are based on economics and marketing [41]. It is thus hard to imagine the above-mentioned reversal in product design trends becoming a manufacturing priority on the grounds of purely environmental gains. Nevertheless, on the positive side, all over the world we see a lot of effort being put into the research and development of appropriate technology that will minimize the problems caused by mixed plastic waste and varying materials. These studies concentrate on two fronts: the efficient separation of different plastics and other components, and optimization of the composition of compatible blends, or plastic composites of different materials, that combine, profitably, the distinct properties of the component polymers [39-46]. The first of these research areas will be discussed here and blends and composites in later sections. The techniques used to separate mixed plastic residues can be classified in several ways, but here they will be grouped as manual or automatic and each will be approached in a specific way.

Manual Separation The efficiency and productivity of this method depend entirely on the experience of the workers responsible for identifying and sorting the plastic residues. This is the method used in the vast majority of micro and mini-enterprises in developing countries, where manual labor is cheap, and in Materials Recovery Facilities (MRFs) worldwide, although it is still used even in some large organizations that recycle electro-electronic residues in developed countries [39, 42]. When training technical personnel in the manual separation of plastics, basic notions of how to distinguish between these materials have to be introduced. A systematic procedure for the identification of components of municipal plastic waste, especially the most prevalent plastics, which was proposed in an earlier publication of the Manrich’s workgroup, has until now helped the Brazilian public to achieve this aim [39]. This method consists of three steps: in the first, the identification is made directly by codes; in the second, the identified product is correlated with the most likely material, and in the third, certain properties specific to each material are determined. The three steps are briefly described next. −

−

Step 1: Locate the identification code and note the number or abbreviation found in the recyclable plastic symbol: 1 = PET, 2 = HDPE, 3 = PVC, 4 = LDPE/LLDPE, 5 = PP, 6 = PS and 7 = others, where HDPE, LDPE and LLDPE are high density, lowdensity and linear low density polyethylene, respectively, PVC is poly(vinyl chloride), PP is polypropylene, and PS is polystyrene. However, the residue from a product, part or component does not always display a code, which may be molded in relief or printed on the surface. If the code is missing or identified as 7, the procedure has to move on to the following steps. Step 2: Consult a table of data, such as Table 1, which helps the user to identify the most likely material in a given product. It is found that, contrary to what would be

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7

environmentally correct, the number of most probable materials rises through the years, albeit rather slowly. Hence, from time to time, these tables need revising. Table 1. Polymers used most frequently in fabrication of packaging material. Type of packaging

Bottles

Pots, containers and trays

Lids

Plastic bags

Typical use Carbonated soft drinks Cleaning materials and toiletries Cooking oil Mineral water Vinegar Yoghurt drinks Margarine Yoghurt Sweets and chocolates Disposable plastic cups Prepacked fruit & vegetables Soft drinks Cleaning materials and toiletries Cooking oil Vinegar Yoghurt Margarine Mineral water Sweets and chocolates Supermarket bags Fruit and vegetable bags

Films† Biscuits and snacks bags

Most probable material* PET HDPE, PP, PVC PET, PVC PET, PP, PVC PP, PVC HDPE, HIPS, PP HIPS, PP HDPE, HIPS, PP PET, PP, PS, PVC HIPS, PP PS, PVC PP HDPE, PP HDPE, PP LDPE HIPS, PP HIPS, PP LDPE, HDPE, PP HDPE, HIPS, PP, PS HDPE, PP LDPE, LDPE/LLDPE, HDPE, PP LDPE, LDPE/LLDPE, PP

*

While these materials are the most likely ones, the packaging can be made from others. † Film is a term used for plastic sheets 254 µm or less thick, normally used in shopping bags.

−

Step 3: Given the list of most likely plastics, determine some specific distinguishing properties that are simple to compare; these are indicated below, for the case of postconsumer plastic packaging. Here we will omit the techniques of differential scanning calorimetry and infrared spectroscopy. Depending on the plastics in question, identification may be achieved by testing only one of these properties, or a sequence of tests may be required. This sequence varies from case to case and an example will be given later, for the case of plastic bottles. − Transparency: transparent ⇒ PET, PP, PVC, PS; translucent or opaque ⇒ HDPE, PP, high-impact polystyrene (HIPS), LDPE/LLDPE, PET. − Whitening: exhibit whitening when folded ⇒ PP, HIPS, PS, PVC. − Hinge: PP is the only plastic that withstands the repeated force used to open and close the pack with a one-part device, the hinge.

8

Sati Manrich and Amélia S. F. Santos − − − −

−

Density: the polyolefins, (HDPE, LDPE, LLDPE, PP) and expanded polystyrene (EPS) float on water, being less dense (ρ < 1.0 g.cm-3). Combustion: the flames and smoke given off by burning plastic are characteristic of each type. Table 2 describes these features of several plastics. Solubility: ability to dissolve in various liquids or solvents is specific to each plastic. Table 3 shows some examples. Halogen or Beilstein test: if a copper wire is heated to redness, rested on the plastic and then returned to the flame, and the flame turns green, the residue is a halogenated plastic, such as PVC, which contains chlorine. Hardness and malleability: it is very hard to distinguish polyolefins from each other by means of simple tests alone. Experienced technicians differentiate the polyethylenes, LDPE and HDPE, from other plastics, including PP, as they are readily scratched with the fingernail, whereas the rest are too hard. Since LDPE is more malleable than HDPE and PP, it can be distinguished by bending or pressing the article.

Table 2. Behavior on combustion of the main polymers found in MSW. Material

pH of smoke Odor of smoke

HDPE, LDPE, LLDPE PS, EPS, HIPS, ABS PP

Neutral

PVC

Acid

PMMA

Neutral

NYLON

Basic

PET PC

Neutral Neutral

PU

Neutral

Cellophane (regenerated cellulose)

Basic

Neutral Neutral

Burnt candle

Color of flame

Yellow with blue base Styrene smell / Yellow with blue with much soot base Burnt candle Yellow with blue base Acrid Yellow with green base Methyl Yellow with blue methacrylate base (acrylic) Burnt hair Blue with yellow tips Sweetish Yellow Phenolic Yellow (carbolic) Acrid, pungent, Yellow with blue sour base Burnt paper or Greenish-yellow plant material

Ignition/ selfextinguishing

Ignites Ignites Ignites Self-extinguishes Ignites

Ignites Ignites Ignites Ignites Ignites

An Overview of Recent Advances and Trends in Plastic Recyling Table 3. Solubility of polymers in various solvents. Polymer Soluble in HDPE Decalin*, tetralin*, xylene† LDPE Heptane*, xylene*, decalin*, tetralin LLDPE Xylene†, decalin*, tetralin* PP Xylene†, decalin*, tetralin* PET o-chlorophenol*, nitrobenzene*

EPS, PS ABS, HIPS PVC NYLON

PC PMMA PTFE * †

Chloroform, xylene, tetrahydrofuran (THF), ethyl ether Chloroform, xylene, THF, methylene chloride Cyclohexanone, MEK, DMF, THF Formic acid, phenol, trifluoroethanol, concentrated sulfuric acid Chloroform, cyclohexanone, DMF, cresol, methylene chloride Acetone, toluene, chloroform, MEK, THF Insoluble (soluble only in fluorinated kerosene at 300°C)

Insoluble in Ethyl alcohol, chloroform, benzene, acetone Ethyl alcohol, chloroform, benzene or petroleum ether, acetone Ethyl alcohol, chloroform, benzene, acetone Ethyl alcohol, chloroform, benzene, acetone Xylene, ethyl alcohol, chloroform, benzene, acetone, cyclohexanone, methyl ethyl ketone (MEK), dimethyl formamide (DMF), THF Alcohols

Alcohols, benzene Chloroform, alcohols, xylene Alcohols, chloroform, xylene, acetone

Alcohols, benzene, acetone

Soluble at temperatures above 50oC. Soluble at temperatures above 100 oC.

Table 4. Practical test sequence suggested for plastic identification from a mixture of waste plastic bottles. Property

Transparent

Translucent

Probable material

PET, PP, PVC

HDPE, HIPS, PP

Property

Opaque HDPE, HIPS, LDPE/LLDPE, PP, PET Density < 1 Density > 1

Whiten Do not Whiten Do not when folded whiten when folded whiten Probable material PP, PVC PET, PVC HIPS, PP HDPE HDPE,LDPE HIPS, PET / LLDPE, PP Density Hardness Comb. Halogen test Halogen test Density Further tests Comb. Comb. Malleability Solubility Density Comb. needed to Solubility Solubility Comb. complete or Solubility confirm identification

9

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Sati Manrich and Amélia S. F. Santos

The test sequence suggested for the specific case of bottles is shown in Table 4. It must be said that manual separation of a mixture of PET and PVC bottles etc is quite easy, since carbonated soft drink bottles are all of PET and the rest can be differentiated by inspecting the base. If the bottle was injection molded as a preformed, then blow-molded with an injectionpoint at the middle of the base, it is made of PET; if it was extrusion parison blow-molded, with a weld-line across the base, it is PVC.

Automatic Separation Automatic separation, like manual, is based on differentiating a given plastic in the waste from the rest by means of its physical or chemical characteristics. The main properties exploited are density, chemical structure, solubility, surface character and electrostatic and thermomechanical properties. Density In plastics recycling, apart from the traditional and modern hydrocyclones that separate materials by density differences as little as 0.01 g.cm-3, there are simpler processes, with separating tanks containing aqueous solutions of various densities. The sketch in Figure 1 shows how this might be done in the case of typical mixed municipal plastic waste.

LLD/ LDPE PP

Floating waste

Sinking waste

HDPE LLD/ LDPE PP

HDPE Water + 40-45 wt% ethanol

PP LLD/ LDPE Water + 50-55 wt% ethanol

PS PET PVC PS

100% Water

PVC PET Water + 20-27 wt% NaCl

PP LLD/LDPE HDPE PS pPVC uPVC PET

ρ (g/cm3) 0.89-0.91 0.91-0.94 0.94-0.96 1.04-1.10 1.16-1.35 1.35-1.45 1.33-1.39

Figure 1. Separating tanks with water solutions for sorting municipal plastic waste.

Tsunekawa et al [42] have developed a process using density differences, based on experiments in the laboratory and in a pilot plant designed to separate plastics, recovered from scrapped copying machines, by a jigging method, which has culminated in a commercial plant, built recently to recycle office equipment, domestic appliances and automobile shredder residue. Jiggers have been used in the technology of separation for a long time and are widespread mining sector. In this technique, water covering the material is pulsed at given amplitudes and

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frequencies, and the jolting of the solid particles results in their forming stratified layers arranged in order of density. In this plant, the TACUB Jig [42] was used and adapted to separate a ternary mixture of milled PS, acrylonitrile butadiene styrene (ABS) and PET, whose respective densities are 1.06, 1.18 and 1.71 g.cm-3. Water density was raised by adding zinc chloride. The pilot studies showed that, apart from the amplitude and frequency of the pulses in the water, other factors affected separation efficiency, including: height of the liquid (bed thickness), float level, water flow-rate and waveform. When performance was optimized by varying these conditions and analyzing the results, the plant separated 99.8% of the PS, 99.3% ABS and 98.6% PET for the ternary mixture.

Chemical Structure Plastics can be differentiated and separated on the basis of atoms or bonds specific to their chemical structure, with the aid of devices based on infrared (IR) spectroscopy. Plastic residues, whole or ground into flakes, can be placed on a conveyor belt and scanned continuously by such a device, whose IR radiation source is adjusted to the absorption wavelengths of the plastic in question. Any change in the absorption spectrum discloses the presence of an impurity at a specific point on the belt at that moment, thus defining the exact position and time, moments later, where a jet of compressed air should be activated. The foreign object is blown off the belt, to land on another, below the first, moving at right-angles to it and so effecting the separation [44]. By exchanging the IR source for one radiating in the ultraviolet-visible range (UV-VIS), the traditional technique used to separate glass by color can be employed. The advantage of equipment of this type is that plastic residues previously ground into flakes can be automatically separated, using different sources of radiation. Solubility The solubility profile of each plastic, already mentioned in connection with manual separation, is also the basis of automatic separation by selective dissolution. This can be used in two ways: either the plastic to be separated is extracted in a solvent that does not dissolve the others, or the residue is extracted batchwise with a common solvent that dissolves each plastic at a different temperature [45, 46]. Van Ness and Noster [46] presented the outline of a selective extraction process and the results of trials of the proposed method, performed by Linch Naumam with a mixture of known composition, containing virgin resins (LDPE, HDPE, PP, PS, PVC and PET), and a real mixture of post-consumer plastic residues. The efficiency of separation was found to be better than 99% in the case of the virgin resins, when tetrahydrofuran (THF) and xylene were used for selective dissolution at more than one temperature. However, it was not possible to separate PS from PVC at room temperature, or HDPE from PP at 160 °C, with THF. In general, for the plastic mixtures discussed here, separation by density (see above) is more practical, as it is cheaper and environmentally friendly; however, it will not separate PVC from PET. When these are present, selective dissolution could be alternatively employed as a complementary final step, using xylene at 138 °C. In addition, solvent extraction is suitable for multicomponent or multilayer residues [41, 47].

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Sati Manrich and Amélia S. F. Santos

Surface Properties Most plastics exhibit low surface energy, making them hydrophobic. Despite this, the surface of plastics can be wetted by treating them with surfactant solutions, making them hydrophilic. The surfactants normally used for surface treatments consist of molecules with an affinity for organic polymers, but which also have hydrophilic groups. These surface modifiers are not equally efficient with all plastics, so that a given surfactant may be most effective for a specific plastic. These differences are exploited in the separation of residues by the method of froth flotation [48, 49]. The method is basically to put the treated plastic residues in a tank of water containing a frother and then introduce air-bubbles, which tend to stick to the hydrophobic particles, for which the surfactant was less effective. The clusters of bubbles and particles usually rise to the surface of the bath, in contrast to the hydrophilic particles, allowing the different materials to be separated. Research on selective froth flotation focuses mainly on binary mixtures of PET and PVC [48, 49]. Drelich et al [48] applied the surface treatment in strongly alkaline solutions of caustic soda and used C9-11 ethoxylated alcohols as frothers in the flotation tank. The preliminary treatment made the PET hydrophilic, while hardly affecting the hydrophobicity of the PVC, and this was confirmed by measuring the advancing and receding water contact angles on each surface. The efficiency of separation attained was 95-100% in a variety of PET/PVC mixtures and flotation conditions. In the work of Marques and Tenório [49], the surfactant used was calcium lignin sulfonate and the frother methyl isobutyl carbinol. Some of the experimental conditions were again varied, as were the sizes of PVC and PET particles. In the best conditions, 98.9% of the PVC and 99.3% of the PET were separated, at purities of 99.3% and 98.9% respectively. Electrostatic Properties The separation of several types of plastic packaging on the basis of differential triboelectrification was investigated by Hearn and Ballard [50]. The triboelectric effect is induced by rubbing two materials together so that, on separation, one retains a negative electrostatic charge and the other, a positive one. If two different plastics are rubbed against a third material chosen as a suitable reference, the charge generated on the latter should be positive with one plastic and negative with the other. In the cited work, polyvinylidene fluoride (PVDF) and poly(butylene terephathalate) (PBT) were tested as triboelectric probes for the separation of mixed packaging residues of HDPE, PET, PP, PS and PVC. From the results, a separation line was proposed for domestic waste in which the PVDF and PBT probes were mounted in sequence along a conveyor belt. At the first probe, PP would be separated from the rest as the only component to be charged negatively by PVDF. At the second point, PET and PS would receive a negative charge from PBT and thus be separated from the remaining mixture of HDPE and PVC, which would be positively charged. No method was suggested to separate PET from PS, but it was proposed that a visible light-based device could recognize and separate transparent objects like PVC from opaque ones such as HDPE. Once again it is worth remembering that, to separate this kind of mixture, it would be preferable to try other techniques that are simpler, cheaper, more practical and efficient.

An Overview of Recent Advances and Trends in Plastic Recyling

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Thermo-mechanical Properties The mechanism by which a material suffers mechanical fracture, brittle or ductile, depends mainly on the temperature and rate of strain. If a mixture of two plastics is ground under specific conditions that cause each material to break in a distinctive way, the resulting particles will have different shapes and sizes that might be separable later by sieving or by means of air cyclones or hydrocyclones. This way of separating binary mixtures of plastics can be applied when there is a temperature range where the two brittle-ductile transition temperatures are different from each other, in which the two plastics would break in different failure mode. In their study, Green et al concluded that the processing window of temperatures for selective impact grinding of a mixture of PET and PVC could be predicted from tensile stress tests and measurements of β-relaxation properties of each plastic [51]. Green et al [51] refer to two cases of processes, one in a patent and one used by a company, which produced particles of PVC smaller than PET after mixtures were crushed or subjected to impact grinding. In the case of cryogenic grinding, it was possible to recover PVC, 99% pure. A more recent approach to separating mixtures of plastics by their thermal transitions, which took into account the effect of dirt present in the residues, was proposed by Saito and Satoh [52]. In this study, the differing thermal adhesion behavior of different plastics was analyzed by employing two unsteady heat conduction apparatus. One consisting of a plate to heat, press and then to pull the adhered plastic pellets, so as to determine the adhesion temperature and the effects of varying some parameters, and the other counter-rotating twin rollers were used to improve the efficiency of adhesion. Tests were carried out on a mixture of pellets of PET, LDPE, PS, HDPE and PP. Generally, the thermal adhesion temperature of a polymeric substance is specific to each material and related to its glass transition or melting point. Saito and Satoh [52] showed that the size and shape distributions of the pellets affect adhesion, but within a characteristic temperature range for each material. Their proposed method succeeded well in separating a mixture of three plastics, PET, PS and PP. While these authors and collaborators showed that dirt caused only a slight rise in the adhesion temperatures, it remains true that a real mix of residues is very different from pellets, especially in terms of the shape and size of the particles. The separation of wasted plastic flakes needs to happen before extrusion into pellets, which would remains as a great challenge to be solved by this methodology.

Cleaning As previously mentioned, the collection of the residues from which used plastic is salvaged play an important role in raising the recycling indexes [31, 35]. On the other hand, that activity is also directly responsible for the extent of contamination of plastic residues, which in turn has a strong influence on the cleaning process and hence on the effluent discharged. It is clear that plastics, during their use and disposal, come into contact with other compounds, and their composition may be changed by contaminants permeating through and

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Sati Manrich and Amélia S. F. Santos

impregnating the material [53]. Thus, before recycling it is necessary to determine the extent of contamination, the contaminating chemicals and the intended use of the end-product, in order to adapt the cleaning technique as appropriate. Processes employing aqueous solutions are normally used to remove surface contaminants [54, 55]. However, these are not so effective in removing hydrophobic compounds or those that have migrated into the polymer matrix. These solutions generally contain caustic soda and surfactants, the proportions and flow-rates varying according to the type of material being recycled. Usually this is a continuous process in which the plastic, previously grinded into flakes, is vigorously shaken in the cleaning solution. The concentration of the alkali depends basically on the amount of glue and labels attached to the flakes [54]. The removal of adhesives is important, especially for polymers susceptible to degradation in acid conditions, because at reprocessing temperatures, adhesives decompose to acids compounds. Apart from sodium hydroxide, alkaline reagents commonly used include calcium hydroxide (lime), potassium hydroxide, sodium silicate, etc. The preferred alkaline fluid for this purpose is normally a mixed solution of 33% sodium hydroxide and 15% potassium hydroxide (caustic potash), although the susceptibility of a given polymer to degradation in alkaline conditions has to be taken into account when choosing these reagents [56]. The concentration of caustic soda used is usually adjusted to provide the desired alkalinity [54]. The concentrations of surfactants used are normally between 75 and 200 ppm. These agents are important in many real situations where the surfaces are contaminated with soil or microorganism. To choose a particular cleaning agent, it is necessary to consider the soil type, oil residues and unusual paints likely to be encountered. Other factors, such as the cleaning equipment, pH, liquid or solid state, work safety, environmental laws and costs of disposal should also affect the choice of the correct cleaning agents [55]. The cleaning step, in most cases, takes between 5 and 20 minutes at temperatures up to 88 °C. Short times do not suffice to remove adhesives, while periods exceeding 20 minutes give a low return, while the use of baths at high temperatures facilitates the removal of glue [55]. In view of the nature of the cleaning process and its relevance to the quality of the recycled product, it is vital that recycling activities that involve washing procedures go hand in hand with an evaluation of the effluents generated and discharged during this stage, so as to avoid merely swapping pollutants. Furthermore, the need to comply with both the international code ISO 14000 and local obligations to preserve the quality of water (in Brazil written into the Federal Constitution) make it essential to analyze the effluent from mechanical recycling. Therefore, on the basis of previous studies about which thermoplastics are present in greatest amounts in MSW [12, 25], the Residues Recycling Center, 3R-nrr, at Federal University of São Carlos (UFSCar) have conducted laboratory-scale tests to characterize the liquid effluent produced by the cleaning of the three plastics found in largest proportions in rigid plastic packaging residues, viz. PET and two polyolefins, high density polyethylene (HDPE) and polypropylene (PP). The polluting load of these effluents demonstrated that they were comparable to that of domestic sewage with a medium concentration of pollutants. No significant differences in the effluent characteristics were found between the two types of plastic studied, except for those differences intrinsic to the cleaning processes (temperature, surfactant, caustic soda

An Overview of Recent Advances and Trends in Plastic Recyling

15

concentration, pH) or arising from contamination of the plastics (oils and fats, solids). Generally speaking, these effluents would need to be treated before being discharged into bodies of water or even into sewage systems. Therefore, any plans for implementation of plastic recycling units should include an appropriate destination for such effluents in accordance with their final composition [57]. On the other hand, selective collection of these wastes proved to generate a much lower polluting load, as reported by Heyde and Kremer [58], indicating the importance of this type of collection since, among other advantages, it reduces the pollution deriving from the recycling process. Yet another advantage of selective separation of waste is that it reduces the need for and concentration of the cleaning agents used during recycling, thereby reducing its environmental impact and cost. Another aspect of the work performed in 3R-nrr is the use of the effluent characteristics to evaluate the process parameters in terms of cleanness efficiency. Good correlations were shown, since there is no addition of chemicals and all the performance was evaluated through only one batch [57, 59-61].

MECHANICAL RECYCLING As defined earlier, mechanical recycling is the process of converting discarded plastic into new products, principally by melting and molding. In this form of recycling, the macromolecular nature of the polymer is not destroyed, so that the degradation reactions that directly affect the physical and chemical properties of the polymer and, at times, its appearance, are minimized and controlled, irrespective of the processing method chosen. Nevertheless, chemical changes that occurred during the original processing and in-service use may have a negative effect on the quality of products reprocessed by mechanical recycling, in comparison with those manufactured from virgin resin. Mechanical recycling involves several steps, which generally include the following: collection, separation, grinding for large or thick objects or agglutination for films and thin objects, cleaning of the plastic to eliminate organic matter, drying (particularly important for polymers that are hydrolyzed) and reprocessing (Figure 2). Some of these steps are also important in chemical or energy recycling and may be taken out or added according to the needs of the material/object being recycled, the desired end-product and available conditions. The importance of the collection, separation and cleaning steps has already been mentioned. The stage of breaking into flakes or binding together, which normally occurs between separation and cleaning of the plastics, is mainly done to reduce the overall volume taken up by the plastic residues and to promote the interaction of those residues with the cleaning solution [62]. However, the size of the flakes produced at this stage may interfere with the cleaning efficiency, as the mass-transfer rate between the liquid and solid phases depends on the velocity gradient of the liquid near the surface of the flake [63]. Also, during extrusion of the plastic, depending on the system used, the size of flakes in the feed can be a hindrance to the feeding process [64].

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Sati Manrich and Amélia S. F. Santos

Figure 2. Complete recycling scheme (identification, separation and classification of different types of plastics (1); grinding (2); washing with or without addition of cleaning agents (3); drying (4); silos (5); agglutination (films and products with fine thickness) (6); extrusion (7); and granulation (8)).

After cleaning comes the drying step. This is mainly important in the subsequent reprocessing of molten polymers susceptible to hydrolysis and in the production of composites with inorganic fillers. The conditions chosen for drying depend, among other factors, on the type of humidity and the way it is bound to the material [65]. According to published work on this topic, there are three distinct kinds of moisture on recycled material: surface moisture, in the form of an external film, maintained by surface tension; freemoisture, which is inside nonhygroscopic materials, and bound moisture, either hygroscopic or dissolved, which exerts a lower vapor pressure than the pure liquid at the same temperature. Materials classified as hygroscopic are those that contain water in a homogeneous solution in the solid phase, whose vapor pressure is below that of pure water. In these materials, water is normally extracted by diffusion. However, if the water content exceeds the maximum hygroscopic content, so that part of the water is free, then until the latter water is removed the material will behave as a nonhygroscopic material. The drying conditions for hygroscopic solids are generally more aggressive than for others, since the lower the vapor pressure of the water, the higher its temperature of vaporization. By definition, the latter is the temperature at which the vapor pressure of the water is equal to the ambient pressure [66]. Consequently, drying processes for hygroscopic materials normally use high temperatures, with a supply of a suitable gas or a vacuum. The duration of this stage will depend on the temperature, the concentration gradient of water in the atmosphere, the relative velocity of the air, the residual humidity required and the pressure in the system. In vacuum drying, the concentration gradient and reduced vaporization point of the water, due to low pressure, are attractive features in view of the shorter time taken and the high quality of the end-product [66] if compared with other drying systems. Its chief benefit arises from the fast

An Overview of Recent Advances and Trends in Plastic Recyling

17

internal migration of the liquid resulting from the increased internal pressure gradient, which forces the water out to the edge of the material [67]. Finally, other factors affecting the drying time in hygroscopic materials are the size and shape of the particle and the degree of crystallinity. The bigger the particle, the larger is the path for water to migrate from the middle to the surface of particle. Conversely, the smaller the particle, the greater is the equilibrium water content, since the surface area available for absorption is larger [68]. Regarding crystallinity, the higher the proportion of crystalline phase in the polymer, the lower will be its final equilibrium water content. On the other hand, higher crystallinity also implies a lower diffusion coefficient of the water in the polymer matrix [68]. Owing to the first of these known correlations, commercial granules are normally sold in the crystalline state. Moreover, in polymers that crystallize relatively slowly, cold crystallization may occur alongside drying. In this case, especially if the recycled material contains flakes in the amorphous state, the drying is normally carried out with agitation or in a fluidized system, to prevent the particles sticking together because of the heat liberated during crystallization. After the water content has been reduced, the material proceeds to the remelting / restabilizing step, which directly affects the eventual quality of the end-product. At this point, the polymer mixture is formulated in accordance with the target application. Besides stabilizers, various other agents may be added to the polymer: reinforcements, other kinds of polymer, coupling agents, flame retardants [69], foaming agents [70, 71] and so on. Variations that have been employed to add more value to the recycled product and/or to widen its market niche include, for example, solid-state polymerization to recover the original properties of virgin PET, dissolution and reprecipitation to obtain high quality, very pure material [72, 73], electrospinning to make nanofibre from recycled expanded polystyrene (EPS) [74], civil engineering [75] and road construction [76] applications and synthetic paper. While all these initiatives are highly relevant to the goal of raising the fraction of waste plastic that is recycled, only a few will be described in more detail in this section.

Remelting-restabilization During reprocessing, it is necessary to limit the polymer degradation processes and thus guarantee its performance, to protect its added value. Degradation leads to molecular-weight variation, the inclusion of new groups in the polymer structure and undesirable changes in the appearance and properties of the material. Hence, this mechanical recycling step depends crucially on studying the degradation and restabilization behavior of recycled plastics. Some researchers have reported that, during reprocessing, thermoplastics exhibit the same processes of degradation as the equivalent virgin plastics, but accelerated. This occurs because of structural elements introduced by previous thermomechanical degradation, thermooxidation and photooxidation, and sensitized oxygenated chromophore groups that are products of oxidation. These elements affect both the susceptibility of the polymer towards further degradation and its miscibility with others. For this reason, polymer residues destined for mechanical recycling must not have been degraded to the extent that they have lost their original properties, nor can they contain high concentrations of sensitized oxygenated chromophore groups.

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During reprocessing, the polymer cannot be stabilized to block the oxidizing action of these groups, nor can a degraded polymer be transformed into a high quality recycled product, since its original rheological and/or optical properties cannot be recovered all at once [77]. Restabilization only ensures that the reprocessing is performed without a significant advance in the state of degradation and that the degradation mechanism proceeds at a much slower rate than would otherwise be the case. Another factor that contributes to the loss of stability of polymers while undergoing their first cycle of use is the consumption of protective additives in the materials during their production, service life and disposal. Thus, information on the resistance of recycled polymers to degradation, obtained by determining their susceptibility to oxidation and their residual stabilizer contents, would allow the stabilizing agents to be used more effectively and efficiently to block the advance of further degradation [78, 79].

Degradation Mechanisms Degradation occurs by various types of reaction classified as follows: thermal degradation, mechanical degradation, chemical degradation, photodegradation, biodegradation, thermomechanical degradation, mechanochemical degradation and photobiodegradation [78]. During reprocessing, the commonest types of degradation for most polymers are thermooxidation combined with mechanical degradation. In the special case of hydrolyzable polymers, hydrolysis is the predominant reaction and an extremely low residual water content is required, such as 20ppm (0.002%) for PET blow molding or injection molding. Oxygen acts as a catalyst of several types of degradation reaction, according to published evidence from various studies [80, 81]. In fact, the chromophore groups responsible for yellowing in PET are formed by thermooxidation reactions in the polymer [82-85]. Research carried out by the authors and co-workers indicates that the discoloration of PET can be accelerated by the relative humidity of air [86]. Hence, the temperature, the shear rate, the atmosphere and water content have significant effects on recycled plastic processing, in accordance with the type of polymer and its main mechanism of degradation. However, irrespective of the predominant mechanism, the initiation reactions that lead to free radicals being formed take place typically via cleavage of either the main backbone or branches of the polymer. During the propagation of polymer degradation, the following may occur [87]: −

polymer free radicals recombine to form crosslinks or branches. On the whole, this propagation reaction does not predominate, since such free radicals have low mobility in the polymer matrix (slow physicochemical process of diffusion) and only rarely will they recombine. On the other hand, polymers with occasional unsaturated groups (such as vinyl, vinylidene) in their structure may favor this type of reaction under certain conditions of temperature and oxygen content in the atmosphere and in the presence of specific additives such as peroxides [88]. The predominance of this reaction is reflected in a drop in the fluidity or melt flow index (MFI) and intrinsic viscosity of a solution of the polymer (reduction in the free volume of the polymer chains in dilute solution) and increases in the polydispersity (PD) and viscosity of the melt.

An Overview of Recent Advances and Trends in Plastic Recyling −

disproportionation of radicals to form linear products.

CH3 C CH2

Iniciator Iniciador

CH3

CH2

C CH2

C

CH3 +

CH3

H − −

19

CH (1)

liberation of monomers by depolymerization. chain reactions via free radicals in the presence of oxygen. These reactions are widespread and give rise to peroxy radicals (RO2•) (Eq.2), which readily remove hydrogen from the polymer matrix by forming hydroperoxides (ROOH) and other radicals (Eq. 3) [78]. In turn, the hydroperoxides, initial products of oxidative degradation of polymers, are easily decomposed by heat or light (at near-UV wavelengths) to alkoxy (C-O•) and hydroxyl (OH•) radicals, since the O–O bond is weak.

C O2

C + O2

(2)

H C O2

+

C

kr

C OOH +

C (3)

As a result of the action of the disproportionation and chain reactions promoted by free radicals in the presence of oxygen, the proportion of high-molecular-weight polymer chains is observed to fall, resulting in reduced viscosities of both the melt and the polymer solution and a narrowing in the molecular-weight distribution (MWD) [88]. Polymers are thought to have a critical molecular weight (Mc), below which they become brittle. Among polyolefins, this is generally assumed to correspond to the point during degradation when the number average molecular weight ( M n ) has fallen to around half of the original value [87]. Some authors claim it can be taken to be in the region of 10 kDa. For example, polycarbonate has an estimated Mc of 14 kDa and for polyamide 11, Mc = 15 kDa [89]. This critical value relates to the fact that scission of the polymer chain is confined to the amorphous regions and tie segments that connects the amorphous and crystalline regions. As consequences of chain scission in amorphous phase, the stress transmitted between adjacent crystalline zones decreases dramatically reducing the elongation at break. Additionally, the chain segments released from previously entangled regions are allowed to crystallize, causing a rise in the density (crystallinity) during oxidation. This last phenomenon, known as chemicrystallization, may lead to the formation of surface fissures, which act as stress concentrators during elongation under tension or flexure [87].

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Sati Manrich and Amélia S. F. Santos

Finally, processes that terminate degradation can occur either by the recombination (branching and/or crosslinking) or dissociation (chain scission) of free radicals, thus transformed into inert or stable products. If the dominant reaction is recombination, there will be a rise in the thermal distortion temperature and the creep and softening points, simultaneously with reductions in flexibility and in the elongation at break of the polymer [87]. Conversely, if dissociation predominates, there will be a fall in M n and in the breaking tension. It follows that the type of reaction prevailing during degradation is what determines the eventual properties of the compound or polymer. Concerning the kinetics of polymer oxidation, the rate of these reactions depends on a series of factors, apart from the structural properties of the polymer previously commented, including the duration of oxygen absorption, the oxygen content in the polymer, pressure, action of light, temperature and traces of transition metals. These reactions also characteristically exhibit induction periods, are self-catalyzing and can be inhibited or retarded with additives [87]. The reaction rate of oxidation (Eq.2) is controlled mainly by the direct attack of oxygen at the most vulnerable sites in the various chemical structures of the polymer, such as the immediate neighborhoods of unsaturated bonds or tertiary carbon atoms [78, 87]. The probability of these initial reactions to occur is higher when the polymer has more reactive hydrogen. A classic example of this is the lower oxidation stability of polypropylene (PP), compared to high-density polyethylene (HDPE), due to the presence in PP of a larger number of tertiary carbons. Thus, PP is rarely used without antioxidants. The decomposition of hydroperoxides can be accelerated by traces of metals (Zn, Ti, Fe, Cr, Cd, V, Al and Cu from cable insulators, etc.), originating from impurities, pigments and residues of catalysts (polyolefins), acid residues (chlorine from TiCl3, AlR2Cl or MgCl2), fillers and antistatic agents. The catalytic power of the transition metals can be put in the following order: Ba < Mg < Al < Ti < Ni < V < Fe < Cr < Co [90]. These impurities can allow oxidative degradation of the polyolefins by chain scission to occur at lower temperatures (< 150°C), if the number of unsaturated groups is minimal ( 0.2 ωt%), such as diene terpolymers, e.g. ethylenepropylene-diene elastomers (EPDM), crosslinked networks can be formed at low temperatures (90%, energy consumption 3,000 kWh/ton to produce a smooth, coherent, perfect sheet which was easily strippable. A flow sheet has also been developed for zinc oxide production from zinc ash with zinc content of 60-80% along with other impurities like Fe, Cu and Pb for a private party in Kolkata. The unit operations involved are dissolution of zinc ash, purification of leach liquor, preparation of zinc hydroxide/carbonate mixture and finally zinc oxide by controlled heating of this hydroxide/carbonate. The purity of ZnO is comparable to international standard [56]. Recently the drum filter cake(DFC) generated from zinc industry(Composition SiO2: 2055%, Fe: 5-20%, Al: 5-25%, Pb: 1-5%, MnO2: 1-10%) was used to prepare frit/glaze for ceramic industry[57] at RRL Bhopal. Silica present in DFC acts as glass former and lead as a flux for glass formation. Toxic leadgets complexed in the glass matrix to make the product non hazardous. The product was tested for its toxicity following TCLP test[57]. National Metallurgical Laboratory, Jamshedpur is actively involved in developing both pyrometallurgical as well as hydrometallurgical processes to recover zinc from zinc dross/ash and other residues. There are no efficient pyro/ hydrometallurgical processes available in India to treat the zinc dross and Effluent Treatment Plant (ETP) sludges without generating solid waste for disposal. Production of zinc oxide from ash by ammoniacal route developed earlier at NML has been found to be technically competitive to the sulphuric acid route [58]. A direct electrowinning process to recover zinc as zinc powder from an alkaline electrolytic bath is being developed on laboratory scale. The process requires less number of steps and is thus expected to be energy efficient. Zinc recovery from the dross by distillation process has been developed recently at NML with 90% overall recovery, from the dross produced in the galvanising plant of TATA STEEL.[24, 59-61]. From the environmental point of view, lead recovery from battery sludge via hydrometallurgical and electrowinning processes looks attractive. But none of the abovedescribed processes have become operational and only a number of pilot plant trials have been conducted. Some processes developed are at laboratory scale only. A full-scale lead hydrometallurgical and electrowinning plant need to be operational in the coming century to build the confidence among the lead producer and to reduce environmental impacts. Use of cupola for lead recovery from battery scrap is also being developed in NML. R&D work related to the lead recovery from spent acid batteries is also being carried out at CECRI, Karaikudi. A novel direct electrochemical reduction technique has been developed for the production of lead powders from spent lead acid batteries [1]. Binani industries is setting up an integrated battery-recycling unit in Wada, Thane District of Maharashtra, which would be implemented in two phases. The first phase was planned be for the manufacture of 25,000MT of secondary lead while the second phase was for the manufacture of 125,000MT of Primary Lead with imported Lead Concentrates. The plant would be one of India's first modern lead recycling plants. ENGITEC Technologies of

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Italy will provide the technical know- how for the manufacture of lead. This technology is not only environment friendly but also has some of the best safety measure in the industry. The recycling facility will also yield sulphuric acid and polypropylene as by-products. Manufacturers of lead-acid batteries, pigments, lead oxide and submarine cables would be the main users of the lead. In order to fix the limits of toxic elements in Zinc ash/skimming an effort was made at NML, based on the data available for head analysis and TCLP tests of several samples and recommended tentative threshold limits (Table 13) of metal components in zinc ash/skimming for import/export purposes. Based on the recommendation Ministry of Environment and Forest permitted import of zinc secondaries to a number of recycling units possessing necessary processing technology and waste handling and disposal expertise/facilities, in the overall interest of the nation. Table 13: The tentative limits fixed for toxic elements in zinc ash for imports Sl. No. Components 1 Zn Cu 2 As 3 4 Cd 5 Cr 6 Pb 7 Ba Hg 8 9 Se Work done at NML for MoEF.

Percentage 60 (min.) 1.7 (max) 0.1 (max) 0.1 (max) 0.01 (max) 1.25 (max) 0.005 (max) 0.002 (max) 0.004 (max)

CONCLUSION Most of the pollution control technologies adopted today convert the pollutant from one form to other like in effluent treatment plant aqueous pollutant may be converted into solid waste which is discharged either in open or secured landfill. Both are undesirable from the land point of view, which need to be preserved for future generation. As the leachate generating from the dumping of these hazardous wastes contaminates the environment, efforts must be directed towards not only effectively monitoring and managing the environment but also developing and applying viable and acceptable ecofriendly processes and waste handling/management technologies to cater to the pollution free environmental control of even the small and medium scale industries. −

Main source of raw material for secondary zinc plants in India is imported ash/dross as they are not available Indigenously. Thus all those units having proper pollution control devices, eco-friendly process technology and legal permission from Ministry of Environment and Forest (MOEF) can import zinc bearing raw material. From environmental point of view secondary zinc recovery process is technologically

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−

−

− −

−

acceptable in India. Basel ban restricted the import of zinc ash, skimmings, drosses contaminated in plenty with several toxic elements. Various processes developed indigenously for secondary raw materials are running successfully at different parts of the country. There are some processes ready for commercialization and some are in developing stage. Collection and recycling of spent acid battery is the major cause of concern, which has not been achieved to a satisfactory level as compared to developed nations. A legislation as well as appropriate monitoring are to be evolved and enforced for a systematic collection and it’s recycling in the units having eco-friendly and waste management process technologies. The slags produced from the primary and secondary lead processing industries must be disposed off to the sites as per specification/instructions laid down by the Pollution Control Boards. Development of low cost and eco-friendly technology should be encouraged in order to sustain the recycling operation, which will not only meet the increasing demand of lead but also conserve the raw materials. For battery recyclers, pollution control boards must organise awareness programmes with respect to handling, transport and recycling of battery scrap. The existing wastes generated and accumulated from various nonferrous process industries over a long period should be characterized (TCLP and water extract) for its hazardous or non-hazardous nature and a procedure has to be evolved in consultation with industry and CPCB/SPCB/different laboratories for its safe disposal. In addition to increased utilisation of solid wastes, efforts are needed towards waste minimisation by attacking the problem at its source, which not only maximise production and product quality, but also minimise the overall environmental impact by: technology upgradation/use of eco-friendly technology, improvement in the quality of raw material, audit on waste minimisation, adopting innovative management strategies, conducting employee awareness programme.

ACKNOWLEDGEMENTS Authors wish to thank the Director, NML, Jamshedpur for giving permission to publish the paper and the Ministry of Environment and Forest (MoEF), New Delhi for financial support. Thanks are also due to the management of various industries for supplying the required information.

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In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 155-195 © 2006 Nova Science Publishers, Inc.

Chapter 5

RECYCLING OF WASTES (AGRICULTURAL RESIDUES AND USED TIRES) FOR ACTIVATED CARBON PRODUCTION A. A. Zabaniotou∗ Department of Chemical Engineering, Aristotle University of Thessaloniki Thessaloniki, Greece

ABSTRACT A review of the production of activated carbons from wastes, such as agricultural and used tires, by using atmospheric pyrolysis, is presented. Pyrolysis of waste is a CO2neutral process and can transform biomass to energy and materials. It is a possible way for chemical recycling of the organic matter. This study evaluates pyrolysis of olive kernels, olive wood, and cotton ginning waste and used tires, by studying the effect of temperature on the pyrolysis product yields and investigates production of activated carbon from pyrolytic char. A comparison in characteristics and uses of activated carbons from agricultural residues and tires with commercial carbons have been made.

Keywords: Pyrolysis; Activation; Agricultural residues; Used tires; Activated carbon

INTRODUCTION Agricultural waste is a form of biomass, which is readily available but not largely utilized in recovery schemes. Over the past decade, the biomass utilization field has been driven largely in response to oil supply disruptions and the challenge of meeting the Kyoto agreement on global warming. Biomass can play a dual role in greenhouse gas mitigation,

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both as an energy source to substitute fossil fuels and as a carbon sink. Biomass products are sustainable. The green plants from which biomass products are derived fix carbon dioxide as they grow, so their use does not add to the levels of atmospheric carbon. In addition, using residues/refuse as a source for energy and materials avoids polluting landfill disposal or combustion gases. Agricultural residues are among the major EU energy resources [1]. The potential of the available biomass in the form of agricultural wastes is sufficient for the supply of a big percentage of the energy demands regarding production, and have proved to be promising raw materials for the production of activated carbons [2, 3]. Literature survey indicates that there have been many attempts to obtain low-cost activated carbon or adsorbent from agricultural wastes such as wheat [4], corn straw [4], miscanthus [5, 20], sunflower shell [6], pinecone [6], rapeseed [6, 12], cotton residues [6, 10, 89], olive residues [5, 6, 20, 29, 30, 31, 32, 33, 34, 55,], almond shells [2, 22, 24], peach stones [9], grape seeds [2], straw [5, 11, 20], oat hulls [8, 13], corn stover [8, 13], apricot stones [2, 22], cherry stones [2], peanut hull [28], nut shells [2, 16, 17, 18, 23], rice hulls [21], corn cob [9 ,14, 15, 19] corn hulls [13], hazelnut shells [22], pecan shells [21], rice husks [26, 28] and rice straw [21, 25]. Agricultural residues are difficult and expensive to collect but they are available and at a low price [1]. Pyrolysis is one form of energy and material recovery process, which has the potential to generate char, oil and gas product [10]. Because of the thermal treatment, which removes the moisture and the volatile matter contents of the biomass, the remaining solid char shows different properties than the parent biomass materials. These changes in the properties usually lead to high reactivity, and hence, an alternative usage of char as an adsorbent material becomes possible [10]. Pyrolysis of the above residues, under a non-oxidizing atmosphere or gasification in-situ with energy or alternative fuels production could be a solution to the environmental problem that landfilling or combustion could create and furthermore, can establish a new approach for a more efficient utilization of biomass and wastes [3]. Fuels derived from biomass contain less sulfur. Pyrolysis, offers an environmentally attractive method of reducing the waste. Properly designed systems using local biomass can also reduce other atmospheric pollutants, and thus improve local air quality. Using residues will also improve the local environment; while in the same time can generate jobs, and improve rural economies and help maintain agriculture. Unlike incineration, the pyrolysis process does not lead to air emissions given that everything takes place within a closed system. One exception is the produced gas, which is mainly composed of methane and hydrogen and can be used in power production on site, or be burned in nearby boiler plants. Unwanted gasses, like SOx and NOx, are not developed in the pyrolysis process because the process is carried out without oxygen [31, 32, 33, 37]. The solid product of pyrolysis, named char, can be activated and produce active carbon, a high value added product. With the parallel use of char as feedstock for material production, the shorter term targets set out in the White Paper of EU could be reached; because optimization of use of the agricultural residues can be achieved and cost –effective integrated approaches can be developed. The char is an attractive by-product, with applications including soil amendments and production of activated carbons, which is useful as a sorbent for air pollution control as well ∗

Tel. 0030 2310 99 6274, Fax. 0030 2310 99 6209, E-mail : [email protected]

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as for wastewater treatment [8] and concern many industries as diverse as food and beverage processing, chemical, petroleum, mining, nuclear, automobile and vacuum manufacturing [35]. In fact, activated carbon has some of the strongest physical adsorption properties of any material even known [36] because of the highly microporous form with both high internal surface area and porosity. They often serve as catalysts and catalyst supports [9]. They are widely used for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were [35].

Olive Residues In Mediterranean basin countries olive cultivation is a typical activity. However, residues from olive plantations are hardly used as a renewable energy source. As pointed out in the literature [29, 30, 31, 32, 33, 34, 93] only few studies have dealt with olive residues, although olive residues could be a source for fuels, energy generation and activated carbon production. Proper management and exploitation of this potential could lead to economically profitable approximations and solutions for the agricultural industry Using residues will also improve the local environment; while in the same time can generate jobs, and improve rural economies and help maintain agriculture [1].

Cotton Ginning Wastes Waste management is a significant problem facing the cotton ginning industry. The ginning of one lint bale (227 kg) of spindle harvested seed cotton generates between 37kg and 147 kg of waste. The disposal of wastes associated with the processing of cotton is posing increasing problems. Traditional disposal methods, such as open-air incineration and landfilling are no longer adequate due to increasing environmental concerns. About 17.1 million bales of cotton were ginned in the United States [48] and the estimated cotton gin waste was 2.25Χ109 kg. Cotton gin waste (CGW) consists of sticks, leaves, burs, soil particles, mote, cotton lint, and other plant materials [49]. Slight differences in the proportions of the components are usually found between varying mechanical harvest methods .The traditional methods of CGW disposal include incineration, landfilling, and incorporation into the soil. The most recent directives further restrict particulate matter discharge into the atmosphere, thus eliminating incineration as an option for small cotton gins. Furthermore, because of the high ash content of the feedstock, there could be potential slagging problems associated with large-scale incineration. Landfilling is not a viable option because tipping fees are very high. The current method of choice is the incorporation of the waste into the soil, an option that is unsuitable for the climatic conditions of some countries. There is much concern over the presence of weed seeds, insect infestations, diseases, and excess chemicals in the waste that may degrade the receiving land. The conversion of CGW to value-added products has not been extensively studied. Brink [50] and Beck and Clements [51] studied the conversion of CGW to ethanol and concluded that 142.8lt ethanol per tonne could be produced from this feedstock.

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Cotton gin waste was collected from a cotton ginning plant in Virginia and characterized before and after steam explosion to evaluate its potential applications for higher value products such as ethanol by [92]. Griffin [52] and Schacht and LePori [49] analyzed cotton gin waste to assess its fuel value for combustion. These researchers proposed using the feedstock for the production of char, hydrogen, protein, and pyrolysis gases. Parnell et al. [53] investigated the gasification of cotton gin waste in a fluidized bed reactor. The gas produced had a low heating value and the projected net revenue from the process was very low. However, activated carbon produced from the gasification of the feedstock was found to be cheaper, but less effective than those produced from conventional carbon sources [54].

Used Tires Another abundant worldwide waste is used tires. Recently because of environmental lows and because used tires are in enormous supply, they have been the object of study by chemical and environmental engineers. It would seem that any step in the direction of economical utilization of an otherwise disagreeable waste material is a positive contribution to the protection of the environment. Potential commercial applications of tire-derived activated carbons for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were studied by researchers [36]. Used tires represent a considerable quantity of solid wastes. Traditional disposal methods such as open-air incineration and landfilling are no longer adequate to increasing environmental concerns. Because used tires contain appreciable energy content, thermal treatment is considered an interesting disposal solution. Potential reuse of the polymeric contents of tires has received considerable attention. Processes have been evaluated for production of goods such as construction fillers; however, fillers and other reclamation applications have shown relatively small economic potential. Among the thermal treatment processes, pyrolysis has received increasing interest, as an alternative method to obtain raw materials and fuels [38]. Pyrolysis might be used for char production. The solid char may be used either as smokeless fuel, carbon black or for preparation of activated carbon. One of the alternative recovery methods applied of used tires is the Energy recovery in process/incineration plant: This treatment cannot really be characterized as recycling, but is the exploitation of the energy within the rubber mass. Energy recovery is recognized as equal to material recycling in the waste management hierarchy. Incineration solves a waste problem and reuses the waste as energy. However, advanced cleaning technology/filters is required to satisfy emissions to air requirements. The cement industry is today the largest recipient of used car tires, and it has become somewhat common to use automobile tires as a replacement for some of the coal in cement kilns [38]. Another alternative method is the Retreading which is a reuse and should be a proper method of taking care of resources. The life span for the tire cores would be doubled at minimum, and the total waste volume would be reduced. The retreading process, however, leads to rubber waste in the form of powder, and the retreaded tires will eventually return as waste. For this reason, retreading cannot be considered a final solution to the problem [38].

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Grinding to Powder/Granules is a method of transforming the tires into a saleable raw material. A possible market for this material can also be created, for example as an additive to road surfaces. From an environmental perspective, this use of rubber powder is not ideal, given that wear will eventually cause the rubber to spread uncontrollably into nature, although this problem is most likely small in comparison to the total spreading of asphalt dust. It is also possible to find other uses for rubber powder and granules as raw materials. The economics of these other uses is uncertain [38]. The process of interest is the pyrolysis of tires to produce liquid hydrocarbons and gases with high calorific values. Pyrolysis has studied by others researchers and data have been reported in the international literature [38, 39, 40, 41, 42, 43, 44]. Pyrolysis yields solid char residues which generally contain higher amounts of elemental carbon than the original tires. Most studies on conversion of tire char to activated carbon rely on further pyrolysis at 600850ºC under nitrogen atmosphere followed by activation with acid for reaction with superheated steam. All of the processes are energy intensive. Since tires are made mostly of rubber, the re-use of their carbon content in the form of activated carbon can be very rewarding. This form of carbon is a commercially important adsorbent of noxious materials in (for example) flue gases and/or waste steam. In adsorbing these toxics, carbon attaches them more or less firmly to its highly porous surfaces, which are very large. When the carbon is removed from the system it takes the impurity with it. Typical adsorbates are acetone, trichloroethane, and compounds of mercury. All are toxic in some degree and any or all may be found in flue gases from power plants. But tires are anything but biodegradable: they are designed and built to resist the ravages of the environment. As a result these piles of discarded tires remain year after year to spoil the appearance of the countryside. Any substantial new use for old tires can reduce and perhaps eliminate at least one source of pollution and marring of the landscape [45]. To reduce the negative environmental impacts by tires disposal in landiffils or by incineration, pyrolysis could be applied. Unlike incineration, the tires pyrolysis process does not lead to air emissions given that everything takes place within a closed system. One exception is the produced gas, which is mainly composed of methane and hydrogen and can be used in power production on site, or be burned in nearby boiler plants. Unwanted gasses, like SOx and NOx, are not developed in the pyrolysis process because the process is carried out without oxygen. Nevertheless, tires contain a significant amount of sulfur from vulcanization; however, after treatment, the majority of the sulfur remains as solid sulfides together with the carbon. The sulfides can be separated out through acid washing. Because the process allows for accurate control of temperatures in all phases, the resulting carbon will be of high and controllable quality. It can be further refined to a standard trading commodity with high market value [39, 40, 46, 47]. Because old tires are in enormous supply, they have been the object of study for some time by chemical and environmental engineers and associations [91]. Their most recent publications of research results, supported by both public and private funds, describes the direct production of activated carbon from waste tires by a relatively simple process, and shows that it is "within the ball park" as an effective adsorbent when compared with carbon from standard commercial sources [45]. The absorbency of the carbon was measured and found to be generally about half that of commercially available activated carbons [45]. In view of the extremely low cost of the discarded rubber, the economics of the process seem promising in competition with the

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standard commercial types. It would seem that any step in the direction of economical utilization of an otherwise disagreeable waste material is a positive contribution to the protection of the environment. Potential commercial applications of tire-derived activated carbons for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were studied by the researchers. In these tests, the performance of the tire-activated carbon was comparable or superior to some commercial carbons. The present study reviews the current state of the production and characterization of activated carbons from agricultural wastes and used tires by using pyrolysis under atmospheric condition, as the recycling method. The aim of this study is to investigate the conversion of some of these abundant wastes, into high-quality activated carbons, under atmospheric conditions, that might be commercially viable. The experimental work, described in the present paper, includes: a) experimental and analytical work on pyrolysis, activation and characterisation of the carbons in laboratory scale and b) evaluation of findings and comparison of results with commercial active carbons.

USES OF ACTIVATED CHAR Activated carbons find application in processes both in the gas and liquid phase and their pore structure must be determined by combining gas and liquid-phase adsorption. Further the two methods give complementary information on porosity configuration. Therefore characterization of activated carbons has been mainly focused on determinations of surface area and pore size distribution by N2 adsorption at 77 K and adsorption of methylene blue from aqueous solutions. [55] Activated charcoal has been in use for centuries as an air/water purifier, health supplement and chemical 'scrubber', in fact activated carbon has some of the strongest physical adsorption properties of any material even known. Activated charcoal, also known as 'activated carbon' is made by burning hardwood, nutshells, coconut husks, animal cones and/or other carbonaceous materials. The charcoal becomes 'activated' by heating it with steam to high temperature levels in the absence of oxygen. This removes any non-carbon elements and produces a porous internal microstructure with an extremely high surface area. A single gram of a high quality activated charcoal can have 400 - 2000 m2 of surface area, 98% of which is internal. The actual active surface area, characteristics and performance of a particular activated carbon source depends largely on the nature of the material it was manufactured from and the process by which it was 'activated'. It is this huge surface area of activated charcoal where the unwanted molecules are adsorbed and trapped. Adsorption means the impurities in the air are attached to the surface of the activated carbon by a chemical attraction. When certain chemicals pass next to the carbon surface they attach to the surface and are trapped. Absorption is incorporation into the carbon's structure through pores, this occurs before the process of adsorption. Activated carbon can adsorb an extremely wide spectrum of adsorbates. This is because activated carbon has different types and/or sizes of pores within its internal structure.

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Activated carbon manufactured from coconut husk [87], has one of the largest activated surface areas combined with a high percentage of micro pores in the size range 5 - 10 Ao (Angstoms), making it ideal for removal of odorous compounds, gases from volatile organic compounds (VOCs), and gases of a low molecular weight. Removal of gases, originating from volatile organic compounds, is important in many different situations, as these come from organic chemicals that have a high vapor pressure and easily form vapors at normal temperatures. Many industrial and consumer products ranging from office supplies, building materials and in particular many plants, trees and micro-organisms such as bacteria, produce volatile organic compounds and activated carbon is the most effective way of removing these from the air. For this reason activated charcoal manufactured from coconut husk is used in a wide range of air purification systems from fume hoods, respirators, gas masks, cooker hoods and air purifiers for indoor gardening. Where indoor air quality is being compromised by odors and gases from volatile organic compounds, air filtration with coconut husk activated carbon is the safest and most effective way of dealing with the problem [87].

CHARACTERISTICS OF WASTES Agricultural residues are produced in huge amounts worldwide, their proximate and ultimate analysis are presented in Table 1 and 2. However, the composition of those materials differs significantly from woody biomass composition and the difference in gas composition would be due to the difference in the component composition of the feedstock. Therefore, fundamental search regarding the effects their composition on active carbon production is important in attempts to obtain a desirable product. It is imperative to have pre-normative research in order to investigate the influence of their composition on the products. Table 1. Agricultural residues availability, proximate and ultimate analysis Agricultural Wastes

Olive tree prunings Cotton stalks Durum wheat straw Corn stalks Soft wheat straw Vineyward prunings Corn cobs Sugar beet leaves Barley straw Rice straw Peach tree prunings Almond tree prunings Oats straw Sunflower straw Cherry tree prunings Apricot tree prunings

Moisture (%ww) 7,1 6 40 0 15 40 7,1 75 15 25 40 40 15 40 40 40

Ash (%ww) 4,75 13,3 n.a 6,4 13,7 3,8 5,34 4,8 4,9 13,4 1 n.a 4,9 3 1 0,2

Volatiles C H O N S HHV (%ww) (%ww,) (%ww) (%ww) (%ww) (%ww) (Kcal/Kg) n.a 49,9 6 43,4 0,7 4500 n.a 41,23 5,03 34 2,63 0 3772 n.a n.a n.a n.a n.a n.a 4278 n.a 45,53 6,15 41,11 0,78 0,13 4253 69,8 n.a n.a n.a n.a n.a 4278 n.a 47,6 5,6 41,1 1,8 0,08 4011 n.a 46,3 5,6 42,19 0,57 0 4300 n.a 44,5 5,9 42,8 1,84 0,13 4230 n.a 46,8 5,53 41,9 0,41 0,06 4489 69,3 41,8 4,63 36,6 0,7 0,08 2900 79,1 53 5,9 39,1 0,32 0,05 4500 n.a n.a n.a n.a n.a n.a 4398 n.a 46 5,91 43,5 1,13 0,015 4321 n.a 52,9 6,58 35,9 1,38 0,15 4971 84,2 n.a n.a n.a n.a n.a 5198 80,4 51,4 6,29 41,2 0,8 0,1 4971

The nature and characteristics of the feedstock plays an important role in the design of a thermochemical conversion system. The main characteristics concerning the applicability of

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various wastes in the thermochemical processes are the ash content, density, and particle size. For example, cotton gin waste has different characteristics than other types of biomass examined up to now and therefore research on the waste composition and product yields is necessary in order to avoid operational problems. Table 2. Literature review of agricultural residues pyrolysis for active carbons production Agricultural Residue Wheat Corn straw Corn cob Corn hulls Corn stover Olive residues and olive kernel Straw Birch Sugarcane bagasse Miscanthus Sunflower shell Pinecones Radiata Pine Rapeseed residue Cotton residues Eucalyprus Apricot stones Cherry stones Grapeseeds Nut shells Pistachio shells Macademia nut shells Hazelnut shells Peanut hulls Almond shells Oat hulls Oak Rice straw Rice husks Pecan shells Casava peel

Particle Size (µm ) 100 100 119 – 200 n.a n.a. 125 – 250 597 n.a. 100 – 200 n.a. 250 250 100 - 200 250 n.a. 100 - 200 20 - 125 20 – 100 20 - 100 20 – 100 200 - 280 212 - 300 100 - 125 20 - 200 100 10 – 20 ,12-40 mesh -//-

Reference 1 1 7,3,14 11 6,11 2,12,20 2,9,20 2,20 2,4,20,21 2,20 3 3 4 3 3,8 4 5, 22 5 5 15, 17 16 16 18 5,22,23,24 6 11 21 21,26,28 21 51

Cotton gin waste physical properties (density, particle size and shape, ash content) and heating value indicate that it is different from other biomass residues, especially wood therefore much more attention is needed in the design of the conversion process. Cotton gin waste is very loose compared to other biomass material. Its bulk density is about 25 kg/m3, which is even lighter than the straw waste (40-50 kg/m3), [57]. This could influence the steady steadiness of the operation of the reactor in the thermochemical conversion. If

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gasification is used as method for valorization, it is important to have steady state conditions. Due to the nature of the material, it may be difficult to have smooth fluidization operation and hence smooth continuous operation of the reactor. Cotton gin waste particle size and shape are not uniform. This might pose another operation problem of the gasifier. The ash content of the cotton gin is rather high (15wt. %), much higher than wood residues (Table 10). Therefore direct combustion of cotton gin wastes for a boiler operation will not be usually satisfactory, leading to severe ash fouling, intensified slogging and corrosion, necessitating frequent maintenance. Used tires are another type of solid wastes. Tires may be composed of various rubbers, such as natural rubber (NR), butyl rubber (BR) or styrene - butadiene rubber (SBR) [46]. The most commonly used tire rubber is styrene - butadiene copolymer (SBR), containing about 25 wt% styrene [47]. A typical composition for tire rubber is shown in Table 3. In Figure 1 all possible alternatives uses of used tires pyrolysis products is presented. Table 3. Typical tire composition Component

Wt% 62.1 31.0 1.9 1.9 1.2 1.1 0.7 99.9

SBR Carbon Black Extender Oil Zinc Oxide Stearic Acid Sulphur Accelerator Total

GAS

USED USED TYRES TYRES

PYROLYSIS PYROLYSIS

OIL

RECYCLE TO RUBBER MATERIALS PRODUCTION (Fenders, footgear, belts)

BOILER FUEL

ACTIVE CARBON (Water purification, Air purification, Special applications etc.)

CHAR

SOLID FUEL Co-combustion With other Solid fuel

GASIFICATION

BOILER FUEL Steam, CO2 SYN-CAS Raw materials for the Chemical Industry

Steam, CO2

Figure 1. Alternatives uses of used tires pyrolysis products.

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PROCESS LITERATURE OVERVIEW Pyrolysis Bibliographic survey has revealed many papers dealing with all kind of agricultural residues pyrolysis. Tables 4(a-q) present some pyrolysis and activating conditions for the production of carbons from agricultural residues. Pyrolysis temperature has the most significant effect - followed by pyrolysis heating rate, the nitrogen flow rate and then finally the pyrolysis residence time. Generally, increasing pyrolysis temperature reduces yields of both chars. According to Ayse E. Putun et.al., [10], increased temperature leads to a decreased yield of solid and an increased yield of liquid and gases. As the temperature is raised, there is a rise in ash and fixed carbon percentage and there is a decrease in volatile matter. Consequently, higher temperature yields charcoals of greater quality. The decrease in the char yield with increasing temperature could either be due to greater primary decomposition of biomass at higher temperatures or through secondary decomposition of char residue. The secondary decomposition of the char at higher temperatures may also give some non condensable gaseous products, which also contributes to the increase in gas yield, which is parallel to the increase in temperature of pyrolysis. Indeed, as the temperatures of primary degradation are increased or the residence times of primary vapours inside the cracked particle has to stay shorter, the char yields decrease [10]. Temperature also has studied of W. T. Tsai et.al. [9, 14]; it was noticed that char yield decreases with temperature, for preparation of activated carbons with chemical activation (ZnCl2), where. Corn stover with oat hulls for char production by Thermogravimetric analysis (TGA), was studied by M. Fan et.al., [8]. There was no pre-treatment prior to fast pyrolysis that was held in a nitrogen fluidized bed reactor. Table 4h presents details about pyrolysis conditions. More details about TGA conditions are presented in Table 4i. [8]. T.Zhang at al. [13], studied oak wood wastes, corn hulls and corn stover carbonization in a fluidized bed reactor at 500oC, Table 4j. In the study of H. Haykiri-Acma et.al [6]., TGA analysis was used to pyrolyse and then gasify chars obtained from sunflower shell, pinecone, rapeseed, cotton and olive residues pyrolysis, Table 4b. Obtained chars were heated in order to gasify under steam and nitrogen atmosphere and in equal volumetric ratio. For pinus radiate, eucalyptus maculate and sugar cane bagasse, atmospheric reactivity measurements were performed under isothermal conditions, using a thermogravimetric analyser [7], Table 4k. Sugarcane bagasse, rice hulls, rice straw, and pecan shells were also studied, [21], Table 4l. Table 4a. Olive, straw, birch, bagasse and miscanthus pyrolysis and activation conditions [5, 20] (one-step process). Activation conditions, T(oC/ h) 750/2 (10oC/min)

Activating agent steam/CO2

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Table 4b. Pyrolysis -TGA analysis conditions for sunflower shell, pinecoke, rapeseed, cotton and olive residues [6] (gasification up to 1000oC after pyrolysing). Feed rate (mg)

Gas flowrate (s)

Duration (hr)

n.a.

N2 / 40 ml/min

1,5

Temperature PROGRAMME Tambient – 1000 oC

Table 4c. Pyrolysis and activation conditions of apricot stones, [2, 22] (one-step process). References [2] [22]

Temperature / duration (oC/ h) Activating agent 800/ 1h steam 800/1h chemical (ZnCl2)

Table 4d. Pyrolysis and activation conditions of cherry stones, grape seeds and nutshells, [2] (one-step process).

Temperature / duration (oC/ h) 800/ 1h (15oC/min)

Activating agent steam

Table 4e. Pyrolysis and activation conditions of Pistachio-nutshells, Hazelnut shell and Macadamia nutshell, [16, 17, 18, 22]. References Raw material

[16] [18] [17]

[22]

Charring conditions Activation Activating (oC/ h) carbonization conditions (oC/ h) agent o Pistachio-nut 500/2 (10 C/min) 900/ 30min physical CO2 shells (10oC/min) Pistachio-nut 500/2 800/2.5 (10oC/min) physical CO2 shells Macadamia 1h 500 chemical nutshell (ZnCl2) 1h 800 chemical (KOH) Hazelnut shell 750/10 chemical (ZnCl2)

Table 4f. Pyrolysis and activation conditions of peanut hulls, [28]. Charring conditions (oC/ h) carbonization 500/2 -

Activation conditions (oC/ h) 700-900 600/2 300-750/6 500-700/3 500/3-6

Activating agent physical pure steam chemical (ZnCl2) chemical (KOH) chemical (H3PO4)

Additional information two-step process one-step process one-step process one-step process one-step process

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A. A. Zabaniotou Table 4g. Pyrolysis and activation conditions of almond shells, [2, 22, 23, 24].

References

Charring conditions (oC/ h) carbonization

[22] [23]

n.a.

[2]

800/ 1h (15oC/min)

[24]

400/1

Activation Activating conditions (oC/ h) agent 750/10 chemical (ZnCl2) n.a. chemical (H3PO4) 800/ 1h steam

Additional information

one-step pyrolysis/activation physical different samples (either with CO2 or N2)

850/1

Table 4h. Pyrolysis conditions for corn stover with oat hulls [8] Pyrolysis Temperature (oC) 500

Residence time (s) 1,5

Particle size (µm) >1, from which equation 1 reduces very nearly to (P/Pa)/V{1-(P/Pa)] = (1/Vm) (P/Pa)

(3)

which rearranges to Vm = V[1-(P/Pa)]

(4)

Another way of arriving at the same result is by recognising that the term 1/(VmC) of equation 1 is generally small. Taking it as insignificant changes the slope, and hence the value of Vm and the sample surface area as calculated by equation 2, only a small amount. Equation 1 can be rearranged with the contribution of the intercept term taken to vanishingly small to give also Vm = V[1-(P/Pa)]

(5)

Substituting equation 5 into equation 2 yields S= VAN [1-P/Pa]/M From which the sample surface area is readily determined once the volume V of gas adsorbed (or desorbed, which must be identical) is measured and appropriate values for the other terms are incorporated. For nitrogen gas adsorbed from a mixture of 30 mole % nitrogen and 70 mole % helium using a liquid nitrogen bath, the values are arrived as follows: −

− − −

The volume V of gas with which calibrates the FlowSorb 2300 is injected at room temperature and must thus multiplied by the ratios 273.2/ (Rm.Temp.,oK)x(Atm. Press., mmHg)/760 to convert it to standard conditions (oC and 760 mmHg). Avogardo’s number A is 6.023x1023 molecules/g mole. The molar volume M of a gas at standard conditions is 22.414 cm3/gmole. The presently accepted value for the area N of a solid surface occupied by an adsorbed nitrogen molecule (2) is 16.2x10-20 m2 (=16.2 Angstroms 2 ). P is 0.3x the atmospheric pressure in millimeters of mercury since the gas mixture is 30% nitrogen and adsorption takes place at atmospheric pressure. Pa, the saturation pressure of liquid nitrogen is typically a small amount greater than atmospheric due to thermally induced circulation, dissolved oxygen, and other factors. With fresh,

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relatively pure liquid nitrogen, the saturation pressure is typically about 15 mmHg greater than atmospheric pressure. It can be 40 to 50 mmHg greater if the liquid nitrogen is relatively impure. The saturation pressure should be determined by other means in the latter event. The result for a 30% N2 / 70 % He mixture adsorbed at liquid nitrogen temperature when room temperature is 22 oC and atmospheric pressure is 760 mmHg is the expression S = V [273.2/Rm.Temp.] [Atm. Press./760] [6.023x1023 x16.2x10-20 /22.414x103] [1((%N2/100)xAtm.Press.)] = V x 273.2/295.2 x 760/760 x [6.023x1023 x16.2x10-20]/22.414x103 x1-0.3x760/775 = 2.84 Where S: is the surface area in square meters. For Calibration purposes, this means that a syringe injection of V=1.00 cm3 of nitrogen at 22 oC and 760 mmHg should produce an indicated surface area of 2.84 m2. The value of S from equation 7 changes when ambient conditions differ significantly from 22 oC and 760 mmHg, pressure changes having relatively effect than temperature. For example, if the gas were 29.33 % N2, the ambient temperature was 25 oC, atmospheric pressure were 710 mm Hg, and the saturation pressure were measured to be 735 mm Hg, the value, instead of being 2.84, should be 2.67. The surface area of carbons and activated carbons was measured with FLOWSORB 2300 by determining the quantity of a gas that adsorbs as a single layer of molecules, a so called monomolecular layer, on a sample. This adsorption is done at or near the boiling point of the adsorbate gas. The area of the sample is directly calculable from the number of the adsorbed molecules, which is derived from the gas quantity at the prescribed conditions, and the area occupied by each. For a nitrogen and helium mixture of 30 vol. % nitrogen, conditions most favorable for the formation of a monolayer of absorbed nitrogen are established at atmospheric pressure and the temperature of liquid nitrogen. Surface area is computed from the data obtained when either the pore filling or emptying process is followed by exposing a porous material to progressively increasing or decreasing concentrations of nitrogen gas. Adsorption and desorption surfaces for each sample was measured and the specific surface was obtained by taking the average of both adsorption and desorption surfaces divided by the weight of the sample, weighed before the desorption and after. Estimation of a commercial active carbon NORIT B.E.T specific surface was also performed in order to compare surface values of tires issued activated carbons with the commercial ones.

Porosity In order to fully characterize the pore volume and size of carbons, a combination of methods can be used. The αs method is an empirical one, that compares sample isotherm with that of a reference non-porous carbon material possessing chemically similar surface. According to the αs plot characteristics; qualitative and quantitative information can be obtained about porous structure. At high pressures (αs >1) all αs plots present a linear part with some slop as a result of multiplayer adsorption in large dimension pores (mesopores).

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Total microporosity, Vtot,µ, is estimated from the intercept of this linear part as usual for the αs plots [55]. Surface coverage of the supermicropore walls is indicated by the appearance of a linear section at αs >0.5. Extrapolation of this section to αs =0 provides an approximate evaluation of the effective ultramicropore volume, Vuµ. Effective supermicropore volume can be regarded as the difference between Vtot,µ and Vuµ. Mesopores constitute a small percentage of the total porosity at low conversions (1-5 %) and increase slightly at high conversions to 10-15 %. In contrast samples posses in large part micropores as shown from the effective micropore volumes calculated from the αs plots. Micropore volume is distributed in larger dimension supermicropores at low conversions. At high conversions ultramicropores are created to some degree. The general trend is that as activation proceeds all kinds of porosity are increasing. At the final conditions of 900 oC and 4 h, an activated carbon is obtained possessing the entire spectrum of pore sizes, (super) micropores prevailing. Based on the trend of the experimental results, it can be anticipated that extension of the activation process will give a more mesoporous carbon with augmented percentage of ultra micro porosity [55] Dudinin-Radushkevich (DR) plots has been demonstrated to linearize type I isotherms over a wide range of relative pressures. Various types of deviations from linearity (and from type I isotherms) have been reported and were explained on the basis of porosity discrepancies from pure microporosity, [72]. Generally, long linear DR plots are given by carbons with narrow micropores, whereas the more restricted linearity is an indication of the presence of wider micro pores {super micropopres) and mesopores. From the DR plots the apparent micro pore volume can be estimated from the slop of the intercept of the linear part of the plot. Values of Vuµ and Vµ,DR should be in close agreement if the super micropores are absent.. Deviations are higher at higher degrees of burn-off and are attributed to the adsorption in wider pores with mechanisms such as filling of super micropores and multiplayer adsorption in the mesopores. It can be concluded that KOH activation produces at the early stages carbons with microporous structure. At late stages of activation carbons posses mixed micro- and mesoporous structure. During activation both pore ranges are evolving by generation of micropores and widening of the original narrow micropores.

KINETIC MODELLING Biomass pyrolysis is generally a complex process affected by biomass type, experimental system, temperature, pressure, residence time. The secondary reactions of the primary pyrolysis volatile products play an important role. At higher temperatures the secondary decomposition of liquids follows by high endothermic reactions. Shafizadeh [94] has studied the pyrolysis of wood by considering tree parallel reactions for the production of gas, liquids and char, as following: gas

k k

wood k

liquid char

k

H/C + CO + CO2

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−

where :

dW dt

= K ⋅ (W − W ∞

K = ko ⋅e

−E

)n

175

(1)

RT

W : Weight losses W∞ : Total weight losses (total decomposition) n : receiving ~1 K : Arrhenius kinetic constant ko : Pre-exponential factor of the reaction Ε : Activation Energy Anthony and Howard [56], Numm et al [95] have suggested another kinetic model for the estimation of the kinetic parameters koi, Ei, Vi f of biomass pyrolysis. This model is simple, useful in engineering calculations. In this model the rate of formation of a product is given by the expression:

(

dVi = K i ⋅ V ∞ − Vi dt

Where:

)

n

K i = k oi ⋅ e

− Ei

(2)

RT

Vi : Percentage of volatiles in time t V ∞ : Ultimate attainable yield Ki : Arrhenius kinetic constant koi : Pre-exponential factor Εi : Activation Energy The basic difference between the above models is that, the first assumes total decomposition of the raw material while the second considers an ultimate attainable yield of decomposition (ultimate yield of volatiles and gases). Many investigators in the past applied the single first order reaction model [83, 84], the two competing reaction model [85] or other more complicated model [86]. In the present work, the model of Anthony and Howard [56] was applied. It is based on the first order decomposition reaction model, but it assumed that the thermal decomposition of raw material consists of a large number of independent chemical reactions. Each of these reactions is described as irreversible first order in the amount of volatile yet to be released. In this model the rate of formation of a product is given by the expression:

(

dVi = K i ⋅ V ∞ − Vi dt

)

n

(1)

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K i = k oi ⋅ e

Where :

− Ei

RT

Vi : Percentage of volatile at time t V ∞ : Ultimate attainable yield Ki : Arrhenius kinetic constant koi : Pre-exponential factor Εi : Activation Energy Equation (1) can be integrated assuming a constant heating rate

dT = m , until final dt

temperature is reached:

  R ⋅ T2  − E   ⋅ exp Vi = V ∞ ⋅ 1 − exp −    R ⋅ T     E⋅m

(2)

Following the above model, kinetic parameters were obtained for cotton gin waste (E, Kio, V) using the Levenberg - Marquardt method of non-linear regression analysis.

EXPERIMENTAL Pyrolysis Pyrolysis of wastes was carried out in our laboratory reactor (Figure 2). The apparatus employed for the pyrolysis was a captive sample reactor, offering advantages such as: − − −

Independent control of parameters, such as final temperature, heating rate and residence time. Very effective heat transfer. Nearly zero residence time at the final temperature and rapid cooling of the gaseous products.

The experimental procedure is presented in Figure 3. The experiments were carried out in the temperature range 390 - 890 ºC, with heating rates of 70 - 90 ºC/sec at atmospheric pressure, under helium. The main procedure apparatus consisted of the following: − − − − − −

Reactor Electrical circuit Cooling of gaseous products Trap for moisture collection System for gas collection System of gas analyses (GC)

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Trap2 Pressure gauge

Trap1 Flange SS316 Connection Plexiglass

Flanges of bronze

electrode

Flange SS316 Support flange

Figure 2. Laboratory reactor.

The reactor is a cylindrical Plexiglass vessel, of an inner diameter of 7cm and is 12 cm high. The reactor vessel closes with two pairs of flanges (top and bottom). The upper pair of flanges is made of stainless steel SS316. Between the flanges, elastic o-ring is fitted, in order to achieve isolation. The stainless steel flange has a diameter of 12 cm and a thickness of 1cm. In the centre there a 0.3125 mm diameter hole serving for the gas exit, while on it are fitted a filter for tar collection and traps (T1, T2) for liquids collection. On the flange, a second similar hole serves for the fitting of a manometer, in order to measure the pressure in the reactor. About 200 mg of the waste material is spread in a layer on a screen of stainless steel, which is inserted between the electrodes. Helium is passed through the reactor at the rate of 30cm3/min. The sample temperature is raised at the peak temperature. The reaction effluent includes fine charcoal, gas and volatile compounds. Their quenching occurs by natural cooling. The charcoal remains on the screen and is determined gravimetrically. Tar is defined as the material condensed within the reactor vessel, on the wall, flanges and on a paper filter at the exit of the reactor, at room temperature. Tar condensed inside the reactor is removed by washing with CH2Cl2 soaked filter paper and is measured gravimetrically. Hydrocarbons (in the vapour phase at room temperature) are collected in two lipophilic traps placed at the exit of the reactor and containing 80/100 mesh Porapaq Q chromatographic packing and then measured gravimetrically.

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A. A. Zabaniotou Cooling coil Volumetric cylinder Π2

Silica Gel

H/C trap Π1

Tar E2

B1 Ε5

Β2 Ε6

Ε4

E3

Pessure gauge

Tar filter

Ε4: Gas entrance Ε5: To gas collection Ε6: To trap

ΤΒ

Β2: 3-way valve

Ε1

H2O trap

Tar Thermocouple

Electrods Temperature recorder ΤΒ: 3-way electrovalve

E1: Gas Entrance Ε2: Exit to enviroment Ε3: To gas trap H2O

Sample

He

Micrometric valve

High amperage circuit

Gas collection trap

Figure 3. Experimental procedure

Gaseous products pass through two traps (T1 and T2), where the liquid HC are collected. Then, they pass through a water-cooling coil to be cooled to ambient temperature and then through a moisture collection trap, which is a cylindrical plexiglass tube containing silica gel. Finally they reach the gas collection trap through the electro valve TB. The volume of the removed water determines the gas volume. The gaseous products are selected in plastic sacs and they follow gas chromatography analysis. Gaseous products were passed through two traps (T1 and T2), where the liquid HC were collected. Then, they were passed through a water-cooled coil and cooled to ambient temperature and then through a moisture collection trap (a Plexiglass cylindrical tube containing silica gel). Finally, they reached the gas collection trap through the electrovalve TB. The volume of the water displaced determined the gas volume. The gaseous products were collected in plastic bags and analyzed by gas chromatography. Gaseous products were analysed in a Perkin-Elmer model Sigma 300 gas chromatograph, with thermal conductivity detector connected to a PC. A cart type HP 35900D A/D and a HP 3365 Series II ChemStations softword did the integration of the exit signal. The elemental analysis of biomass was carried out using a LECO COR Analyzer CHN800. C, H, N was measured directly, but oxygen was determined by difference. Determination of ash and moisture was performed according to ASTM Standards (D-1102-84 for ash in wood and D-2016-74 for moisture).

Olive Kernels Olive wood and kernels from Greece, ware used for pyrolysis experiments. Samples were prepared by cutting and crushing pieces of the raw material to fractions of the desired particle size (18-80 U.S standard mesh). The temperature range studied was 350-850oC and the

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heating rate was 80-100oC. The pyrolysis yielded char, liquid HC and tar and gaseous products. Composition of olive wood and kernel is presented in Tables 10, 11. Cotton gin waste from Central Greece was used as raw material for the experiments. The chemical composition of cotton gin waste and of other agricultural and forestry residues, as reported in the literature, are presented in Table 9, where a comparison of the chemical characteristics of the various wastes [57,65,66,67] is made. It can be deduced from Table 9 that the total organic matter (C, H, O) of the cotton gin waste is about 80% wt./wt. and the heating value is 15.780 kJ/kg. This convertible part is rather close to organic waste materials, such as rice straw and rice husks. The ash content of the cotton gin is rather high (15wt.%) which is much higher than that of wood residues (Table 10). Cotton gin waste is very loose compared to other biomass materials. Its bulk density is about 25 kg/m3, which is smaller than of straw waste (40-50 kg/m3) [57], and particle size and shape are not uniform. The heat content of cotton gin waste was estimated, by the following equation [68]:

Q = 146.58 ⋅ C + 568.78 ⋅ H − 51.53 ⋅ O Where Q is the gross heat content (Btu/lb) and C, H and O are respectively the amount of carbon, hydrogen and oxygen in weight percent. Table 9. Elemental Analysis and Characteristics of different types of biomass (wt.%, dry basis) Material

Cotton gin waste Cotton gin waste Cotton straw

C

H

N

S

41.23

5.03

2.63

43.8245.97 45.5

4.624.85 6.01

2.952.04 0.98

Ash

Moisture

Heating Value (kJ/kg)

13.3

6.0

15780

11.8812.46 17.2

0.0

15480

0.0

18330

O

Assumed 34.0 to be 0.0 0.43-0.45 32.6134.23 0.23 30.08

Table 10. Elemental analysis of waste Raw material characteristics (maf : moisture and ash free)

C *(wt. % maf) H (wt.% maf) N (wt. % maf) O (wt.% maf) Ash (wt. % mf) Moisture (wt. %) Heating value (kcal/kg)

Olive wood

Olive kernel

Cotton gin

Used tires

45.6 6.19 0.00 40.11 1.06 15.45 4658

44.30 5.85 0.00 49.85 3.90 21.50 4916

41.23 5.03 2.63 34.0 13.3 6.0 3775

79.89 6.74

0.51 8210.5

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A. A. Zabaniotou Table 11. Analysis of olive kernel waste and char

Raw material (% w/w), dry basis 1.95 49.74 6.06 0.18 39.07 3.0

N C H S O Ash

Char (% w/w) dry basis 1.35 75.68 0.79 0.00 12.18 10.0

Used Tires Pyrolysis of used tires has been performed in two scales: a) at the captive sample reactor (described previously) and b) in a pilot scale at the Compact Power Ltd at Bristol, U.K. Compact Power Ltd has developed a new advanced thermal conversion technology for a wide range of wastes using the process of pyrolysis, gasification and high temperature oxidation. The plant is designed as a closed system in which all waste materials are converted into simple gases and used to fuel conventional steam power circles. The used tires were pyrolyzed without elimination of their included metallic part. The pyrolysis was carried at 800 °C during 45 min in an inert atmosphere, in the Avonmonth’s industrial pyrolyser, with a capacity of 1 t/h. Tires were heated in the absence of oxygen to about 800 °C. Hydrocarbons were converted to simple gases, leaving a residue of carbon CBp, inert materials and heavy metals. In a next step, 11 kg of tires pyrolysis CBp issued from Compact Power were used for the preparation of 5 kg sample for batch activation. First, the maximum of steel content was eliminated. By manual magnetically removing, 23 wt. % of CBp has been separated. Those were large particles and Fe containing particles. 5 kg of that CBp have been used for activation. Caracteristics and composition of used tires are given in Table 12. Table 12. Elemental analysis, moisture and heat content of tires and char

Raw Material Char

Elemental Analysis %wt C %wt H 79,87 6,74 86,58 3,33

Moisture %wt 0,51 1,65

Heat Content MJ/Kg 36,65 34,32

RESULTS Olive Wood (Cuttings) Pyrolysis A set of experiments of olive wood pyrolysis was performed at a temperature range of 275- 610oC. The heating rate ranged between 100-300oC/sec. The residence time in the maximum temperature, varied between 0.5-1.0 sec. Data on the effect of temperature on the yields of char, gases and tar from pyrolysis of dry olive cuttings are presented in Figure 5. Weight losses increase with temperature (Figure 5), until 91% conversion to volatile material attained at 610oC. Most of devolatilization occurs between 300oC and 600oC [67].

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PI VENT PI BM

TI

PI

WTGM CO

PI 2

VENT

TI

SP

SAMPLE

FM

PI

BAGS

PI N

2

SP PI

: Sample Port : Pressure Indicator

TI

: Temperature Indicator

BM

: Bubble Meter

FM

: Flow Meter

WTGM : Wet Test Gas Meter Figure 4. Activation reactor 100 C harcoal

Yields of pyrolysis products (wt.-% of dry olive wood)

Tar G ases

75

Liquids

50

25

0 200

300

400

500

600

700

Peak Tem perature (°C ) Figure 5. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry

The yield of charcoal decreases increasing the temperature. The charcoal yield reaches the value of 25 wt.%, at 550oC. Tar yield goes through a maximum of 35 wt. %, at about 550oC. Above this temperature, tar yields decrease due to secondary reactions producing more gaseous products. Tar and gaseous products are initially evolved at the same

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temperature (270oC). CO is observed at about 270oC and its yield increases with temperature to a value of 30 wt.% at 400 oC, remaining constant until 500oC and above 500oC increases rapidly reaching the double value (~ 60 wt.%) at 600oC. On a weight basis, CO dominates the gaseous products at the above temperatures. This is probably due to the fact that CO is also a product of secondary cracking of the tar [67].

Olive Kernel Pyrolysis A second set of experiments has been performed at a temperature range of 335-600oC, with samples of olive kernels. The heating rate ranged between 100-240oC/sec and the residence time varied between 0.1-0.5 sec in the maximum temperature. Data of the temperature effects on the yields of char, gases and tar from pyrolysis of dry olive kernels, are presented in Figure 6. 100

Charcoal

90

Tar 80

(wt.-% of dry olive kernal)

Yields of pyrolysis products

Gases 70

Liquids

60 50 40 30 20 10 0 300

400

500

600

Peak Temperature (°C) Figure 6. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry olive kernel

The yield of charcoal decreases to a value of 33 wt.% of dry sample, at 500oC. Above 500 C, this yield tends to be stabilized to a value of 30 (wt.%). Char was analyzed and the results of the elemental analysis, as well as the moisture and the heat content of carbon residue are shown on Table 10. Weight losses increase with temperature and a conversion ~70% to volatile material is attained at 580-600oC (Figure 6). Most of devolatilization occurs between 400oC and 550oC. Tar yield goes through a maximum of ~30 wt.% at about 450500oC. Above this temperature, tar yield decreases, due to secondary reactions producing more gaseous products. The rate of this increase is lower than the analogous observed at olive o

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wood pyrolysis. Tar and gaseous products are initially evolved at the same temperature (350oC), [1, 67].

Cotton Ginning Waste Pyrolysis The effect of temperature on total weight loss from cotton gin waste pyrolysis is shown in Figure 7. A dramatic increase in weight loss is observed with increase in temperature, which approaches an asymptotic value of 60 wt.% at approx. 600oC. Figure 5 depicts the product yield (char, liquid and gas) in relation to temperature. Pyrolysis of cotton gin waste apparently starts before reaching the temperature of 350oC. The yield of char decreased with temperature approaching the asymptotic value of 35-40 wt.%, at nearly 700°C (Figure 7), [89].

Pyrolysis Product Yields (% wt of m.a.f. cotton gin waste)

100 Char Gases Tar Liquid H/C

90 80 70 60 50 40 30 20 10 0 300

400

500

600

700

800

900

Peak Temeperature (o C) Figure 7. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry cotton gin

Pyrolysis of cotton gin wastes seems to give very low yields of tar and liquid H/C (almost negligible), probably due to the high cellulose content, as reported by other researcher [70]. This could be interpreted as reflecting competition between escape of freshly formed tar from elevated temperature environment and cracking of the tar in that environment. This may happen because at low heating rates, there is adequate time during the heat up period for most of the tar formed to escape the immediate neighborhood of the screen before the temperatures are sufficiently high for extensive cracking to occur [69]. This secondary cracking of tar is believed to be a significant pathway for production of H2, CO and several light HC such as CH4, C2H4 [69, 89]. The total amount of gases tends to sharply increase with temperature at low temperature levels. The rate of increase decreases at higher temperatures (600-800oC). Gas chromatographic analysis shows that the gaseous product consists of CO, H2, CH4 and small amounts of C2H4. The main gaseous product is CO [89]

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Used Tires Pyrolysis Figure 8 depicts the product yield (char, tar, liquid and gaseous products) in relation to the temperature of pyrolysis. Carbon black yield decreased with temperature reaching an asymptotic value of 20 wt. % of raw material, at about 830ºC. Gas yield increased with temperature reaching an asymptotic value of 73 wt. % of raw material, at about 830ºC. An increase in the amount of gases might have been expected and a consequent decrease in liquids, due to the stronger thermal cracking produced at higher temperatures. Tar and liquid hydrocarbon yields were small and increased slowly with temperature. With respect to gas pyrolysis products, gases have been analyzed by gas chromatography. As far as liquids are concerned, those were only measured and their contribution to the mass balance has only performed. No liquids characteristics were determined, since the purpose of the present study was the investigation of alternatives uses of char. 100 Yield of pyrolysis products (wt.%)

90 80 70 60 50 40 30 20 10 0 350

450

550

650

750

850

950

o

Temperature ( C)

Figure 8. Effect of temperature on the yields of char, gases and tar from pyrolysis of used tires

In contrary, char was analyzed and the results of the elemental analysis, as well as the moisture and the heat content of carbon residue are shown on Table 12. In the same table the analogous characteristics of tire as raw material, are presented. The C content of the carbon black is 86,58 wt. %, while that of coal is 71,6 [10] and the lower calorific value of the char was measured to be 34,32 Mj/kg, while that of coal is 29,0 Mj/kg [3, 36, 44].

Activation Physical and chemical activation has been used in this study. The more successful stories are presented following:

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Physical Activation of Char from Tires For tire char physical gasification has been applied in two scales: a) Tires char air gasification and activation tests have been conducted in the set-up shown in Figure 4. A tubular stainless steel reactor was used heated externally by an electric furnace. In our laboratory, various sizes of reactors were used, 1/2-2 ½’’ of nominal diameter alternatively, permitting experiments with varying sample weight. Quantities of 1 g to 1 kg of raw material can be fed to the reactor and heat treated up to 1000 oC. b) Tires steam/CO2 activation in a pilot unit at NESA Company.

Steam Activation of Char from Tires The activation of about 5 kg of char brut issued from tires, was activated in an activation kiln at NESA company, at Louvain la Neuve [90]. The steam activation of tires char has performed at 970 °C for 3 hours. Each half an hour during the activation process, a sample of activated carbon was taken cooled and inserted in a plastic bag for further characterisation [36]. The oxidizing agent tested in this study was H2O mixed with CO2 produced by the natural gas combustion in the combustion chamber of an industrial reactor used for the purpose, owned by NESA company in Belgium.; the hot combustion gases were ducted to the top of the reaction chamber in the NESA furnace where they came into contact with the tested material, simultaneously with the steam injection in the reaction chamber. The fact that the combustion gases were ducted came in contact with the char, resulted in steam/CO2 activation [36]. Chemical Activation of Olive Kernels Chemical activation with KOH has been performed for olive kernels char. Activation of the produced olive kernel char, [55], was conducted in the same apparatus of pyrolysis for chemical activation. The char was mixed with KOH, in a ratio C/KOH of 1:4 suggested in literature to be the optimum [71]. Activated carbons with various extents of burn-off were prepared by varying the activation temperature to 800 and 900 oC and time to 1, 2, 3 or 4 hrs. Carbonized products were cooled and washed by boiling with HCl for 1h for residual KOH removal. The acid washed samples were further washed with distilled water several times until neutral pH. The final carbon products were dried at 110oC for 24 hrs, for moisture removal [55].

Characteristics of Activated Carbons Activation carbons were analyzed afterwards in the Laboratory. N2 adsorption at –196oC and desorption at 250oC was utilized to determine specific surface areas of the activated carbons samples by an automated adsorption/ desorption apparatus (Micromeritics, ASAP). In this study the best produced activated carbons are those obtained from olive kernels with KOH activation and from tires obtained with steam activation and they are described as in following:

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Olive Kernels Best Activated Carbons The most important property of the activated carbon is its adsorptive capacity, which in general is proportional to the surface area. Although the BET equation is the most widely used for evaluating the surface area, there is a degree of uncertainty in determining the range of relative pressure over which can be applied. The problem is even more complicate when micro porosity is present. In such cases the range of applicability is narrower and as recommended in literature lies between P/Po=0.01-0.2, [72]. For activated carbons, the pore volume is another parameter that characterizes their pore structure. Total pore volumes are generally increased with time and temperature varying between 0.57and 1.52 cm3/g, Table 13, and follow a similar trend with surface areas i. e. they are increasing monotonically with burn-off. Table 13. Structural parameters of olive kernel carbons T, oC 800 800 800 800 900 900 900 900 F300

T, h 1 2 3 4 1 2 3 4 -

X 24 28 51 58 35 41 53 68 -

1-X 76 72 49 42 65 59 47 32 -

SBET 1339 1334 2578 2431 1550 1462 1798 3049 960

Vtot. 0.595 0.580 1.062 1.033 0.679 0.665 0.842 1.52 0.56

Vtot. µ 0.594 0.573 0.991 0.983 0.665 0.637 0.750 1.300 0.46

Vm 0.001 0.007 0.071 0.050 0.014 0.028 0.092 0.220 0.10

Vuµ 0.000 0.000 0.000 0.000 0.071 0.085 0.100 0.113 -

Vsµ 0.355 0.389 0.991 0.983 0.594 0.552 0.650 1.187 -

VµDR 0.482 0.459 0.768 0.705 0.458 0.400 0.627 0.790 -

In the production of commercial activated carbons, relatively high product yields are expected. Carbon yields are calculated by the difference between 100 and conversion. The yields of activated carbons produced from olive kernels range between 76 to 32 % by weight depending on activation time and temperature. Those values are satisfactory in virtue of a possible commercial use. Olive kernel active carbons produced by chemical activation, show the highest BET surface areas. These are increasing with activation time and temperature from a minimum value of 1339 at 1 h and 800o C to a maximum of 3049 m2/g at 4 h and 900o C. On the other hand, BET area shows an increase with an increase of the burn-off, regardless of the activation temperature. This indicates that the burn-off of the activated carbon has the most significant effect on the increase of the surface area. Indeed, the surface area depends on the mass, removed during the activation of the carbon, creating pores to the material. The range of linearity in the BET plots was found to be satisfactory within this range of values for the carbons prepared from olive seed residues [55]. For activated carbons, the pore volume is another parameter that characterizes their pore structure. Total pore volumes of olive kernel carbons are generally increased with time and temperature varying between 0.57and 1.52 cm3/g, and follow a similar trend with surface areas i. e. they are increasing monotonically with burn-off [55].

Used Tires Best Active Carbons Proximate analysis of produced active carbons is presented in Table 12. Active carbon is a carbonaceous material with a highly developed internal surface area and with strong

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adsorptive capacity. Theoretically, any carbonaceous material can be converted into active carbon by an appropriate physical activation process. A pore system is developed using oxidizing agents such as carbon dioxide, air or steam, heated to 700-100oC. The surface area was found to increase upon activation to reach a maximum at a burn-off level of 70 %. This was followed by decrease with further activation. The best activation time was 2.30 hr at 1000oC. After 2 hr of activation time, the best-activated material was produced yielding a medium level of microporocity. Higher times yielded high burn-off levels and a reduction in the surface area, microporocity and adsorption of N2. This is consistent with the previous work by C.I Saint –Diaz, A.J. Griffiths [73], where it seems that the initial stages of the activation process, the peripheral and more accessible single aromatic sheets can be burned off, producing mainly micropores. The availability of those sheets is decreasing and larger sheets start burning out converting more and more of the micropores into macropores decreasing therefore the surface area at higher activation time [73]. The best B.E.T surface area with a value of 431,2 m2/g were obtained at 2 ½ h of steam activation in pilot scale. The activated carbon produced after 3 hours of activation showed lower values of B.E.T surface area due to the destruction of pores. The surface area might be improved with other methods of activation. The acid treatment e.g prior to steam activation, such as with HNO3, performed by P. Ariyadejwanich et al [74], showed that highly mesoporous activated carbons could be obtained with a B.E.T surface area of 1119 m2/g. The surface area of activated tire carbons is not much lower than those reported in the literature. Helleur et al [75] produced activated carbon with surface not greater than 320m2/g. Their explanation to that was that reasons for the low surface area might be the activation conditions and the high ash content of the tire which is the case of this study also. Saint-Diaz et al [73] have reported medium surface area, 431m2/g from tire derived char at 1000oC. The above researchers in their study had mentioned that given that pyrolysis process generates large quantities of CO2 and heat (pilot-scale flaming pyrolyser), it is probable that either the CO2 method or steam activation would be used in an industrial scale. In the present study the activation has performed under CO2/steam and the results are better, reinforcing the conclusion of using the method at industrial scale. Both carbon dioxide and steam are mild oxidant and eliminate carbon atoms from the char particle [76]. F. Rodriguez-Reinoso et al [76] have studied the use of steam and CO2 as activated agents in the preparation of activated carbons and they invistigated that carbon dioxide produces an opening, followed later by widening, of narrow microporosity, whereas steam widens the microporosity, from the early stages of the activation process. The results of the present study are in agreement with this statement. A. Zabaniotou et al [36, 44] in a series of experiments investigating the operating conditions giving the maximum sample surface area, have measured B.E.T surface areas around 600m2/g for both CO2 and steam activation. However, the above mentioned study has performed in a laboratory scale reactor, using omogenous fine tire char particle of 200 µm. Ariyadejwanich et al [74] obtained activated carbons by activation of char with steam at 850oC with B.E.T surface areas up to 737m2/g, while San Miguel et al [77] obtained 1070 m2/g B.E.T surface areas. The B.E.T surface area of the pyrolysis tire chars found to be about 600m2/g, which is almost typical value for chars prepared from waste tires [74].

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Comparisons with the Commercial Active Carbons For the comparison of active carbons produced from olive kernel with chemical activation and commercial ones, the commercial grade carbons such as, Calgon Filtrasorb 300 (F300, Calgon Carbon Co., Pittsburgh, USA), have been used, their characteristics provided in Table 14. The BET surface areas and the pore volume of the produced activated carbons are much higher than that of the commercial carbon. Its pore size distribution is similar to carbons with high burn-off possessing large percentage of micropores. Olive seed super activated carbons present adsorption and porosity characteristics quite similar to those prepared from other raw materials by KOH activation. For example, Maxsorb, which is a commercial product prepared from petroleum coke, posses a BET surface area value of 3100 m2/g, very close to sample of 900o C-4 h. AMOCO carbon PX-21 and Anderson AX-21 present slightly higher areas and pore volumes, table 3, probably due to different activation conditions and starting materials [55]. Table 14. Surface areas and pore volumes of some super activated carbons Sample

AX21 PX21 Maxsorb

BET area (mg/m3) 3390 3700 3100

Total micropore volume 1.52 1.75 -

Ultra micropore volume 0.36 0.39 -

Super micropore volume 1.16 1.36 -

These enormous BET surface areas are created by a distinct KOH activation mechanism. Investigations [59, 78, 79, 80, 81] showed that KOH is dehydrated to K2O, which reacts with CO2 produced by the water-shift reaction, to give K2CO3. Intercalation of metallic potassium, which also formed above 700o C, appeared to be responsible for the drastic expansion of the carbon material and hence the creation of a large specific surface area and high pore volume. Olive seed super activated carbons present adsorption and porosity characteristics quite similar to those prepared from other raw materials by KOH activation. For example, Maxsorb, which is a commercial product prepared from petroleum coke, posses a BET surface area value of 3100 m2/g, very close to sample of 900o C-4 h. AMOCO carbon PX-21 and Anderson AX-21 present slightly higher areas and pore volumes, Table 14, probably due to different activation conditions and starting materials [55]. For the comparison of active carbons produced from tires with physical activation and commercial ones, the commercial activated carbon NORIT GL 50 is used. NORIT GL 50 is a powdered steam activated carbon with an extra fine particle size that can be used in a large range of applications. This carbon is especially suitable for the removal of dioxins, mercury and other contaminant traces from flue gases. Its fine particle contributes to its good adsorbion kinetics. Table 15 presents its specifications and general characteristics. All analyses based on NORIT Standard Test Methods (NSTM). General characteristics reflect average values of product quality. Specifications are guaranteed values based on lot to lot quality control, as covered by NORIT ’s ISO 9002 certification [36, 88].

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Table 15. NORIT GL 50 specifications and general characteristics. Molasses number (EUR) Apparent density (tamped) Particle size Iodine number Moisture (as packed) Critical Ignition Temperature

500 490 kg/m3 20 µm 700 2 mass-% 260 oC

Kinetic Modeling The kinetic modelling resulted to kinetics parameters for total weight loss of olive kernel, olive wood, cooton gin waste pyrolysis. These parameters are given in Table 16. Comparison is also made with kinetic parameters for cellulose pyrolysis. Table 16. Kinetic parameters of pyrolysis for total weight loss of various agro-residues Type of Biomass Total Weight Losses Olive wood Olive kernel Cotton gin waste Cellulose

Experimental system

Temperature logko E V Reference (oC) (sec-1) (kcal gmol-1) (wt.%)

Captive sample reactor Captive sample reactor Captive sample reactor Captive sample reactor

300-600 250-400 350-800 300-1100

0.92 4.6 3.25 8.3

2.624 11.142 11.424 31.79

91.00 67.60 65.26 94.08

[67] [67] [89] [71]

CONCLUSION The main conclusions of the study are: −

−

Activated carbon surfaces have a pore size that determine its adsorption capacity, a chemical structure that influences its interaction with polar and nonpolar adsorbates, and active sites which determine the type of chemical reactions with other molecules. Conversion of plentiful by-products into activated carbons that can be used in applications such as drinking water purification, waste treatments, treatment of dyes and metal-ions from aqueous solution would add value to agricultural commodities, help the agricultural economy with an additional market potential, offer solution to environmental problems and help reduce the cost of waste disposal. As the raw materials obtained from agricultural wastes are available freely and abundantly. Activated carbon from olive-kernel waste residues with chemical activation, using KOH as the activating agent, show higher adsorption capacities and higher surface areas than the commercial type. BET surface areas of carbons are increasing with activation time and temperature from a minimum value of 1339 at 1 h and 800o C to a maximum of 3049 m2/g at 4 h and 900o C. The absence of sulphur and the low ash content of the char are positive factors and make olive kernels a good precursor for the production of active carbons. Moreover, in comparison with the commercial

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−

carbon, which is mainly microporous, the produced carbons show a micropore distribution at low burn-offs, while at higher burn-offs an increase of the mesopore fraction was noticed. Used tire activated carbons posses surface areas around 600m2/g prepared by chemical activation with KOH, and 432m2/g prepared with CO2/ steam activation The use of catalyst can improve the surface areas making active carbons from tires acceptable substitutes of commercial products. From the experimental results, it can be concluded that a combination of a rotary kiln which presents good conditions for char preparation (low heating rate etc) with KOH activation could be a promising process in pyrolytic recycling of agricultural resisues for active carbon production

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Zabaniotou A.A. Value-added products (active carbon) from olive kernels pyrolytic char study in laboratory and bench/ilot scales. Submitted in Journal of Analytical Applied Pyrolysis. Savova D.; Apak E.; Ekinci E.; Yardim F.; Petrova N.; Budinova T.; Razvigorova M. and Minkova V. Biomass conversion to carbon adsorbents and gas. Biomass Bioenergy 21 (2001) 133-142. Zabaniotou A.A. and Karabelas A.J. Pyrolysis as a method for utilization of solid wastes in Greece (agricultural wastes and used tires). October 2002 Lanzetta M. and Blasi C.D. Pyrolysis kinetics of wheat and corn straw. J Anal Appl Pyrolysis 44 (1998) 181-192. Minkova V.; Razvigorova M.; Bjornbom E.; Zanzi R.; Budinova T. and Petrov N. Effect of water vapour and biomass nature on the yield and quality of the pyrolysis products from biomass. Fuel Proc Technology 70 (2001) 53-61. Haykiri-Acma H.; Yaman S. and Kucukbayrak S. Gasification of biomass chars in steam–nitrogen mixture. Energy Conversion Management (2005). Cetin E.; Moghtaderi B.; Gupta R. and Wall T.F. Influence of pyrolysis conditions on the structure and gasification reactivity of biomass chars. Fuel 83 (2004) 2139-2150. Fan M.; Marshall W.; Daugaard D. and Brown R.C. Steam activation of chars produced from oat hulls and corn stover. Bioresource Technology 93 (2004) 103-107. Tsai W. T.; Chang C.Y. and Lee S.L. Preparation and characterization of activated carbons from corn cob. (1997) 1198-1200. Putun A.E.; Ozbay N.; Onal E.P. and Putun E. Fixed-bed pyrolysis of cotton stalk for liquid and solid products. Fuel Processing Technology 86 (2005) 1207– 1219. Jensen P.A.; Sander B. and Johansen K.D. Pretreatment of straw for power production by pyrolysis and char wash. Biomass and Bioenergy 20 (2001) 431–446. Predel M. and Kaminsky W. Pyrolysis of rape-seed in a fluidized-bed reactor. Bioresource Technology 66 (1998) 113-117. Zhang T.; Walawender W.P.; Fan L.T.; Fan M.; Daugaard D. and Brown R.C. Preparation of activated carbon from forest and agricultural residues through CO2 activation. Chemical Engineering Journal 105 (2004) 53–59.

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Lillo-Rodenas M. A.; Cazorla-Amoros D., and Linares-Solano A. Understanding chemical reactions between carbons and NaOH and KOH: An insight into the chemical activation mechanism. Carbon, vol. 41 (2003) 267-275. Zabaniotou A.A.; Lappas A.A; Kousisdis N. Flash pyrolysis of Greek lignite. Journal of Analytical and Applied Pyrolyis, vol.21 (3) (1991) 293-304. Badzioch S. and Hawksley, P.G. Kinetics of thermal decomposition of pulverized coal particles. Ind. Eng. Proc. Dev., 1970, 9, 521-530. Nsakal N.Y.; Essenhigh R.H. and Walker P.L., Combustion Science and Technology 1977, 16, 153. Kobayashi H.P; Howard J.B. and Sarofim A.F., 16th Symposium on Combustion, The Combustion Institute, Pittsburg 1977, 411 Sitnai O. National Conference, Institute of Energy, 1976, Volume 76 http://www.illinois.com http://www.norit.com Zabaniotou A.A.; Roussos A.I. and Koroneos C.J. A laboratory study of cotton gin waste pyrolysis. J.A.A.P. vol.56 (1) (2000) p.47-59. http://www.nesa.solution.be http://www.etra-eu.com Agblevor F.A.; Cundiff J.S.; Mingle C. and Li W. Storage and characterization of cotton gin waste for ethanol production. Resources, Conservation and recycling 46 (2006) 198-216. Bacaoui A.; Yaacoubi A.; Dahbi A.; Bennouna C.; Phan Tan Luu R.; MaldonadoHodar F.J.; Rivera-Utrilla J. and Moreno-Castilla C. Optimization of conditions for the preparation of activated carbons from olive-waste cakes. Carbon 39 (2001) 425–432. Shafizadeh F. Fast pyrolysis of biomass.Proc. Specialists workshop, Solar Energy Research Institute, Colorado, Usa (1980). Nunn, R.; Howard, J.B.; Longwell, J.P.; Peters, W.A. Studies of the rapid pyrolysis of sweet gum hardwood. Fundamentals of Thermochemical Conversion, R.P.Overent, T.A. Milne, L.K. Mudge, Elsevier Applied Science, London, 293-313 (1985).

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 197-220 © 2006 Nova Science Publishers, Inc.

Chapter 6

ENERGY RECOVERY FROM WASTE INCINERATION: LINKING THE SYSTEMS OF ENERGY AND WASTE MANAGEMENT Kristina Holmgren∗ Linköping Institute of Technology, Linköping, Sweden

ABSTRACT Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. Waste incineration thereby links the systems of waste management and energy. This chapter addresses the importance of taking this into consideration when e.g. making investment decisions or designing policy instruments. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed, together with trading in waste and electricity and how this impacts waste incineration in Sweden. Conflicts between the internal market in the European Union and waste management goals are shown. When making investment decisions, various models are often used as decision support tools. Some models for assessing waste incineration/management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration.

∗

Corresponding author. Tel.: +46 13 286687; fax: +46 13 281788. E-mail address: [email protected]

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INTRODUCTION Energy recovery through waste incineration1 connects two vital systems in modern society: the waste management system and the energy system. In Sweden, with an extensive district heating (DH) system that supplies just over 40% of the total heating demand of buildings and premises, heat supply from waste incineration has a substantial share of the total DH supply of about 12% (Swedish Energy Agency, 2004). Furthermore, both these systems are the focus of attention due to environmental concerns, and for this reason, changes are being made in both systems. The European Union has common legislation which impacts both systems in the member countries. Apart from the legislation, the countries of the European Union are connected through trade; important in this case are the common electricity market and trading in waste. The aim of this chapter is to highlight two issues. The first is the dual purpose of waste incineration as a waste treatment method and as a supplier of electricity and/or heat. This chapter will emphasise the importance of taking this into consideration with regard to, e.g. decision making and when designing policy instruments. Two policy instruments that impact both technical systems will be described and the difficulties in handling the double function of waste incineration will be the central issue. These policy instruments are a recently proposed tax on incinerated waste in Sweden and green electricity certificates. Various models are often used as decision support tools in decision making processes, e.g. when municipalities make investment decisions. When designing and using these models, the dilemma of the two functions needs to be faced and the ways in which some models handle this will be described. Policy instruments in Sweden are highly dependant on legislation in the European Union, the policy instruments that will be described in this chapter are no exception. Therefore, the second issue in focus in this chapter is the connection via common legislation between countries in the EU. The consequences of this will be discussed, with a special emphasis on its impact on waste incineration in Sweden. Furthermore, the countries in the EU are connected via trade, and of special importance for waste incineration in Sweden is naturally the trade in waste, but also in electricity. The methodology applied to address these issues consists of a literature review and knowledge gained in earlier studies.

DEVELOPMENT OF WASTE INCINERATION IN SWEDEN This section will include a description of the historical development of waste incineration in Sweden. This information has been collected from a report from the Swedish Association of Waste Management (2005a) and from Hrelja (2006). The current situation with regard to waste incineration in Sweden will also be described, together with its impact on district heating, combined heat and power production and also the material recovery market. 1

Digestion also has this function, since it is a treatment method for easily biodegradable waste, where the residual products are a fertilizer and a gas which can be used for electricity and heat production or for transportation after cleaning, but this chapter will address only waste incineration.

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Historical Development Burning waste has been carried on for a long time; it has been done in the open at landfills or in simple furnaces in order to reduce waste volumes and decrease problems with vermin. This brought inconveniences, such as hazardous emissions to the atmosphere, and in 1903 Sweden’s first waste incineration plant began operations in Stockholm. However, it was not until the 1960s that waste incineration really began to show some development. The prerequisites for this were the district heating networks that began to appear after the Second World War, when municipalities’ interest in district heating was aroused. In 1948, Sweden’s first district heating network was operational in the city of Karlstad and other cities soon followed. This expansion created opportunities for waste incineration plants, since it provided an outlet for the heat produced, giving the waste a value. In the 1970s, waste began to be seen as a resource rather than a problem; in 1975 a proposition from the government stated that recovery had to increase in the future. The proposition did not state which technology was to be preferred, but incineration was regarded as preferable in bigger cities. As a result of the new view of waste as a resource, a number of plants with central sorting and composting were built. This venture failed since the plants did not work satisfactorily and there was no outlet for the residual product. This served to increase interest in waste incineration. Waste incineration expanded significantly, especially during the 1970s, over the years up until 1985. The number of plants increased from 2 in 1960 to 27 in 1985, and treatment capacity from 100,000 tons annually to 1,800,000 tons. The oil crises of the 1970s led to a growth in interest in waste incineration as an indigenous fuel, in order to decrease oil dependency.2 During the 1980s, researchers began to report widespread diffusion of heavy metals and dioxins in the environment and the effects on humans and animals. Waste incineration was found to be an important cause of this diffusion of hazardous substances in the environment.3 In 1985, a ban on investment in waste incineration was issued by the Swedish Environmental Agency, until the issues of emissions and technology had been solved. The Environmental Agency and the Energy Agency were commissioned to analyse the risks associated with waste incineration and concluded that it was possible to reduce the emissions to acceptable levels through a number of measures, including “cleaner” waste (i.e. more sorting of waste), more efficient combustion, advanced flue gas cleaning equipment, and the safe disposal of residual products. Limits were set for emissions. On the basis of these results, the ban on investment was lifted. Of the existing plants, 20 went through with modernisations while 7 were shut down. However, the debate on dioxins in the municipalities did not end there. Hrelja (2006) shows that in the 1980s the municipality of Skövde chose not to build a waste incineration plant due to lack of confidence in the treatment method. Later, however, Skövde went ahead and built the plant, which was inaugurated in 2005.

2 3

This was only one of a number of measures to decrease oil dependency. There are a number of sources, of which waste incineration is one. Industrial processes can also give raise to dioxins as can power plants using other fuels. Spontaneous fires at landfills are also a source of dioxins, where the contribution of emissions is hard to estimate.

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Waste Incineration in Sweden Today Today, there are 29 waste incineration facilities in Sweden, both hot water boilers (14) and combined heat and power plants (15) producing about 8.6 TWh heat and 0.74 TWh electricity (Swedish Association of Waste Management, 2005b). These facilities treat about 1.95 million tons of municipal waste and 1.2 million tons of other waste, mainly from the manufacturing industry. Cleaner fractions of waste can also be incinerated at other facilities and is not included in the figures presented here. Figure 1 shows the waste treatment methods for municipal waste in Sweden. As can be seen, energy recovery is the treatment method for almost half of the municipal waste today. This development is mainly a result of recent regulations in the waste management system aimed at decreasing landfill; the introduction of a tax on landfill in 2000, at present 46.3 €4/ton (Ministry of Finance, 2005a) and a ban on landfill of combustible waste from 2002 and from 2005 also of organic waste (Ministry of the Environment, 2001).

9%

1% 33%

47%

10%

Material recovery Biological treatment Energy recovery Landfill Hazardous waste

Figure 1. Treatment methods of municipal waste in 2004, total amount 4.2 million tons (Swedish Association of Waste Management, 2005b).

Capacity for waste incineration is currently increasing and is forecast to increase from 2.8 Mton in 2002 to 4.9 Mton in 2008, if all planned projects are carried out (Swedish Association of Waste Management, 2004), resulting in a total of 40 waste incineration plants. Despite these investments there will still be a lack of treatment capacity. The fact is that quantities of waste are also increasing, between 1985 and the present by some 2-3% per year. If this trend is not broken, additional waste treatment capacity will also be needed after 2008.

Waste Incineration and District Heating The role of waste as a fuel makes it part of the energy system. Therefore, the use of waste as a fuel is dependent on such factors as the prices of other fuels used, legislation, and policy instruments in the energy system. The value of using the waste is higher when the prices of e.g. fossil fuels or biofuel increase. Energy taxation in Sweden has had a significant effect on 4

An exchange rate is 1 € = 9.40 SEK is used throughout this chapter (January 2006).

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what fuels are used in the DH systems, since heat from fossil fuels has been heavily taxed.5 There has been a major shift from an almost total dependency on oil up until 1980 to a diversified supply where renewables represent a substantial proportion. This can be seen in Figure 2. A historical survey of the development of the DH sector can be found in Sjödin (2002).

60 Waste heat 50 40 30 20 10

Heat pumps Electric boilers Biofuel & peat Refuse Coal Natural gas Oil

19 70 19 73 19 76 19 79 19 82 19 85 19 88 19 91 19 94 19 97 20 00 20 03

0

Figure 2. Development of heat supply to the district heating networks between 1970 and 2003 (Swedish Energy Agency, 2004).

Palm (2004) shows that also institutional factors can connect the waste management system and the DH system. In the city of Linköping, one reason for the introduction of waste incineration was that the same municipal utility operated both the waste management system and the DH system and saw that with waste incineration they could solve two problems at the same time: both an acceptable waste treatment method and heat production for the DH system. A study by Sahlin et al (2004), which is an overview of the consequences of using waste as fuel in Swedish DH systems, also shows that waste incineration enables DH networks to expand due to the low cost of the heat.

Waste Incineration and Combined Heat and Power Production One disadvantage of waste incineration is the low electrical efficiency in the plants.6 This is due to the many impurities in the fuel; the temperature of the steam in the boiler can not exceed 400ºC without entailing high maintenance costs due to corrosion, as stated e.g. by Korobitsyn et al (1999). Combined heat and power (CHP) production is an efficient way to use resources and is recognized by the European Union as one of the measures needed to meet the demands in the Kyoto protocol (European Union, 2004a). Many utilities have 5

6

The carbon dioxide tax is at present 0.1 €/ton. More details of the energy taxation can be found e.g. in (Holmgren, 2006). The electrical efficiency of waste incineration plants is around 23% at capacity 30 MWe (Elforsk, 2003). By way of comparison, a natural gas fired CHP plant has an electrical efficiency of 46-49.5% at capacity 150 MWe and biomass fuelled power plants 34% at capacity 80 MWe (Elforsk, 2003).

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chosen not to invest in electricity production in their waste incineration plants due to difficulties in producing electricity in combination with historically low electricity prices in Sweden.7 However, electricity production at waste incineration plants is forecast to increase, from 0.7 to 1.7 TWh between 2002 and 2010. (Swedish District Heating Association, 2005). Existing waste-fired CHP plants will increase their electricity production and the total number of waste-fired CHP plants will double over the same period. The reason for the increase in electricity production at waste fired CHP plants is not clarified, but it is reasonable to believe that it is a result of the higher electricity prices anticipated when Swedish electricity prices are harmonized with those in continental Europe; this is further explained in the section on Impact on Waste Incineration of Trade in Electricity. The proposed tax on incinerated waste, which is designed to promote CHP production, is probably also a factor. In the municipalities that have a waste incineration plant, the plant is the base supplier of heat to the DH network, due to the negative operational cost of receiving the waste. This can remove the heat sink for more efficient plants and shorten their annual operational times. How to use the heat sink can in this perspective be seen as a conflict between waste management and the energy system. If waste incineration is chosen as the treatment method, it is vital to recover as much as possible of the energy content of the waste. This heat can occupy much of the heat sink leading to lower electricity production in the DH system, compared to if a plant with higher electrical efficiency were chosen instead of a waste incineration plant. Earlier studies have shown that this can be the case, e.g. for a municipal system (Holmgren and Bartlett, 2004) and an overall study of the DH systems in Sweden (Sahlin et al, 2004). This can of course vary between systems as shown by Holmgren (2006). This study deals with the ”competition” in the DH system in the city of Göteborg, where there is heat from waste incineration, waste heat from industries, and also investment in a natural gas fired CHP plant. There is room in the system for all types of waste heat; the new CHP plant mostly replaces heat boilers in the system.

Waste and Connection to the Material Market Waste management is connected to the material markets through the material recovery systems. However, the development of the material recovery system is highly dependent on political decision, such as the introduction of the concept of Producer Responsibility. The incentive to material recovery of municipal waste comes mainly from the Ordinance on Producer Responsibility, which includes packaging, cars, car tyres, newspapers, and electric and electronic devices (e.g. Ministry of the Environment, 1994; 1997). For the included fractions, levels of material recycling are stated. Packaging producers have set up companies to handle the collection of packaging. The companies have a deficit in financing this system, which the producers pay. This is different to newspapers, for example, which do not show this deficit in collection; a functioning market existed even before the legislation was introduced. Also, in industry, different metal fractions such as copper and steel have had a functioning market for recycling for a long time – half of the raw material used to produce steel comes

7

A more detailed explanation of this can be found e.g. in Trygg and Karlsson (2005).

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from collected scrap.8 The prices of materials naturally influence the attractiveness of material recovery.

CONNECTION BETWEEN COUNTRIES IN THE EUROPEAN UNION VIA LEGISLATION AND TRADE AND THE IMPACT ON THE SWEDISH WASTE INCINCERATION This section will describe the connections between EU countries in terms of common legislation and trade in waste and electricity. Differences and similarities in waste management and district heating will also be outlined.

European Legislation Affecting energy and Waste The common legislation in the European Union connects the countries to each other. This section will describe policies and directives that influence waste incineration. The European Union’s member states are obliged to implement the directives in their national legislation. The core of the European Union is the internal market which means free mobility of goods, services, people, and capital. This can be in conflict with waste management goals; examples are the principles of proximity and self-sufficiency, meaning that waste should be treated in the proximity of its origin and that member states should be self-reliant as regards treatment capacity. This is stated in the Framework Directive (European Union, 1975) which also defines waste as “any substance or object which the holder disposes of or is required to dispose of” and establishes the fundamental concept of the Polluter Pays Principle. One problem with the Framework Directive is that it does not clearly state when waste ceases to be waste and becomes a secondary material. In the Shipment of Waste Ordinance (European Council, 1993), waste is divided into two categories - for disposal and for recovery - where trading in the former is forbidden, in order to satisfy both the internal market and the proximity and self-sufficiency goals. Environmental concerns may be in conflict with free trade, both in terms of differing cost for waste treatment options due to varying standards and subsidies to the material recovery market. It is important to harmonise standards for waste treatment options in order not to “draw” waste to less controlled plants. The Directive on landfill (European Union, 1999) and the Directive on the incineration of waste (European Union, 2000) have this purpose. The Directive on the incineration of waste sets permitted maximum levels for emissions to the atmosphere and directions for monitoring the emissions. Emissions to water are also regulated, there are directions as to how the combustion process should be controlled, and how to take care of the residual products. It concerns both waste incineration plants and plants that burn both waste and other fuels, and has meant investment costs for the plants in Sweden in order to fulfil these demands. Whereas the directive is specific about emission levels, it is vague on how to classify efficient energy recovery of waste, which is a shortcoming. It says “the heat generated during the incineration and co8

Personal communication with Åsa Ekdahl, European Confederation of Iron and Steel Industries, 2003.

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incineration process is recovered as far as practicable e.g. through combined heat and power, the generating of process steam or district heating”. The performance of waste incineration plants differs widely, as can be seen from Figure 3, and is detailed further in the section on European differences in waste management and use of district heating. A definition of what an efficient energy recovery of waste is should be introduced. This weak point has been observed by the European Commission, which suggests that the energy efficiency of the plant should decide whether to classify it as a disposal plant or a recovery plant. The use of resources in other plants that the waste incineration plant could replace should also be taken into consideration (European Commission, 2005). The Landfill Directive specifies operational and technical requirements for landfills. It sets the demands that the pricing for receiving waste should include after-care for at least 30 years. It also dictates lower quantities of biodegradable waste in landfill and the collection of methane emissions. Apart from this, there is a directive on producer responsibility for packaging waste (European Union, 2004b), stipulating levels of material and/or energy recovery for different packaging materials. The EU’s waste policy is founded on the waste hierarchy, described in the Sixth Environmental Action Programme from the European Commission (2001) and states that first comes waste prevention, then recovery (reuse, material and energy recovery where material recovery, including biological treatment9 is preferred to energy recovery) and finally disposal, where landfill and waste incineration without energy recovery are included. Swedish waste policy is based upon this hierarchy. This does not go undisputed, however; in particular the question of whether energy recovery or material recovery, including biological treatment, is to be preferred, raises issues. Directives that impact the energy sector include the directive on the common electricity markets (European Union, 2003a), which states that Europe should have free trade in electricity in member states. This will mean higher electricity prices than historically in Sweden, since Sweden will be harmonized with continental Europe which currently has a higher electricity price (e.g. Trygg and Karlsson, 2005). This will further be described in the section on Impact on Waste Incineration of Trade in Electricity. There is a directive promoting CHP (European Union, 2004a), stating that CHP is an effective way to use resources and one measure to meet the demands in the Kyoto protocol. This has probably had an impact on the design of the proposed tax on incinerated waste, which will be explained in the section on Introduction of a tax on incinerated waste in Sweden. Recently, the European Union managed to agree on minimum energy tax levels (European Union, 2003b). There is a directive promoting electricity produced from renewable energy sources (European Union, 2001). Also this is seen as a measure to meet the demands in the Kyoto protocol and strengthening the domestic supply of energy. This has in Sweden led to the implementation of a system of green electricity certificates, which will be explained in the section on Green electricity certificates and waste incineration. Another directive regulates the emission allowance trading (European Union, 2003c). Waste incineration plants are not included in the trading sector, but are affected by the fact that the costs for fossil fuels increase as do

9

Biological treatment includes digestion and composting. When digested, biodegradable waste is degraded without access to oxygen, resulting in biogas which can be used as fuel for vehicles or for electricity and heat production, and a residual product which can be used as fertilizer. When composted, biodegradable waste is degraded with access to oxygen, and the residual product can be used as a soil amender.

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electricity prices due to marginal pricing, where the marginal power producer is coal condensing power in the European system, further explained by Trygg and Karlsson (2005).

European Differences in Waste Management and Use of District Heating This section presents some figures with regard to the amount of district heating in different European countries and waste management methods. Figures for electricity and heat output from waste incineration in different European countries are given. The aim is to investigate if any unambiguous trends can be seen in this material; is there a correlation between high DH production and/or high market share and high proportion of energy recovery as a waste treatment method? In Sweden this is the case, but what about other European countries?

100% 80% 60% 40% 20%

Au st Bu ria lg ar Cr ia oa ti Cz a e De ch nm a Es rk to n Fi i a nl an Fr d a G nce er m a Hu ny ng ar y Ita Ic ly el an d La Li tvi t a Ne hua th nia er la n No d s rw a Po y l Ro and m a Sl nia ov a Sw kia Sw ed itz en er la nd

0%

Coal

Oil

Natural gas

Renewables

Waste

Others

Figure 3. Fuels used for DH in the countries surveyed in a report by Euroheat and Power (2003).

Figure 3 shows the amount of fuel used for DH production by some European countries. It can be seen that the supply differs between countries. Coal is the major fuel used in the Central and Eastern European (CEE) countries and natural gas is also widely used; and the two fuels account for about 85% of the total supply. The CEE countries show a less diversified supply than the old EU member states and a large untapped potential exists for using more heat from waste incineration, renewables, and industrial surplus heat. As regards the proportion of DH produced in CHP plants, this is high in the old member States (64-94%) with the exception of Sweden.10 In the CEE countries, the proportion is lower (35-72%).

10

One reason for this is the historically low electricity prices in Sweden (Sjödin, 2002) and (Trygg and Karlsson, 2005).

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Kristina Holmgren Table 1. Treatment methods for municipal waste in European countries 2002 in 000s of tons (Eurostat, 2005)11

Belgium Czech Republic Denmark Germany Estonia Greece Spain France Ireland Italy Cyprus Latvia Lithuania Luxembourg Hungary Malta Netherlands Austria Poland Portugal Slovenia Slovakia Finland Sweden UK Bulgaria Romania Turkey Iceland Norway Switzerland

Recycling

Composting

Energy recovery

Incineration, destruction

1442 175 796 17250 13 375 3811 4715 463 3897 : 35 : : 67 : 2133 : 116 252 87 37 659 1295 3733 : 170 : 19 507 :

1088 122 555 7844 2 32 3914 4208 34 7335 : 24 : : 47 : 2365 : 215 135 11 39 : 354 1423 : : 383 3 225 :

1493 398 2008 153 0 : 1567 10235 : 2587 : 55 : : 288 : 3125 490 : 944 5 91 201 1675 2674 : : 9 7 492 :

134 3 : 11673 0 : : 875 : 111 : 0 : : : : : : 36 : 0 65 0 : 7 : : 0 3 :

Landfill

Total

594 2097 215 11266 419 4233 14723 12991 1967 18500 450 657 1000 : 3907 188 810 1500 10142 3388 699 1192 1512 825 27545 3188 6695 24573 245 482 80

4761 2845 3587 52532 553 4640 : 33024 2724 29929 500 866 1000 : 4646 187 9900 4634 10509 4618 956 1524 2372 4172 33535 3945 8365 33324 293 3061 4900

Figure 4 shows the total DH production in several European countries together with its share of the heat market. It can be seen that Poland and Germany are the largest producers. The highest market shares exist in some Nordic countries, along with some CEE countries.

11

The data in the Recycling, Composting, Energy recovery, Incineration destruction, and Landfill columns are taken from “Treatment of municipal waste”. The data in the Total column is taken from “Generation of municipal waste”. These were obtained from the Eurostat website. The data differs somewhat in some cases. This is done in order to compare data, to see whether anything has been omitted.

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Profu (2004) identifies a number of “key-factors” when assessing environmental impact of waste incineration, where one is energy recovery per ton waste. Figure 5 shows the extent to which the useful energy content of the incinerated waste is taken care of in a number of countries. Sweden has the highest energy recovery of the countries surveyed, mainly due to the country’s extensive DH network. The efficiency of using waste as a fuel varies between the countries surveyed. It should be noted, however, that if the data in the diagram were recalculated into oil equivalences, countries would show more similar figures. 120

100 90 80 70 60 50 40 30 20 10 0

100 80 60 40 20

DH production

UK

S witz erland

S weden

S lov ak ia

Rom ania

P oland

Norway

Lithuania

Netherlands

Latv ia

Italy

Ic eland

Hungary

G erm any

Franc e

Finland

E s tonia

Denm ark

Cz ec h

Croatia

B ulgaria

A us tria

0

DH market share

Figure 4. DH production (TWh) and DH market share (%) in the countries surveyed by the report in Euroheat and Power (2003).

3,5 3 2,5 2 1,5 1 0,5

Ita Ne ly th er la nd s Sp G re ai n at Br it a P o in rtu g Hu a l ng ar y

Sw ed en Au Sw stri it z a er la nd No rw De a y nm ar k Fr an ce G er m an y

0

Figure 5. Energy recovery by waste incineration (International Solid Waste Association, 2002; Swedish Association of Waste Management, 2000)

Table 1 shows different waste treatment methods in the European countries. The statistics are not exhaustive because not all data is available. Nonetheless, some comments can be made. Regarding the correlation between high amount of DH and energy recovery, this can mainly be seen in Sweden and Denmark. One thing that separates Denmark from Sweden is

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the high proportion of total electricity production that comes from CHP plants; about 40% in Denmark compared to around 8% in Sweden. The countries in CEE with a high amount of DH and/or large market share (the Baltic countries, Poland, the Czech Republic, Slovakia, and Romania) have not evolved their waste management sector and landfill is still the dominating treatment method. Some countries have a large proportion of heat from waste incineration in the DH systems, but the total amount of DH and/or market share is low, such as France, Norway, Italy and Switzerland. For Germany, the data is contradictory. In Table 1, it would appear that incineration is used mainly as a destruction method but as Figure 3 shows, some of the heat comes from waste. What can be said is that Germany has put a lot of effort into developing their material recycling. In general for Table 1, it can be said that waste treatment differs widely between countries and many still rely heavily on landfill.

Impact on Waste Incineration in Sweden of Waste Trade with Some European Countries Trading in waste in the European Union is regulated (European Council, 1993) and waste is divided into different categories: green, yellow and red. Green waste includes e.g. wood chips, logging residues, pellet, tall oil and sorted fractions of plastics, paper and rubber; imports of waste in this category do not have to be registered. Examples of yellow waste are chemically treated used woods, mixed fractions of used wood, paper, rubber and plastics, and municipal solid waste. Red waste is e.g. waste containing or contaminated with polychlorinated biphenyl (PCB) or polychlorinated dibenzo-dioxin. The information on what type of waste the categories include is taken from Ericsson and Nilsson (2004). The authors estimated imports of green waste in 2000 at 760,000 tons. The Swedish Environment Protection Agency must approve imports of yellow and red fractions. Imports of yellow waste increased from 200,000 tons in 1999 to 430,000 tons in 2002 (Olofsson et al 2005). Olofsson et al analyse which factors lie behind Swedish yellow waste imports, mainly intended for use in waste incineration plants with energy recovery. Both factors in the waste management system and the energy system are analysed. Five countries account for almost all imports to Sweden: Denmark, Finland, Germany, Norway, and Holland. The following factors may be significant; − − −

−

12

The infrastructure in Sweden, with DH systems that can utilise the heat, thus raising energy recovery significantly Energy taxation on fossil fuels is high12 in Sweden, and this increases the value of heat. Different types of bio fuel are the most common alternative for the base supply of heat. This means that clean fractions of waste are suitable to combust in existing plants, since the fuels are similar in composition. The quality of the imported waste has been higher than waste from Sweden, but this is starting to level out due to stricter sorting requirements in Sweden.

The carbon dioxide tax is at present 0.1 €/kg.

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Taxes on waste and a ban on landfill are also driving factors. Norway and Denmark both have taxes on waste incineration.

All the above factors lead to a difference in gate fees. The authors assume that in the future, the predominant factor to decrease the driving factors for import to Sweden would be the introduction of a waste incineration tax. A change in energy taxation in order to better fit in to the European Union legislation could also have a significant impact. In Sweden, business is divided into different sectors, with differentiated energy tax levels. This may be in conflict with the EU’s rules with regard to state aid, but Sweden has been granted temporary exemption. If the differentiation were changed and the same rules were valid for the whole of the business sector, the value of heat would be lowered, since the high taxes on fossil fuels would be lowered. Instead, it is suggested that there would be taxation on heat for consumers (Ministry of Finance, 2003). Table 2 shows the gate fees in Sweden for different treatment options for municipal waste. As can be seen, there is great variation between plants. Table 2. Gate fees for municipal waste, including VAT and taxes (Swedish Association of Waste Management, 2005b) Treatment method Cost (€/ton)

Landfill 74-128

Incineration 32-64

Biological treatment 43-106

Impact on Waste Incineration of Trade in Electricity The objective of the directive (European Union, 2003a) on a common internal electricity market is to open up the electricity market by subjecting it to competition. The reason for this is to increase efficiency in the energy sector. Industrial consumers can choose their supplier from July 1st 2004 and all consumers from July 1st 2007. The European Commission publishes a yearly report about the implementation of the internal market (European Commission, 2004) and that report states that the result of the implementation so far is unsatisfactory. One reason is barriers to cross-border trade, e.g. market structures and the need for additional investments in infrastructure. However, the report states that these problems must be solved. The impact of this directive in Sweden is that electricity prices will increase due to harmonisation with the electricity prices in continental Europe, which are higher than in Sweden. This is further described in Trygg and Karlsson (2005). Higher electricity prices increases interest in producing electricity in the DH systems, and naturally also interest in electricity production in waste incineration plants. It also effects the cost of heat in the DH networks. A higher electricity price reduces the cost of heat from CHP plants and their possibility to compete with other plants also improves. Waste incineration plants are base suppliers of heat due to their negative operational costs and the need to treat the waste. However, in the DH network of Göteborg (Holmgren, 2006), where the municipal

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energy utility buys heat from a waste incineration plant13 and also waste heat from industries, the municipal utility had a better negotiation position towards those companies when they invested in a natural gas fired CHP plant assuming electricity prices harmonized with those on the continent.

DISCUSSION OF TWO POLICY INSTRUMENTS Two policy instruments will be discussed in this section: the introduction of a tax on incinerated waste and the green electricity certificate system. The aim here is to show how policy instruments in one system affect the other, and the difficulties in handling the double function of waste incineration as a supplier of heat and/or electricity and as a waste treatment method.

Introduction of a Tax on Incinerated Waste in Sweden A government investigation on a tax on incinerated waste was presented recently (Ministry of Finance, 2005b), and a proposal of the tax was incorporated in the government budget proposition (Ministry of Finance, 2005c). The proposal is that waste should be incorporated in the existing energy taxation system by taxing the fossil content of the waste, meaning e.g. plastic packaging. However, at the time of writing, the tax has been postponed due to difficulties in measuring the fossil content in municipal waste. Table 3 shows the level of the tax on incinerated waste and how it applies to different energy conversion units. The design of the tax is in accordance with how existing energy taxation is applied to the DH sector; with a carbon dioxide tax and an energy tax, which is not applied to electricity production, since electricity is taxed for the consumer (industrial consumers are exempt), heat from hot water boilers is taxed in full, and heat from CHP plants is taxed at deducted levels as is heat to industrial consumers. For a more detailed description of energy taxation, see e.g. Holmgren (2006). It can also be noted that the DH networks are part of the emission allowance trading systems, and the plants included will therefore probable be granted additional deductions of carbon dioxide taxes. However, since waste incineration plants are not included in the trading system, this is not included here. The description of the assignment to carry out the governmental investigation of this tax includes several goals that should be taken into consideration. How the tax steers according to the waste hierarchy and to make material recovery including biological treatment more economically competitive is important, but also impacts on the DH networks and the incentive for CHP production from waste incineration. The problem is that the goals that are enumerated conflict.

13

In this case, another company, co-owned by several neighbouring municipalities owned the waste incineration plant and sold the heat to the utility operating the DH network.

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Table 3. Waste incineration tax as proposed (Ministry of Finance, 2005b). Energy tax (€/ton waste)

Carbon dioxide tax (€/ton waste)

Fossil content 100% Hot water boiler 16 355 Condensing power plant 0 0 14 51-62 CHP plant Fossil content: 14% of total weight (assumed value for municipal waste) Hot water boiler 2 45 Condensing power plant 0 0 CHP plant 0 6.5-8

Total (€/ton waste)

371 0 51-62 47 0 6.5-8

In the waste incineration tax proposal, resulting from the government investigation, the energy system perspective is the predominant; waste is seen primarily as a fuel, and therefore the main objective is that waste taxation be harmonized with energy taxes on other fuels. The investigation states that the fossil content of waste is subsidized in comparison to fossil fuels and that the value of the subsidization of biomass fuels is lessened if there is no tax on incinerated waste. This is corrected if the tax on incinerated waste is designed in this way, and it also provides the incentive for CHP production in waste incineration plants which has hitherto been lacking. The EU directive on promotion of CHP (European Union, 2004a) has influence over this. When summarizing the proposal, it can be said that the energy perspective has been given first priority and the waste management priority second. The only fraction which will have an increased incentive to material recover is various plastics. This fraction is appropriate for material recycling in an energy efficiency perspective; an earlier study has shown large energy savings when recycled plastic material is used instead of virgin material (Holmgren and Henning, 2004). Another study has analysed the consequences for a municipal energy utility of investing in waste incineration if a tax on incinerated waste were introduced. (Holmgren and Gebremedhin, 2004). Tax levels of 11 and 42.5 €/ton were analysed, since those were the levels proposed in an earlier government investigation (Ministry of Finance, 2002). The conclusion was that at the tax level of 11 €/ton, the investment was still profitable for the utility, but at the 42.5 €/ton level, the investment was not profitable. Note that in Table 3 these levels are in the proximity of the levels proposed for plants with CHP production and hot water boilers respectively. The prerequisite for the results is naturally that the utility can not raise the gate fee for receiving the waste. The results indicate, however, that at these tax levels, other treatment options begin to be of interest. Other questions which are raised concern the impact on gate fees of waste incineration plants. Plants with electricity production could maintain lower gate fees than other plants. Would that mean transportation of waste to those plants? This, however, is contradicted by the lack of waste treatment capacity (Swedish Association of Waste Management, 2004), due to waste management regulations. Another issue is to what extent the energy utilities will raise their gate fees to let consumers shoulder the increasing costs. Most existing plants 14

Electrical efficiency in the interval 15-28%.

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without electricity production can not easily convert to CHP production since they consist of hot water boilers,15 and conversion would virtually mean building a new plant. Of the planned waste incineration plans, all have electricity production16 (Swedish District Heating Association, 2005). One question in a waste management perspective is what will happen in terms of encouraging material recovery and biological treatment, in accordance with the waste hierarchy, since this opportunity to increase incentive was not taken.17

Green Electricity Certificates and Waste Incineration The green electricity certificate system is designed to increase electricity produced by renewables (Ministry of the Environment, 2003a, b). The certificate system is influenced by the directive on increased electricity from renewables (European Union, 2001). The producers of electricity receive a certificate when they produce electricity in approved conversion units. These are wind power, solar power, geothermal power, tidal power, hydropower in new or small plants (installed after the end of 2002, and also increased power in old plants renovated after April 2003 and hydropower in plants with a maximum capacity of 1.5 MW), biomass, peat, sorted wood waste from demolition waste, and electricity produced from biogas. It is also proposed that animal fat, meaning residual products from the food industry, should receive certificates (Ministry of Finance, 2005c). Consumers will need a quota of certificates in relation to their total electricity consumption, creating a demand for certificates and thus giving them an economic value. The aim is to increase annual electricity production from renewable energy sources by 10 TWh between 2003 and 2010. The system ends in 2010, but a proposal to extend it to 2030 is in place (Ministry of Sustainable Development, 2005). Electricity produced from municipal waste does not receive certificates in the Swedish certificate system, even if municipal waste is estimated to be of about 80% biological origin. If municipal waste were to be included, it would further increase the incentives for CHP in waste incineration plants since it pays off for every produced MWh of electricity. In the proposed tax on incinerated waste, the main issue is to be classified as a CHP plant, and in order to be so, the quota between electricity and heat needs to be at least 20% (Ministry of Finance, 2005b). The issue of whether municipal waste should receive electricity certificates has been debated since the electricity certificate system was originally designed and in the government investigation on a tax on incinerated waste (Ministry of Finance, 2005d) the question is analysed once again. The conclusion is that the new tax on incinerated waste is enough to steer towards increased CHP in waste incineration plants and if electricity certificates were given for municipal waste, it could steer waste of biological origin towards incineration and that would not comply with Swedish waste management goals.18 Again, the conflict between the goals in waste management and in the energy system can be seen. From an energy system viewpoint, it is logical to implement electricity certificates for municipal waste. It would increase electricity production in waste incineration which is in line with the 15 16 17 18

Personal contact with Anders Hedenstedt, Swedish Association of Waste Management. Personal contact with Anders Hedenstedt, Swedish Association of Waste Management. Again; except for fractions of plastic waste. The Swedish goals for biodegradable waste state that at least 35% should be biologically treated by 2010 (Swedish Environmental Protection Agency, 2005).

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European directive on promotion of cogeneration (European Union, 2004a). When the tax on incinerated waste is introduced, it is deemed important to remove the subsidies that the fossil part of municipal waste has enjoyed in comparison to fossil fuels. When the electricity certificate system is analysed, it is not important to insert the biological part in the system which benefits biomass fuels. When it comes to green electricity certificates, the government investigation states that the waste management goals are more important than the goals of the energy system. The directive on electricity from renewables (European Union, 2001) provides scope for interpretation by member states, e.g. as regards which sources should be included in a certificate system. A voluntary certificate system exists in Europe, The Renewable Energy Certificate System19 (RECS) which in contrast to the Swedish system does include municipal waste. This shows that opinions as to how to classify waste in terms of whether it is a renewable or not differ throughout Europe.

MODELS AS DECISION SUPPORT Various models are often used as decision support tools, e.g. when municipalities make infrastructural decisions, such as waste treatment capacity and energy utility plants. This section describes some models based on system analysis. The models have been used to assess waste management systems and waste incineration and the common theme is the dilemma of the two purposes waste treatment and production of heat and sometimes electricity, and how to handle this. System analysis can be a mean to assess complex systems in order to e.g. determine how available resources should be used to satisfy the aim of the system or to evaluate environmental impacts of various measures. A model can be built that should include the essential features of the system. By building a model, understanding and knowledge of the system and the correlation between components in the system is gained.

Models and How to Handle the Double Function of Waste Incineration The method used in earlier studies carried out by the author (Holmgren and Bartlett, 2004; Holmgren and Gebremedhin, 2004; Holmgren, 2006) is energy system modelling, using the MODEST model (Henning 1998; 1999). MODEST is a linear programming model which minimizes the cost of supplying heat and/or power demand during the analysed period. The main purpose of the model is to find suitable investments, but it can also be used to optimize the operation of existing plants. The results from these studies are mainly how waste functions as a fuel in the district heating system, e.g. the impact on other fuels used, the cost of supplying heat with different amounts of waste used as fuel, and the amount of electricity produced in the DH networks. The effects of various policy instruments are also an appropriate issue to assess. The influence of the waste management system in the model is mainly via economic signals as regards the cost of waste as a fuel. Limits on amount of

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available waste is also set. When analyzing the results, it is vital to be aware that also considerations, more related to the waste management sector, should be included. A study has also been made that has broadened the scope by comparing waste treatment options from an energy efficiency viewpoint (Holmgren and Henning, 2004). Assuming that there is a district heating system that can utilize the heat, which fractions of the waste are suitable to energy recover and which to material recover? Another example of a study with the energy system in focus is Sahlin et al (2004), which analyses the impact on Swedish district heating systems as a whole, using a questionnaire and a simulating energy model named HEATSPOT. Other methods have the waste management system in focus, as shown e.g. by Sundberg et al (1994). The paper describes the model MIMES/WASTE, which seeks the most costefficient way to treat waste. Another study has linked MIMES/WASTE with an energy system model, MARTES, by using both models in two case studies (Olofsson, 2001). Life cycle assessment (LCA) is a widely used method for evaluating the environmental impact of products and services (Rydh et al, 2002). How to perform an LCA is laid down in ISO standards. The methodology in short has four steps: 1. Goal and scope definition 2. Inventory analysis, where data is compiled 3. Life cycle assessment involving classification of data to different environmental impacts;20 characterization, where the data is analysed as to the extent to which they contribute to different impacts; and valuing or weighting. The step of valuing is however in question since it is considered to be subjective. 4. Interpretation of results. One model for assessing waste management options based on LCA methodology is ORWARE, see e.g. Eriksson et al (2002). This model handles the double functions of waste incineration by compensatory systems, in line with LCA methodology. A compensatory system, e.g. for waste incineration, apart from the function of waste treatment, also means district heating and/or electricity. To assess the robustness of the results, a sensitivity analysis of these compensatory systems is recommended, e.g. if district heating is produced by biomass fuel or oil. Finnveden and Ekvall (1998) compare LCA studies of recycling versus incineration of paper, and show the importance of assumptions made with regard to compensatory systems and also take up the question of biomass; what is made of the saved biomass when recycling paper? This question indicates a need to define how biomass should be regarded; should it be regarded as a scarce resource? A number of studies have attempted to estimate the potential biomass supply. Ericsson and Nilsson (2006) have assessed the potential in the 15 old EU countries (EU15), 8 newcomers21 and 2 candidate countries22 (ACC10) and also Belarus and Ukraine, and compared it with the EU’s targets for increasing the proportion of the total primary energy supply produced with biomass. Their assessment shows that, subject to certain restrictions on land availability, the potential is up to 11.7 EJ/year in the EU15 and 5.5 EJ/year in the 19 20 21 22

More information can be found at www.recs.org (November 2005). Such as greenhouse gases, eutrophication, acidification. Cyprus and Malta are not included. Bulgaria and Romania.

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ACC10. These figures can be compared with the fact that total energy supply in the EU15 in 2001 was 62.6 EJ. There are no resource limitations in meeting the EU target of 5.6 EJ/year in the EU15 by 2010, though it will probably not be met due to slow implementation of the renewable energy policy. Berndes et. al. (2003) are reviewing 17 studies on the contribution of biomass in future global energy supply. Both demand-driven studies23 and resource studies24 were reviewed. The resource studies showed large variations in the amount of biomass fuels. The studies with the highest assumptions assumed vast areas of Africa to be given over to energy crop production with exports to the rest of the world. The article criticizes the studies for not including other environmental effects of such expansion, such as biodiversity, and social factors are also overlooked. These studies give an indication that biomass utilization could increase substantially; this could, however, lead to environmental and social problems which are not taken into account when, for example, making a study where biomass fuel replaces fossil fuel as a compensatory system for district heating production, hence indicating lower environmental concerns. This is a significant issue, since it has been shown that these assumptions are often crucial for the results in LCA studies. One drawback of using MODEST when analyzing waste incineration is that few environmental effects have been taken into account. In earlier studies (Holmgren and Bartlett, 2004; Holmgren and Gebrenedhin, 2004; Holmgren, 2006), only carbon dioxide emissions from the analysed DH networks have been calculated. One solution could be to use external costs of environmental effects, and include these costs in the optimization calculations of the D networks. This has been done by Carlsson (2002). In that study, external cost data was obtained from the European Union’s ExternE-project.25 The basic idea behind the concept of external cost is that electricity and heat production give rise to several negative external effects,26 such as climate change, acidification and health impacts. The cost of these effects should be internalized in the price of the energy supply, otherwise a suboptimal consumption of energy occurs from a socio-economic perspective. This can be compared to the step of valuing or weighing in the LCA methodology, since that is essentially also to put a value on environmental effects. However, this step is not really accepted in LCA methodology since it is considered to be subjective and the recommendation is to use it with care.

CONCLUSION The double function of waste incineration, both as a waste treatment method and a supplier of electricity and/or heat is discussed in this chapter. A positive impact in one of the systems may be negative in the other, and strategies and goals in the two sectors can conflict. The main findings in this chapter are as follows.

23

24

25 26

The meaning of demand-driven studies is the potential of energy from biomass in competition with other energy carriers. The meaning of resource-driven studies is the possibility to produce biomass for energy purposes in competition with other land uses, such as food production. Information about the ExternE project can be found at http://www.externe.info/ Positive external effects, for example on local employment, can also occur.

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−

−

−

−

Sweden has extensive DH networks and therefore better possibilities to efficiently recover the energy content in the waste than countries with a less developed infrastructure. There is a correlation between extensive DH networks and substantial incineration as waste treatment method in Sweden, and the connection is both historical and organisational. This correlation can not be unambiguously shown to exist in any other EU country. In this context, Sweden differs from other Western European countries, since relatively little DH is produced in CHP plants. Waste incineration can decrease possibilities for producing CHP in DH networks and this can be seen as a conflict between the need to treat waste in an acceptable way and the goal of more CHP production in the energy system. There is a conflict in the European Union between the internal market and waste management policy, for example that waste should be treated close to its origin. This has been solved by prohibiting exports of waste for disposal but not for recovery. A shortcoming in the directives is that they do not clearly define what an energy efficient waste incineration plant is and hence not when a waste incineration plant should be defined as recovery versus destruction. The conflict between waste management goals and energy system goals when designing policy instruments has been shown. When designing the tax on incinerated waste, the energy system perspective was the predominant factor, the main objective being to harmonize taxes on incinerated waste with taxes on other fuels. The incentive for increasing material recovery and biological treatment was set aside, except in the case of plastic waste. In the design of the electricity certificate system, the waste management goals, for example more biological treatment, prohibits waste incineration plants from receiving certificates even if this would increase the incentive to produce CHP, consistent with the goals for the energy system. The double function is also addressed when different models for assessing waste incineration are reviewed; the importance of being aware of this and the impacts of different assumptions are discussed. Various models deal with the double function in different ways, and have their own strengths and weaknesses. It is also essential to be aware of the importance of assumptions. A model’s construction and the results from it should be seen as way of gaining knowledge of the system and as a support in decision-making. When actual decisions are to be made, there are other aspects that can be of importance that has not been included in the model.

ACKNOWLEDGMENTS The work was carried out under the auspices of The Energy Systems Programme, which is financed by the Swedish Foundation for Strategic Research, the Swedish Energy Agency and Swedish Industry. Tekniska Verken i Linköping AB is acknowledged for their financial support. The author is grateful to Maria Saxe, Mats Bladh and Björn Karlsson for valuable comments on the chapter.

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European Union. 2003c. Council Directive 2003/87/EC establishing a scheme for greenhouse gas emission allowance trading within the Community and amending Council Directive 96/64/EC. Brussels, Belgium. European Union. 2004a. Directive 2004/8/EC on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC. Brussels, Belgium. European Union. 2004b. Directive 2004/12/EC amending Directive 94/62/EC on packaging and packaging waste. Brussels, Belgium. Eurostat. 2005. Statistical data obtained from: http://epp.eurostat.cec.eu.int/portal/ page?_pageid=1090,30070682,1090_33076576&_dad=portal&_schema=PORTAL. Site visited December 2005. Finnveden G and Ekvall T. 1998. Life-cycle assessment as a decision-support tool – the case of recycling versus incineration of paper. Resources, Conservation and Recycling 24:235256. Henning D. 1998. Cost optimisation for a local utility through CHP, heat storage and load management. International Journal of Energy Research 22:691-713. Henning D. 1999. Optimisation of local and national energy systems: development and use of the MODEST model. Dissertation No. 559, Linköping Institute of Technology, Linköping, Sweden. Holmgren K and Bartlett M. 2004. Waste incineration in Swedish municipal energy systems – modelling the effects of various waste quantities in the city of Linköping. In: Afghan NH, Bogdan Z, Duic N. Editors. Sustainable development of energy, water and environment systems. Proceedings of the Conference, 2-7 June 2002, Dubrovnik, Croatia. Holmgren K and Gebremedhin A. 2004. Modelling a district heating system: introduction of waste incineration, policy instruments and co-operation with an industry. Energy Policy, 32:1807-1817. Holmgren K and Henning D. 2004. Comparison between material and energy recovery of municipal waste from an energy perspective. A study of two Swedish municipalities. Resources, Conservation and Recycling, 43:51-73. Holmgren K. 2006. The role of a district heating network as a user of waste heat supply from various sources – the case of Göteborg. Applied Energy, in press. Hrelja R. 2006. I hettan från ångpannan – vetenskap, politik och miljö kring en kommunal energianläggning under två decennier. (In the heat from the steam boiler – science, politics and environment surrounding a municipal energy facility during two decades, in Swedish) Manuscript, coming dissertation from Linköping Universitet. International Solid Waste Association. 2002. Energy from Waste, State-of-the art Report, Statistics 4, Edition January 2002. Copenhagen, Denmark. Korobitsyn M.A, Jellema P and Hirs G.G. 1999. Possibilities for gas turbine and waste incinerator integration. Energy 24:783-793. Ministry of the Environment. 1994. Förordning (1994:1205) om producentansvar för returpapper (Ordinance 1994:1205 on producer responsibility for newspaper, in Swedish). Stockholm, Sweden. Ministry of the Environment. 1997. Förordning (1997:185) om producentansvar för förpackningar (Ordinance 1997:185 on producer responsibility for packaging, in Swedish). Stockholm, Sweden.

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Ministry of the Environment. 2001. Förordning (2001:512) om deponering av avfall (Ordinance (2001:512) on landfill of waste, in Swedish) Stockholm, Sweden. Ministry of the Environment. 2003a. Lag (2003:113) om elcertifikat (Law (2003:113) on electricity certificates, in Swedish). Stockholm, Sweden. Ministry of the Environment. 2003b. Förordning (2003:120) om elcertifikat (Ordinance (2003:120) on electricity certificates, in Swedish, Stockholm, Sweden. Ministry of Finance. 1994. Lag (1994:1776) om skatt på energi. (Law (1994:1776) on tax on energy. Stockholm, Sweden. Ministry of Finance. 2002. Skatt på avfall idag – och i framtiden (Tax on waste today – and in the future, in Swedish) SOU 2002:9, Fritze, Stockholm, Sweden. Ministry of Finance. 2003. Svåra skatter: betänkande från Skattenedsättningskommittén. (Difficult taxes, in Swedish). SOU 2003:38, Stockholm, Sweden. Ministry of Finance. 2005a. Lag (2005:962) om ändring i lagen (1999:673) om skatt på avfall (Law (2005:962) on changes in the law (199:673) governing waste tax, in Swedish), Stockholm, Sweden. Ministry of Finance. 2005b. BRASkatt? – beskattning av avfall som förbränns (GOODtax? – taxation of incinerated waste, in Swedish.) SoU 2005:23. Stockholm, Sweden. Ministry of Finance. 2005c. Budgetpropositionen för 2006 (Budget proposal 2006, in Swedish) Prop, 2005/06:1. Stockholm, Sweden. Ministry of Finance. 2005d. BRASkatt?- beskattning av avfall som deponeras (GOODtax? – taxation of landfilled waste, in Swedish) SOU 2005:64. Stockholm, Sweden. Ministry of Sustainable Development. 2005. Förslag om ett utvecklat elcertifikatsystem. Proposal for a developed electricity certificate system, in Swedish) Ds 2005:29, Stockholm, Sweden. Olofsson M. 2001. Linking the Analysis of Waste Management and Energy Systems. ISRN CTH-EST-R-01/5-SE, Department of Energy Conversion, Chalmers University of Technology, Göteborg, Sweden. Olofsson M, Sahlin J, Ekvall T and Sundberg J. 2005. Driving forces for import of waste for energy recovery in Sweden. Waste Management and Research 23:3-12. Palm J. 2004. Makten över energin – policyprocesser i två kommuner 1977-2001. (Influence over energy – the process of policy in two municipalities 1977-2001, in Swedish). Linköping Studies in Arts and Science 289. Linköpings Universitet, Linköping, Sweden. Profu. 2004. Evaluating waste incineration as treatment and energy recovery method from an environmental point of view. Collected from home page www.profu.se. Rydh CJ, Lindahl M and Tingström J. 2002. Livscykelanalys – en metod för miljöbedömning av varor och tjänster. (Life cycle assessment – a method for environmental assessment of goods and services, in Swedish), Studentlitteratur, Lund, Sweden. Sahlin J, Knutsson D and Ekvall T. 2004. Effects of planned expansion of waste incineration in the Swedish district heating systems. Resources, Conservation and Recycling 41:279292. Sjödin J. 2002. Swedish District Heating Systems and a Harmonised European Energy Market – Means to Reduce Global Carbon Emissions. Dissertation No. 795. Linköping Institute of Technology, Linköping, Sweden. Sundberg J, Gipperth P and Wene C-O. 1994. A systems approach to municipal solid waste management: a pilot study of Göteborg. Waste Management and Research 12:73-91.

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Swedish Association of Waste Management. 2000. Svensk Avfallshantering 2000 (Swedish Waste Management 2000, in Swedish), Malmö, Sweden. Swedish Association of Waste Management. 2004. Avfallsförbränning. Utbyggnadsplaner, behov och brist. (Waste incineration. Expansion plans, capacity need and lack thereof, in Swedish) RVF-report 04:02. Malmö, Sweden. Swedish Association of Waste Management. 2005a. Avfall blir värme och el. En rapport om avfallsförbränning. (Waste turn into heat and electricity. A report on waste incineration, in Swedish). RVF-report 2005:02. Malmö, Sweden. Swedish Association of Waste Management. 2005b. Svensk avfallshantering 2005 (Swedish Waste Management 2005, in Swedish), Malmö, Sweden. Swedish District Heating Association. 2005. Kraftvärme och dess kopplingar till elcertifikatsystemet. (Combined heat and power and the connection to the electricity certificate system, in Swedish), Sweden. Swedish Energy Agency. 2004. Energy in Sweden 2004. Eskilstuna, Sweden. Swedish Environmental Protection Agency. 2005. Strategi för hållbar avfallshantering. (Strategy for sustainable waste management, in Swedish), Stockholm, Sweden. Trygg L and Karlsson B.G. 2005. Industrial DSM in a deregulated European electricity market – a case study of 11 plants in Sweden. Energy Policy 33:1445-1459.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 221-234 © 2006 Nova Science Publishers, Inc.

Chapter 7

ARTIFICIAL AGGREGATE MADE BY CEMENTITIOUS GRANULATION OF WASTE INCINERATOR FLY ASH R. Cioffi1, F. Colangelo1, F. Montagnaro2 and L. Santoro2* 1

Dipartimento per le Tecnologie, Università di Napoli Parthenope, Napoli, Italy 2 Dipartimento di Chimica, Università di Napoli Federico II, Napoli, Italy

ABSTRACT The waste employed in this work comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both fly ash samples coming from these two equipments have been individually employed. Ash from waste incineration plant is classified as hazardous and cannot be utilized or even landfilled without prior treatment. This paper reports the results of an extensive investigation on stabilization/solidification of the above ash samples by addition of hydraulic binders in a granulation equipment. A rotary plate granulator was used with binders based on cement, lime and coal fly ash. Granulation was carried out with several mixes in which the ash content was up to 70%. In some cases, the granules obtained in this way are suited for matter recovery by reusing the waste for the manufacture of building materials. To achieve this in most cases, two-step granulation is required with pure binder being used in the second one. In this way the granules from the first step can be encapsulated within an outer shell able to improve the technological and leaching properties. The possibility to get matter recovery from incinerator ash is a crucial issue for making the granulation process environmentally and economically sound. In fact, the most direct application of granules is in the field of artificial aggregates for road construction and concrete manufacture. The granules obtained from the treatment of fly ash samples have been tested to assess their physicomechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive

*

Corresponding author. Tel.: +39-081674028; fax: ++39-081674090. E-mail address: [email protected]

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INTRODUCTION In the last few years the use of aggregates in the different fields of civil engineering has been steadily growing and the Italian yearly demand for this material was estimated to be about 1.3·108 m3 in 2002 [1]. As a consequence, the resulting environmental impact is an issue that must be faced to have sustainable development in all the fields of civil engineering. The replacement (at least partial) of natural aggregates with artificial ones can help solve the above problem and also can address waste management towards matter recovery. This possibility is of great importance in the light of the increasingly high availability of industrial solid wastes, marine and lake sediments as well as construction and demolition wastes. So, it is not surprising that many papers can be found in the literature on the replacement of natural aggregate with unprocessed wastes from several different sources [1-14]. However, artificial aggregate of improved technological and leaching properties can be manufactured from reprocessed wastes according to specific treatments that can be of different type depending on the nature of the waste and on the characteristics of the desired product. Specifically, the waste properties that can be of concern are the physical nature (homogenous, heterogeneous, monolithic, granular, sludge), the structure (amorphous, crystalline, compact, porous), the chemical composition and the compatibility with binding matrices. On the other hand, the characteristics of the desired product that are of concern are those linked to the specific use the aggregate is intended for. Among the above waste and aggregate characteristics, probably the most important one is the waste chemical composition. The reason for this is that, depending on this characteristic, the waste can or cannot be chemically involved in the treatment required for aggregate manufacture. Of course, this issue can affect not only the product quality, but also the release of the contaminants that may be contained in the raw waste. In the light of the above considerations, it can be said that a proposed process for aggregate manufacture from waste must be validated from the three-fold point of view: chemical, technological and environmental. From the chemical point of view it is important to understand how the waste components (pollutants included) are involved in the chemical processes that take place during waste treatment. That is, some waste components can be actively involved in the formation of the neo-formed phases and also the pollutants can be entrapped within these phases by means of chemical mechanisms such as diadochy, chemisorption, reprecipitation, etc. Alternatively, the waste components (pollutant included) can retain their chemical nature and in such a case the treatment would only rely on physical entrapment (micro- and macroencapsulation). From the technological point of view, it is important to assess the suitability of the treated waste to the application for which the treatment is intended. Of course, this requires the measurement of the pertinent physical and mechanical properties (density, porosity,

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compressive strength, etc.) and the assessment of their compliance to the technical specifications pertinent to the proposed application. Finally, from the environmental point of view it is important to assess the pollutants release that can take place during the artificial aggregate lifetime. Of course, under this point of view, the long-term release behavior can only be predicted, and, to this scope, proper basic characterization leaching tests can be helpful. Tests of this type can be static, dynamic, continuous, and can make use of leachants of different composition. Their scope is the understanding of the aggregate behavior, even at long-term, in any possible application scenario. Of course, these tests are to be carried out in addition to compliance tests which, different from country to country, are required for any proposed application. Artificial aggregates can be manufactured by means of two types of processes: cementbased granulation and high temperature sintering. Of these, the latter has been widely studied and the pertinent literature is rich of applications in which many waste materials proved to have potential for use as feedstock: bottom and fly ashes from combustors and municipal solid waste incinerators, metallurgical slags, dust from furnace, mine and quarry tailings, sediments, shredder waste, etc.[14-20]. On the other hand, although cement-based granulation processes have not yet been studied equally deeply, their suitability for the manufacture of artificial aggregates is undoubtedly worthy of consideration. First of all, it is well known that the treatment of wastes (often hazardous) largely relies on cement-based stabilization/ solidification processes which allow safer disposal and/or matter recovery for the manufacture of building materials [21-24]. Furthermore, the application of such processes has economical and environmental advantages due to the reduced energy requirement (process carried out at ordinary temperature) and the lack of secondary pollution (no gaseous emission is involved). As previously pointed out, cement-based processes can be equally well addressed towards safer disposal of the waste or matter recovery for the manufacture of building materials inasmuch as their twofold aim is to reduce the pollutants mobility and form monolithic products. The occurrence of physical and chemical stabilization/solidification mechanisms is necessary to warrant treatment effectiveness [21,22]. Under this point of view, it is useful to outline that cement-based processes have high potential and flexibility so that safer disposal may be favored in respect to matter recovery or vice versa depending on the optimization of the numerous variables that affect the same processes. In fact, the main operating conditions that can be optimized are: the binding matrix composition in respect to waste nature and composition, the waste/binder ratio, the time and temperature of curing, the use of specific additives and so on. More specifically, in addition to ordinary Portland cement and other established binders, alternative and innovative matrices have been successfully employed in many cases [25]. These alternative and innovative matrices can be obtained from industrial wastes such as coal fly ash, blast furnace slag, chemical gypsums. Furthermore, it has been recently proved that the use of additives based on organophilic bentonite allows the application of cement stabilization/solidification to wastes containing up to 55% organic matter [26,27]. In this article a cement-based granulation process has been studied for the manufacture of artificial aggregate starting from incinerator ash. This ash comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both the fly ashes coming from these two equipments have been individually employed. These ashes are classified as hazardous and cannot be utilized or even

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landfilled without prior treatment. The treatment investigated in this article is based on cement stabilization/solidification and makes use of a rotary plate granulator with binding mixes composed of cement, lime and coal fly ash. In addition to one-step granulation, two-step granulation was carried out to have end product of improved properties in view of reuse for artificial aggregate production. In the one-step granulation the waste is incorporated within the binding matrix in a measure ranging from 50 to 70%. In the two-step granulation a second step is carried out with pure binder to get the granules from the one-step process encapsulated within an outer shell able to improve the technological and leaching properties. The granules obtained from these processes have been tested to assess their physicomechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive (crushing) strength and leaching behavior. Moreover, concrete mixes have been prepared with some of the artificial aggregates made by granulation. Once hardened, these mixes have been tested from the technological point of view.

MATERIALS AND METHODS The ash employed in this work comes from an incineration plant located in Melfi (Potenza, Italy) in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and fly ash samples from both furnaces have been individually employed. According to the European Waste Catalog, this waste is given the code 19.01.13* and classified as hazardous. As such, it cannot be employed or even landfilled without prior treatment able to properly reduce its environmental impact. Table 1. Ash sample’s chemical composition, wt% Component Al2O3 Na2O K2O SO3 CaO Fe2O3 MgO MnO2 P2O5 TiO2 SiO2 ClCu, mg/kg Cd, mg/kg Pb, mg/kg Zn, mg/kg

Ash origin Rotary furnace 7.61 3.36 3.85 9.12 32.11 2.03 3.24 0.56 1.12 1.85 7.93 3.92 4927 62 3621 4643

Stoker furnace 3.89 2.62 2.32 7.12 41.23 1.02 1.69 0.11 0.53 0.42 11.06 1.41 2261 23 1720 2645

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Both the ash samples coming from the two different furnaces have been chemically characterized by means of the determination of the qualitative and quantitative compositions through X-ray fluorescence. The results are reported in Table 1 and show that the two ash samples have similar qualitative compositions. Differences can be mainly observed as far as the content of heavy metals of environmental concern is taken into account. Specifically, the ash sample from the rotary furnace incinerator has higher content of polluting metals, and this is a consequence of the different feed. Actually, the rotary furnace incinerator is fed with wastes from industrial processes, while the stoker furnace incinerator is fed with municipal and hospital wastes. Further characterization was carried out to determine the particle size distribution through laser light scattering. The results are reported in Table 2 and show that significant differences exist between the two ash samples. Specifically, the resulting volume weighted mean diameter is 36.6 µm for the rotary furnace incinerator ash sample and 64.4 µm for the stoker furnace incinerator ash sample. Table 2. Ash sample’s size distribution, vol% Size fraction, µm 120

Ash origin Rotary furnace 0.21 8.46 19.98 44.04 20.28 5.31 1.72

Stoker furnace 1.81 14.02 12.22 21.49 19.76 14.13 16.57

The ash samples leaching behavior has been determined through test UNI 10802 [28]. This test is in force in Italy and derives from European Union directives. It makes use of distilled water and, in the case of granular materials, extents up to 24 hours without leachant renewals. The amounts released in this test are reported in Table 3 for the metals of environmental concern. Despite the differences in heavy metals content, the release is similar for the two ash samples. Table 3. Metal release by raw ash samples, mg/L Metal Cd Zn Pb Cu

Ash origin Rotary furnace 0.63 8.27 1.86 1.09

Stoker furnace 0.54 7.32 1.53 1.08

The granules leaching behavior has been determined according to the compliance test in force in Italy that allows matter recovery from wastes [29]. This test is dynamic and makes use of distilled water with several leachant renewals up to 16 days.

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The other materials employed for the manufacture of the granules are a CEM II/A-L 42.5R cement (European Standard EN-197/1), commercial hydrated lime and coal fly ash supplied by the ENEL (Italian Electricity Board) power plant located in Brindisi (Italy). The granules manufacture has been carried out by means of a granulator equipped with a rotating and tilting plate (Fig. 1). The rotating speed and the tilting angle can be adjusted between wide limits. In the experiment, the settings were 40 and 60 rpm for the rotating speed and 50° for the tilting angle.

Figure 1 Granulation equipment

The granules manufacture made use of the following technique. A weighted amount of solid mix was slowly and continuously poured into the granulator plate. Simultaneously, water was fed through a nozzle at a proper rate and, in the initial granulation phase, the rotating speed was adjusted at 40 rpm to favor the formation of the granules nuclei. This initial phase gives granules with a very wide size distribution. A further granulation phase followed in which neither solid mix nor water were added and the rotating speed was adjusted at 60 rpm. This makes smaller granules coalesce and favors granules compacting by the expulsion of part of the water employed in the initial phase. The whole manufacture process lasts about 20 minutes and the final product is composed of compacted granules with most of them in the range 4-18 mm. The amounts of solid mix and water employed, their feed rates to the granulator plate and the rotating speeds in the two granulation phases are the results of specific process optimization.

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The granules obtained as described were cured 12 hours in a climatic chamber where temperature and relative humidity were kept at 50°C and 95%, respectively. This curing phase favors granules hardening, necessary for successive handling. Finally, the granules were submitted to a 14-day curing at room temperature and humidity. It was checked that further curing in these conditions did not improve the technological properties of the granules. In all the granules preparations 800 g of solid mixes were used, whose compositions are reported in Table 4. All the systems listed in this table were submitted to a second granulation step in which a 50/50 cement/coal fly ash binder was used in amount equal to 40% of granules weight. In the following, these systems are distinguished by placing the + sign at the end of each label. The scope of the two-step granulation was to encapsulate the primary granulation products into an outer pure binder layer able to improve the technological properties and the leaching behavior of the final products. The granules obtained in the different experimental conditions were submitted to technological characterization through the determination of some selected physicomechanical properties. The granules size distribution was determined by sieving according to UNI EN 933-1 standard. The granules density was found to vary with size. Then, it was determined on two different size fractions: 4-12 mm and 12-18 mm. The technique was as follows. Each specimen was soaked into water at 20±2°C and then superficially wiped with a moist cloth. This was repeated every 24 hours until constant weight was reached. The water saturated granules were used for the determination of the specimen volume by means of water displacement. The mass of the same specimen was determined after drying at 105±5°C. Following this procedure, the granules apparent density was obtained. Table 4. Granules composition, wt%

System

R70C S70C R70L S70L R60LA S60LA R50LA S50LA

Ash origin Rotary Stoker furnace furnace

70 70 60 50 -

70 70 60 50

Binder type Cement

Lime

Coal fly ash

30 30 -

30 30 15 15 30 30

25 25 20 20

Water/solid ratio

0.25 0.41 0.25 0.36 0.32 0.39 0.35 0.40

The water absorption capacity (WAC) was determined as described in [30]. The water saturated granules (see the above paragraph) were dried at 40±2°C until constant weight was reached. Then, WAC was determined by means of the following relationship: WAC = 100(MW-MD)/MD where MW is the water saturated granules mass and MD is the 40±2°C dried granules mass.

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The Los Angeles coefficient is a measure of aggregate degradation resulting from a combination of actions including abrasion (attrition), impact and grinding in a rotating steel drum containing a specified number of steel spheres according to UNI EN 1097-2 standard (ASTM C131). The specimen is washed and oven dried at 110±5°C until constant weight is reached. Then, it is loaded into the rotating drum together with the specified number of spheres (depending on the charge weight). After 500 drum revolutions at 30-33 rpm, the specimen is discharged and sieved through a 1.7 mm sieve (No. 8 of UNI 2331/2332 sieve series or 12 mesh of ASTM E 11-70 series). The Los Angeles coefficient is exactly the difference between the original charge weight and the recovered one after sieving expressed in terms of percentage of the original weight. The result is rounded to 1%. The measurement of the granules compressive (crushing) strength was carried out according to UNI 7549/7 standard by means of a 3000 kN Controls MC60 press. Concrete was prepared by mixing 0.11 m3 of cement (density 3140 kg/m3), 0.17 m3 of water, 0.31 m3 of fine natural aggregate (density 2200 kg/m3) and 0.41 m3 of artificial aggregate in replacement of the coarse fraction. Concrete cubic specimens (15 cm in size) were employed for the measurement of compressive strength, according to UNI 6132 standard. The equipment was the same press referred to above. The concrete dynamic modulus of elasticity was determined using cylindrical specimens (15 cm in diameter and 30 cm in height) by means of ultrasonic pulse measurement. According to Rilem NDT 1 standard, this method links the elasticity modulus to the velocity with which an ultrasonic pulse passes through the material under investigation. A Matest apparatus was used for this measurement. In both cases of concrete compressive strength and elasticity modulus measurements, three specimens were used for each data point after 28 days of water curing.

RESULTS AND DISCUSSION Table 5 shows the results of density and WAC measurements separately carried out on the two different size fractions of all the granules tested. As far as the density is concerned, it is clearly seen that this property increases as the ash content increases. Furthermore, the density is greater for the smaller size fraction. This is due to the fact that, during the final compacting phase of granulation, water is more easily expelled in the case of smaller granules. The ash origin (from stoker or rotary furnace incinerator) has no significant effect on granules density, despite the greater water requirement in the granules manufacture starting from stoker furnace incinerator ash. Finally, analyzing the results for the systems containing 70% ash, it is possible to draw the conclusion that higher density is obtained when cement is used in the granules manufacture instead of lime. The values of density found for the granules manufactured in this study are such that they can be classified as lightweight aggregate. In fact, Lytag, a commercially available lightweight aggregate, was shown to have density in the range 1370-1490 kg/m3 [19], while typical natural aggregate density ranges from 2400 to 2800 kg/m3. The majority of our density data are lower than the Lytag lower limit of 1370 kg/m3, and only in a few cases

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values greater than 1490 kg/m3 have been found. Then, the proposed granulation technique proves to be suitable for the manufacture of lightweight artificial aggregate. Table 5. Density and water absorption capacity (WAC) of granules

System

R70C R70C+ S70C S70C+ R70L R70L+ S70L S70L+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Density, kg/m3 Size fraction, mm 4-12 12-18

1585 1596 1596 1612 1431 1445 1458 1452 1433 1428 1406 1442 1365 1368 1359 1375

1136 1196 1203 1226 1011 1037 1050 1081 1027 1051 1023 1101 976 995 989 1062

WAC, wt% Size fraction, mm 4-12 12-18

11.22 9.80 9.62 8.25 13.86 11.95 11.67 10.28 10.62 9.18 8.95 7.43 10.62 9.73 8.90 7.34

13.54 11.73 12.01 10.21 15.46 13.65 14.31 12.11 12.81 10.95 11.08 9.41 12.23 10.71 10.00 9.70

The values of WAC are clearly affected by the size of the fraction under consideration. In fact, higher values are found for the 12-18 mm fraction. This result is in agreement with those relative to density, inasmuch as less dense (more porous) granules are obviously able to absorb water to a greater extent. Another observation can be drawn once the results for the systems containing 70% ash are considered. It is seen that lime-based systems have greater WAC than those cement-based, again in agreement with density data. When compared to the commercial lightweight aggregate referred to above, the values of WAC found for the granules tested in this study lay within a range whose limits are lower. In fact, WAC ranges between 10 and 16% for Lytag aggregate [19], while, for the granules manufactured in this study, the range is 8.9-15.5% for one-step granulation and 7.3-13.7% in the case of two-step granulation. Table 6 shows the results of technological properties measurement, specifically compressive (crushing) strength and Los Angeles coefficient. It is seen that compressive strength is lower for the larger size fraction, in agreement with density data. Moreover, with a few exceptions, compressive strength is higher when the binder content is higher, as can be obviously expected. The effect of binder type can be observed once the data for the systems at constant ash content (70%) are taken into account. These data show that the use of cement offers advantages over lime. Finally, the data of Table 6 show that there is a clear and definite effect of ash type, as the one coming from the stoker furnace incinerator gives better compressive strength results.

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R. Cioffi, F. Colangelo, F. Montagnaro and L. Santoro Table 6. Compression (crushing) strength and Los Angeles coefficient of granules

System

R70C R70C+ S70C S70C+ R70L R70L+ S70L S70L+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Compressive strength, MPa Size fraction, mm 4-12 12-18

3.76 5.28 5.10 6.60 2.33 3.22 3.10 4.01 3.21 4.81 4.92 5.86 3.05 4.61 4.65 5.83

2.21 3.65 3.50 4.80 1.42 2.28 2.10 2.78 1.88 3.32 3.32 4.53 1.83 3.36 3.12 4.29

Los Angeles coefficient, wt% Size fraction, mm 12-18

48 44 46 42 59 56 57 53 48 43 44 41 48 43 44 40

In many cases the observed values of compressive strength are such that the granules tested in this study are suitable for use as lightweight aggregate in civil engineering applications. In fact, Lytag commercial lightweight aggregate has compressive strength in the range 4.8-9.2 MPa [19]. The results of Los Angeles coefficient measurement are presented in Table 6 only for the 12-18 mm size fraction and show no definite trend when the ash content is changed. The only clearly observable effects are those of binder and ash types. In fact, this coefficient is higher for lime-based granules than for cement-based ones, and is slightly lower when stoker furnace incinerator ash is used for the manufacture of the granules. Typical natural siliceous aggregate has Los Angeles coefficient of about 20% [14]. On the other hand, the values of this coefficient for artificial aggregates coming from crushed bricks and fired fly ash-clay mix are higher, reaching 30% [14]. The values of the Los Angeles coefficient found for the aggregates under investigation (Table 6) are still higher, but, according to the Italian regulation [31], no compliance minimum value is required for ordinary concrete manufacture. Table 7 shows the results of the leaching test carried out on the size fraction 12-18 mm of the granules manufactured starting from the rotary furnace incinerator ash. The size fraction 4-12 mm was excluded from this test because the granules were found of better physical properties (higher density, lower porosity) in this size fraction. Moreover, all the samples obtained from stoker furnace incinerator ash were not tested for leaching behavior. The reason for this is that granules based on this ash proved to have better physical and technological properties in relation to civil engineering applications. In addition, as can be seen in Table 1, stoker furnace incinerator ash is poorer of heavy metals of environmental concern than rotary furnace incinerator ash.

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Table 7. Leaching behavior of granules

System

R70C R70C+ R70L R70L+ R60LA R60LA+ R50LA R50LA+

Cd, µg/L Limit=5 Time, days 16 28 56

3 1 6 1 3 1 3 1

3 1 7 1 3 1 4 1

4 1 8 1 4 1 4 1

Zn, mg/L Limit=3 Time, days 16 28 56

2.13 0.67 3.62 0.92 2.31 0.58 2.21 0.61

2.49 0.79 4.31 1.02 2.38 0.73 2.48 0.70

2.71 0.91 4.87 1.09 2.93 0.78 2.83 0.86

Pb, µg/L Limit=50 Time, days 16 28 56

Cu, µg/L Limit=50 Time, days 16 28 56

12 3 47 3 12 3 13 3

27 10 41 13 24 9 23 10

15 4 54 3 17 4 14 3

21 4 68 4 19 4 20 4

32 12 59 16 26 9 28 13

38 15 68 19 29 11 31 15

The metal release values of Table 7 are cumulative and relative to three times: 16, 28 and 56 days. According to Italian regulation, only the cumulative release value after 16 days is to be taken into account for comparison with the limit fixed for each metal. The compliance leaching test employed for the granules was extended to 28 and 56 days to have a better understanding of the long term leaching behavior of the granules. As the leaching test is of compliance type, the first observation on the data of Table 7 must be related to the cases in which the limits are exceeded. This only happens for Cd and Zn in system R70L. In all the other cases the cumulative amounts of metals released after 16 days are below the relative limits. As expected, the release is much lower in the case of granules manufactured via the two-step granulation. Metal release is also affected by the type of binder. In fact, cement-based granules containing 70% ash behave better than the corresponding lime-based ones. This is quite an expected result, as the physico-mechanical properties of the granules based on lime alone as binder were found of the worst rank. The effect of ash content on leaching behavior does not seem significant, at least in the composition range investigated. A final consideration can be made with regard to release at times longer than 16 days (28 and 56 days). It is seen that in all the cases investigated the release at these longer times increases over that at 16 days but to a limited extent, and this is a very positive result in view of long-term behavior in civil applications. Table 8 shows some selected properties of concrete blocks incorporating different types of granules. Lime-based granules were not used for the manufacture of the concrete blocks due to their poor technological properties. According to Italian rules, concrete blocks that give at least 95% of compressive strength determinations greater than X MPa for cubic samples 15 cm in size or Y MPa for cylindrical samples 10 cm in diameter and 15 cm in height are classified as belonging to class CX/Y [32]. Nine classes exist starting from C12/15 to C50/60. The data of compressive strength reported in Table 8 show that all the granules tested are suitable for the manufacture of concrete blocks for civil engineering applications. Actually, blocks of the four classes C16/20, C20/25, C25/30 and C30/35 could well be manufactured. Table 8 also shows that blocks manufactured starting from granules obtained via two-step granulation have better compressive strength values, while no simple relationship exists

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between ash content in the granules and concrete blocks compressive strength. On the other hand, concrete blocks density is seen to decrease as the ash content in the granules decreases. Furthermore, any of the properties in Table 8 (density, compressive strength and elasticity modulus) increase when the concrete blocks incorporate the granules produced via two-step granulation. Table 8. Properties of concrete incorporating the granules Granules

R70C R70C+ S70C S70C+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Density, kg/m3

Compressive strength, MPa

Elasticity modulus, GPa

1908 1932 1949 1963 1742 1745 1734 1749 1665 1672 1659 1682

20.06 27.21 26.35 34.00 18.06 25.86 26.13 30.35 17.15 24.72 25.68 31.67

24.76 26.34 26.45 28.00 24.79 26.23 26.18 27.34 23.64 25.63 26.08 27.53

As far as the modulus of elasticity is concerned, it should be observed that typical values for concrete blocks containing natural aggregates range from 25 to 50 GPa [33]. Then, the measurements carried out on the blocks under investigation show values near to the lower limit of the range referred to above. This is a favorable property as low values of the modulus of elasticity are preferred for mitigating cracking due to shrinkage.

CONCLUSIONS First of all this work has proved that ash from municipal, hospital and industrial solid wastes incinerator can be successfully employed up to 70% content in the production of artificial aggregate in the form of granules. Different binders can be used for the production of the granules, but only cement and coal fly ash/lime give satisfactory technological properties. Lime alone proved to be unsuitable as granules binder. Of the two ash samples employed in this study, from stoker and rotary furnace incinerators, the former was able to give granules of better technological properties. In the majority of the cases tested, the release of heavy metals was below the limits fixed by Italian law for civil engineering applications. Exceptions to this have only been observed when lime alone is used as a binder for the production of the granules. All the relevant granules properties, mainly compressive strength and leaching behavior, improve when the granules are produced via a two-step granulation process. This was an

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expected result as the second granulation step produces an encapsulating pure binder outer layer. Finally, the granules tested in this study have proved to be suitable for the manufacture of concrete blocks. Depending on process variables (type of binder, granules composition, type of granulation) granules can be produced of physico-mechanical properties good enough to allow the manufacture of concrete blocks of middle range performance.

REFERENCES [1] [2]

[3]

[4]

[5]

[6] [7] [8]

[9] [10]

[11] [12]

[13]

Collivignarelli C. and Sorlini S., Reuse of municipal solid wastes incineration fly ashes in concrete mixtures, Waste Management 22 (2002) 909-912. Smith J.D., Fang H. and Peaslee K.D., Characterization and recycling of spent refractory wastes from metal manufacturers in Missouri, Resources, Conservation and Recycling 25 (1999) 151-169. Chang N.B., Wang H.P., Huang W.L. and Lin K.S., The assessment of reuse potential for municipal solid waste and refuse-derived fuel incineration ashes, Resources, Conservation and Recycling 25 (1999) 255-270. Montepara A. and Tebaldi G., Use of crushed waste aggregates for DBM road bases, Waste Management Series, Volume 1, Waste Materials in Construction – Wascon 2000, Pergamon Press, The Netherlands (2000). Van der Sloot H.A., Kosson D.S. and Hjelmar O., Characteristics, treatment and utilization of residues from municipal waste incineration, Waste Management 21 (2001) 753-765. Ahmadi B. and Al-Khaja W., Utilization of paper waste sludge in the building construction industry, Resources, Conservation and Recycling 32 (2001) 105-113. Hill A.R., Dawson A.R. and Mundy M., Utilisation of aggregate materials in road construction and bulk fill, Resources, Conservation and Recycling 32 (2001) 305-320. Huang W.L., Lin D.H., Chang N.B. and Lin K.S., Recycling of construction and demilition waste via a mechanical sorting process, Resources, Conservation and Recycling 37 (2002) 23-37. Forteza R., Far M., Seguí C. and Cerdá V., Characterization of bottom ash in municipal solid waste incinerators for its use in road base, Waste Management 24 (2004) 899-909. Cho Y.H. and Yeo S.H., Application of recycled waste aggregate to lean concrete subbase in highway pavement, Canadian Journal of Civil Engineering 31 (2004) 11011108. Topcu I.B. and Sengel S., Properties of concretes produced with waste aggregate, Cement and Concrete Research 34 (2004) 1307-1312. Sani D., Moriconi G., Fava G. and Corinaldesi V., Leaching and mechanical behaviour of concrete manufactured with recycled aggregates, Waste Management 25 (2005) 177182. Senthamarai R.M. and Manoharan P.D., Concrete with ceramic waste aggregate, Cement and Concrete Composites 27 (2005) 910-913.

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[14] Zakaria M. and Cabrera J.G., Performance and durability of concrete made with demolition waste and artificial fly ash-clay aggregates, Waste Management 16 (1996) 151-158. [15] Van der Sloot H.A., Hoede D., Cresswell D.J.F. and Barton J.R., Leaching behaviour of synthetic aggregates, Waste Management 21 (2001) 221-228. [16] Wainwright P.J. and Cresswell D.J.F., Synthetic aggregates from combustion ashes using an innovative rotary kiln, Waste Management 21 (2001) 241-246. [17] Wang K.S., Sun C.J. and Yeh C.C., The thermotreatment of MSW incinerator fly ash for use as an aggregate: a study of the characteristics of size-fractioning, Resources, Conservation and Recycling 35 (2002) 177-190. [18] Pioro L.S. and Pioro I.L., Reprocessing of metallurgical slag into materials for the building industry, Waste Management 24 (2004) 371-379. [19] Cheeseman C.R., Makinde A. and Bethanis S., Properties of lightweight aggregate produced by rapid sintering of incinerator bottom ash, Resources, Conservation and Recycling 43 (2005) 147-162. [20] Cheeseman C.R. and Virdi G.S., Properties and microstructure of lightweight aggregate produced from sintered sewage sludge ash, Resources, Conservation and Recycling 45 (2005) 18-30. [21] Conner J.R., Chemical fixation and solidification of hazardous wastes, Van Nostrand Reinhold, New York, NY, USA (1990). [22] Spence R.D., Chemistry and microstructure of solidified waste forms, Lewis Publishers, Boca Raton, FL, USA (1993). [23] Means J.L., Smith L.A., Nehring K.W., Brauning S.E., Gavaskar A.R., Sass B.M., Wiles C.C. and Mashni C.I., The application of solidification/stabilization to waste materials, Lewis Publishers, Boca Raton, FL, USA (1995). [24] Spence R.D. and Shi C., Stabilization and solidification of hazardous radioactive and mixed wastes, CRC Press, Boca Raton, FL, USA (2005). [25] Beretka J., Cioffi R., Santoro L., and Valenti G.L., Cementitious mixtures containing industrial process wastes suitable for the manufacture of preformed building materials, Journal of Chemical Technology and Biotechnology 59 (1994) 243-247. [26] Cioffi R., Maffucci L., Santoro L. and Glasser F.P., Stabilization of chloro-organics using organophilic bentonite in a cement-blast furnace slag matrix, Waste Management 21 (2001) 651-660. [27] Calvanese G., Cioffi R. and Santoro L., Cement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent, Environmental Technology 23 (2002) 1051-1062. [28] Italian Standard UNI 10802, Liquid, granular, semisolid wastes and sludges – Manual sampling, leaching and leachate analysis, Milano, Italy (1999). [29] Act of Italian Environment Ministry (DM), 5 February 1998. [30] Ramachandran V.S. and Beaudoin J.J., Handbook of Analytical Techniques in Concrete Science and Technology, Noyes Publications/Andrew Publishing, Norwich, New York, USA (2001). [31] Act of Italian Republic President (DPR), 21 April 1993. [32] Italian Standard UNI 9858, Concrete: performance, production, utilization and compliance criteria, Milano, Italy (1991). [33] Collepardi M., Il Nuovo Calcestruzzo, ENCO, Milano, Italy (2003).

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 235-245 © 2006 Nova Science Publishers, Inc.

Chapter 8

THE CHEMICAL PROPERTIES OF MUNICIPAL SOLID WASTE INCINERATOR ASHES AND THE EFFECTS OF THEIR UTILIZATION AS LANDFILL COVER ON LANDFILL BIOSTABILIZATION Huang-Mu Lo∗a, Min-Hsin Liua, Chao-Yang Linb, Wen-Fung Liuc, Tzu-Yi Paia, Chun-Hsiung Hungb, Pin-Hung Chengd, Yuan-Lung Liaoa, Tsu-Ying Fua and Chao-Chan Yanga a

Chaoyang University of Technology, Taiwan, R. O. C. b National Chung Hsing University, Taiwan, R. O. C. c Feng Chia University, Taiwan, R. O. C. d Taipei University of Science and Technology, Taiwan, R. O. C.

ABSTRACT This article investigated the properties of municipal solid waste incinerator (MSWI) ashes and the effects of their addition on the municipal solid waste (MSW) anaerobic digestion as co-disposed or co-digested with MSW in landfill or digester. Five anaerobic bioreactors with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers were arranged each with 6.5 liter of MSW and anaerobic seeded sludge mixture covered by 2.5 liter of MSW and anaerobic seeded sludge mixture blended with the designed ashes added ratios as well as the control bioreactors without ashes addition. The synthetic MSW used in this experiment was typical of organic fraction of MSW and was comprised of newspaper, food waste, office paper and hay etc. MSWI ashes were obtained from a mass burning incinerator in central Taiwan. Also, the seeded anaerobic sludge was taken from a municipal wastewater treatment in central ∗

Corresponding author. Tel.: +886-4-23323000 ext 4469; fax: +886-4-23742365. E-mail address: [email protected] (Huang-Mu Lo)

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Huang-Mu Lo, Min-Hsin Liu, Chao-Yang Lin et al. Taiwan. As the experiment was proceeded with, the leachate of 100 mL was recirculated per day and another more 100 mL one was collected and filtered for parameters analysis such as pH, conductivity, alkalinity and chemical oxygen demand (COD) etc. In addition, the gas production rate was recorded every day to measure the bacterial activity in the MSW biodegradation. From the results, it showed that 10 and 20 g l-1 fly ash added (g ashes addition per liter MSW ratios) bioreactors and 100 g l-1 bottom ash added bioreactors were found to enhance the gas production rate and the soluble concentration of alkali metals such as Ca, Mg, K, and Na as compared to the control one. The six soluble heavy metals of Cd, Cr, Cu, Pb, Ni and Zn in leachate were also found to be under inhibitory concentration for anaerobic digestion. Other trace metals such as Co and Mo etc were assumed to serve as the stimulatory micronutrients rather than to exert inhibitory effects on the microorganisms in the MSW anaerobic digestion.

Keywords: Anaerobic digestion, Landfill, MSW, MSWI ashes

INTRODUCTION Municipal solid waste (MSW) incinerator (MSWI) has been practiced in the MSW treatment as important as landfill, composting and resource recovery and recycling. This is because that the likely landfill site is getting more difficult to find for the MSW disposal particularly occurred in the dense population and lesser appropriate land for landfill in Taiwan. MSWI can take the advantage of MSW weight or volume reduction and the recovery of steam and electricity. However, the residues such as bottom ash and fly ash generated were still the primary environmental concern. Thus, they need to be carefully treated to prevent the potential secondary pollution. Particularly, the released metals, ions and other compounds if not properly treated might be toxic to the human health and ecological environment when utilized in different purposes. Therefore, MSWI residues treatment and disposal has become another environmental task in MSW treatment. MSWI residues have been utilized as aggregate, backfill, soil amendment and solidified for permanent landfill storage as well (Bertolini et al., 2004; Deschamps, 1998; Hjelmar, 1996). In addition, MSWI bottom ash has been practiced as landfill cover, however, the baseline information and landfill mechanisms were not fully clear. Only few research investigated the bottom ash co-digested with MSW in the semi-batch anaerobic bioreactor (Lo, 2005). This study showed that bottom ash addition could provide the alkalinity suitable for the anaerobic digestion thus enhancing the gas production rate. Another investigation also presented that NaHCO3 could provide alkalinity and facilitate the MSW anaerobic digestion process (Ağdağ and Sponza, 2005). As regard to MSWI fly ash, it is thought that using fly ash as landfill cover is an aggressive challenge for the landfill practice. It is further noted that fly ash has the potential to release the heavy metals which is considered to be hazardous to the soil and ground water if disposed improperly or leaked from the faulty geo-membrane liner in the bottom of landfill. The soil and ground water contamination by the release of MSWI ashes in landfill might have the potential to cause detrimental effects on human health and ecological environment. Therefore, using fly ash as landfill cover might be an aggressive challenge needing further theoretical and experimental investigation. In addition, it is noted that MSW landfill needs a long term period to obtain the MSW biostabilization. Thus, anaerobic landfill bioreactors

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were employed to conduct the experiment of MSW and MSWI ashes co-disposal to obtain the results in a short term. Particularly, the pH, alkalinity, COD, metals and gas production in the bioreactors were measured to assess the MSW biostabilization in landfill bioreactor simulating the real landfill site.

MATERIALS AND METHODS MSWI Ashes The MSWI bottom ash and fly ash required for the bioreactor experiment were derived from a mass burning MSWI in central Taiwan (Figure 1). Generally, bottom ash was obtained from the incinerator stoker which is the major part for the MSW incineration as well as the siftings leaked from the stoker. Fly ash was derived from the air pollution control device (APCD) such as semi-scrubber and bag filter. Fly ash has been measured to have smaller particle size as compared to that of the bottom ash by sieve analysis. Thus, it is expected that fly ash particle contains higher specific surface than that of bottom ash leading in the potential higher release of metals, ions and compounds. These released metals, ions and compounds might further influence the different utilization purposes. Particularly, the released heavy metals were reported to have the potential to cause the human health and ecological environment. The metal total content in MSWI ashes was characterized as Figure 2.

10 11

22 20

2

5 15

17

6 1

13

4

3

18

12 16

8

14 9

Refuse flow Air flow

7

19

Residue ash flow Steam flow

21 Fly ash flow Gas flow

1.Refuse unloading area 2.C rane operation room 3.Pit 4.Secondary air blower 5.Crane 6.Hopper 7.Air compressor room 8.Ash crane 9.Ash pit 10.Tap water 11.Boiler 12.Grate 13.Ventilation room 14.Ash conveyor 15.Economizer 16.Fly ash conveyer 17.Semi-dry scrubber 18.Central control room 19.Transformer room 20.Bagfilter 21.Induce fan 22.Stack

Figure 1. The treatment process of mass burning MSW incinerator

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Office paper (30%) Newspaper (30%)

Food waste (5%)

Shredder

Hay (35%)

Water (16 L)

Moisture adjustment with blender (TS 6%)

Amount of designed Ashes addition

Biogas production

Anaerobic bioreactor

Leachate or digestate filtration

Parameters analysis Performance assessment

Figure 2. Schematic diagram showing the preparation of feedstock, its component composition, and bioreactor outputs and analysis

MSW In order to reduce the interference of potential hazardous materials in MSW, synthetic MSW was prepared artificially in the laboratory. The MSW was comprised of newspaper (30%), office paper (35%), food waste (5%) as potato and hay (30%) etc. These constituents were typical of major organic fraction of MSW. With the measurement by elemental analyzer, the chemical composition consisting of C, H, O, N and others were about 46 %, 6 %, 41 %, 1.4 % and 5.6 % respectively. These constituents contained typical organic fraction of MSW and were easily to be biodegraded by microorganisms. For the convenience of microbial attack in the decomposition process, synthetic MSW was shredded by a shredder to pieces of less than 5 mm. Then, it was blended with distilled water to make a total solid (TS) of 6%. Although this percent of TS was lower than that of real landfill MSW, the carbon content is near the same. In addition, this investigation focused on the effects of MSWI ashes co-disposed with MSW to examine the metals and ions release on the MSW decomposition and their possibility of utilization as landfill cover. The MSW preparation procedure and metal total content in MSW were listed as Figure 2 and Figure 3.

Anaerobic Seeded Sludge To ensure the MSW biodegradation occurred without retardation, anaerobic seeded sludge was taken from a municipal waste water plant in central Taiwan. This plant collects the municipal waste water from Taichng city. The anaerobic sludge showed efficient bacterial

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239

activity that was beneficial for the startup and biodegradation of MSW in the anaerobic bioreactor. The metal content of anaerobic seeded sludge was indicated in Figure 3. 300

Sludge

MSW

Fly ash

Bottom ash

Total content, mgg

-1

250

1A

200 150 100 50 0 Ca

K

Mg

Na

Fe

P

S

Metal

4

Sludge

MSW

Fly ash

Total content, mgg -1

3.5

Bottom ash

1B

3 2.5 2 1.5 1 0.5 0 Ag Al B BaCd Co Cr Cu Hf In MnMo Ni Pb Sb Si Sn Ta Ti Tl V W Zn Zr Metal

Figure 3. The selected metal content in sludge, MSW, fly ash and bottom ash

Anaerobic Bioreactor In order to obtain the effects of MSWI ashes co-disposed with MSW in a short term, five anaerobic bioreactors (Figure 4) with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers of co-disposal simulating the landfill site operation were arranged. Two of them were set up for bottom ash co-disposal with MSW and the other two were for fly ash co-disposal with MSW. The fifth one was used to compare the results without any ashes addition. The designed added ratios of bottom ash were 100 and 200 g l-1 (100 and 200 g addition per liter MSW) and of fly ash were 10 and 20 g l-1 respectively. In these bioreactors, it consisted of 22 liter MSW and 12 liter of anaerobic sludge accompanying by the designed ashes addition. Each layer within the four ones of anaerobic bioreactor contained 6.5 liter of MSW and seeded sludge mixture and was covered with 2 liter

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of MSW and seeded sludge mixture blended with the designed MSWI ashes addition as previously stated. The 100 ml leachate at the bottom of the bioreactor was recirculated each day. In addition, another more 100 ml leachate was collected and filtered for parameters analysis such as pH, alkalinity, chemical oxygen demand (COD), total solid (TS), volatile solid (VS) and metals daily or weekly. Gas production was also measured with gas collector daily. The measured parameters and gas production rate can be used to assess the performance of the anaerobic bioreactors.

Gas meter

pH, COD, TS, VS, Alkalinity, metals analyses etc

Figure 4. The schematic diagram of anaerobic bioreactor in the experiment

Biogas 4 Methanogenesis -Methanosarcina -Methanothrix -Methanobacterium 3 Acetogenesis -Syntrophobacter -Syntrophomonas -Desulfovibro

Acetate

H2

CO2

Organic acids

Acetate

Alcohol

2 Acidogenesis -Acidifying bacteria -H2 producing acetogens 1 Hydrolysis -Clostridium -Eubacterium -Peptococcus

Breakdown products (amino acids, sugars, large carboxylic acids)

Substrates (carbohydrate, fat, protein, lipid)

Figure 5. Biochemical process in anaerobic digestion (Dichtl, 1997; House et al., 1997; Bhatti et al., 1996)

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pH was measured by a pH meter. Alkalinity and COD were measured with titration methods. TS and VS were analyzed with the oven at 105 and 600°C respectively. All these analysis methods followed the standard methods for the examination of water and wastewater (AWWA, 1995). Microorganisms play an important role on MSW anaerobic digestion process (Figure 5). Molecular biotechnology of FISH was used to characterize the selected methanogens such as Methanobacteriales, Methanococcales, Methanosarcinales and Methanomicrobiales and the target probes were MB310, MC1109, MSMX860 and MG1200 (Raskin et al., 1994) respectively. Methanogens detection could provide an indication of methanogenesis extent of MSW anaerobic digestion as the MSWI ashes were added.

RESULTS AND DISCUSSION Parameters Analysis From the experimental results, it showed that pH trends of bioreactors in leachate (Figure 6A) have shown lower values at the beginning in the five bioreactors. Thereafter, they reached to the steady values of about pH 6.2-7.5. The pHs in the bottom ash added bioreactors were found higher than that in fly ash added and control ones specifically found in the 200 g l-1 bottom ash added bioreactors with the pHs higher than 7.5 after about month six. Further, the lower pHs below 6 found in the five bioreactors at the beginning except first week was thought that large amount of VA was produced in the first stage of MSW hydrolysis leading to the higher volatile acids and lower pHs. However, the pHs returned to about pH 6.2-7.5 soon possibly due to the alkali metal hydroxides and carbonates release which could provide the buffer alkalinity and neutralize VA as a function of pH. This range of near neutral pHs were thought to be suitable for the anaerobic digestion (Lo, 2005; Parkin and Owen,1986). Conductivity was found higher in the ash added bioreactors than the control one (Figure 6B). Conductivity in the 20 and 10 g l-1 fly ash added bioreactor was found to be about three times and two times that of control one respectively. This is because that higher fly ash addition could release higher different kinds of ions such as metals and chlorides etc resulting to a higher conductivity. As regarding to alkalinity, the alkalinity concentrations in the five bioreactors had the same trends between 500 and 3500 mg l-1 and were found to be in the suitable range for the anaerobic digestion as described by Parkin and Owen (1986) and can be seen in Figure 6C. VA in the five bioreactors was found to decrease except that found to increase in the 20 g -1 l ash added bioreactor between week two and week five (Figure 6D). From the third month on, the VA started to increase slightly. VA found higher in the first month was thought that the MSW was hydrolyzed in the first digestion stage resulting to a large amount of VA production such as acetate, propionate, butyrate, valerate etc. VA concentrations were then maintained in a steady state within the five bioreactors from month two to about month three. In the mean time, VA was converted to the methane and carbon dioxide by methanogenic bacteria as the gas production rate was found higher in this period. In addition, the VA in the MSWI ashes added bioreactors was found slightly higher than that in the control bioreactors at the beginning. From the fourth month on, the VA in the five bioreactors was found to increase slightly. This phenomenon indicated that the methanogenic activity began to

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decrease possibly due to the MSW anaerobic digestion completion and the lesser MSW substrate left to be utilized. 25 Conductivity, ms/cm

6A 8.5 pH

7.5 6.5 5.5 4.5 0

50

100

150

200

5

0

3000 2000 1000 0 40

50

-1

Volatile acids, mgl

-1

Alkalinity, mgl

6C

4000

20 30 Week

10

50

100

150

200

250

Day

5000

10

15

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2000 1500 1000 500 0 0

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Figure 6. The trend of pH, conductivity, alkalinity and volatile acids in leachate of MSW anaerobic digestion by five different addition ratios of MSWI fly ash added, bottom ash added and the control bioreactors (◇: control bioreactor without ash addition; □: 10 g l-1 fly ash added bioreactor; △: 20 g l1 fly ash added bioreactor; ＊: 100 g l-1 bottom ash added bioreactor; ●: 200 g l-1 bottom ash added bioreactor).

GAS PRODUCTION RATE AND METALS RELEASE Released metals have been found to influence the MSW anaerobic digestion. The gas production rate in the MSWI ashes added bioreactors was found higher as compared to that in the control one (Figure 7). Higher gas production rate in the ash added bioreactors was thought that the release of alkali metals such as Ca, Mg, K and Na and the associated OH-1 and CO3-2 have provided the pH buffer in neutral band which facilitated the anaerobic digestion. In addition, six heavy metals of Cd (0-0.001 mgl-1), Cr (0-0.014 mgl-1), Cu (0-0.05 mgl-1), Pb (0-1.75 mgl-1), Ni (0-0.025 mgl-1) and Zn (0-0.05 mgl-1) in leachate were measured to be under inhibitory soluble concentration. It is further noted that trace metals such as Co, W, Ni etc might serve as the micro nutrients (Takashima and Speece, 1990; Kayhanian and Rich,1995; Paulo et al., 2004; Fish, 1999; Zandvoort et al., 2004). Thus, the gas production rate was facilitated and the MSW digestion was accelerated. Moreover, microorganisms of selected methanogens were found higher in the period of higher gas production rate within the ashes added bioreactors. Microorganisms seemed to be stimulated by the suitable metals release which was beneficial to the anaerobic digestion. Therefore, MSW anaerobic digestion

The Chemical Properties of Municipal Solid Waste Incinerator Ashes …

243

efficiency was enhanced and the gas production rate and MSW biostabilisation were increased. It was further noted that the highest gas production rate in all bioreactors seemed to take place about on day 30. The gas production rate of the ashes added bioreactors on the peak was found to be about 9000 ml per day nearly two times that of 4500 ml per day found in the control one. The gas production rate in the bottom ash added bioreactor decreased quickly from the peak to zero on day 42. Similarly, the gas production rate in the control bioreactor also decreased quickly from the peak to nearly zero on about day 90. The gas production rate in the 20 g l-1 ash added bioreactor appeared to have stayed at a constant rate of about 6500 ml lasting between day 38 and day 51. As a result, the gas production accumulation in the decomposition period of all the bioreactors ranked in the order of 20 g l-1 fly ash added bioreactor > control bioreactor > 10 g l-1 fly ash added bioreactor > 100 g l-1 bottom ash added bioreactor. The lowest gas accumulation happened to the 100 g l-1 bottom ash bioreactor was thought to be the higher amount and quicker release of metals hydroxides, carbonates and phosphates. These released OH-1, CO3-2 and PO4-3 etc were considered to give alkalinity buffer and was neutralized by the quick production and large amount of volatile acids generated in the first hydrolysis of MSW anaerobic digestion.

Gas production, mL

10000 8000 6000 4000 2000 0 0

50

100

150

200

Day Figure 7. The gas production rate of MSW anaerobic digestion by three different addition ratios of MSWI fly ash in the ash added and the control bioreactors (○: 100 g l-1 bottom ash added bioreactor; □: 10 g l-1 fly ash added bioreactor; △: 20 g l-1 fly ash added bioreactor; : control bioreactor without fly ash addition).

EVALUATION OF ANAEROBIC BIOREACTOR PERFORMANCE From this investigation, the designed ratios of MSWI ashes added bioreactors were found to be able to enhance the gas production rate as compared to the control one. This phenomenon was mainly attributed to the suitable pH, alkalinity and suitable released metals such as alkali metals, trace metals and heavy metals and associated hydroxides and carbonates. Alkali metal compounds and their dissolution of OH-1 and CO3-2 were thought to

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provide the suitable alkalinity and pH offer. In addition, alkali metals were found to be below inhibitory concentration (Parkin and Owen, 1986) and the trace compounds such as dioxin and PAH seemed not exert detrimental effects on bacterial activity and the MSW anaerobic digestion. Similarly, the released heavy metals were also measured to be under the threshold concentration that might be inhibitory on the effects of MSW anaerobic digestion. Further, trace metals were analyzed to be suitable for serving as micronutrients required for the anaerobic microorganisms. These results explained the higher bacterial activity and gas production rate and higher efficiency of MSW anaerobic digestion.

CONCLUSION The likely utilization of MSWI ashes as landfill cover was examined with anaerobic bioreactor. Four layers were arranged to simulate the co-disposal of MSW and MSWI ashes. From the analysis of leachate parameters and gas production, it was noted that MSWI ashes addition could provide the appropriate alkalinity, adequate released metals and near neutral pH offer. These results particularly with neutral pH 7 and adequate released metal concentration including alkali metals, trace metals and heavy metals associated with the hydroxides and carbonates ensure the suitable and beneficial anaerobic environment for the MSW digestion. The resulting environment suitable for the anaerobic digestion explained the higher gas production rate and stimulatory MSW anaerobic digestion found in the ashes added bioreactor as compared to the control one.

REFERENCES [1] [2] [3] [4] [5] [6]

[7]

[8]

Bertolini, L.; Carsana, M.; Cassago, D.; Curzio, A. Q.; Collepardi, M. (2004). MSWI ashes as mineral additions in concrete. Cement and Concrete Research 34, 1899-1906. Deschamps, R. J. (1998). Using FBC and stoker ashes as roadway fill: a case study. J. Geotech. and Geoenviron. Eng. 124, 1120-1127. Hjelmar, O. (1996). Disposal strategies for municipal solid waste incineration residues. J. Hazardous Materials 47, 345-368. Lo, H. M. (2005). Metals behaviors of MSWI bottom ash co-digested anaerobically with MSW. Resources, Conservation & Recycling 43, 263-280. Ağdağ, O.N., Sponza, D.T., (2005). Effect of alkalinity on the performance of a simulated landfill bioreactor digesting organic solid wastes. Chemosphere 59, 871-879. American Public Health Association, American Water Works Association, Water Environment Federation. (1995). Standard methods for the examination of water and wastewater. 19th edition, Hanover, Maryland, US. Raskin, L.; Stromley, J. M.; Rittmann, B. E.; Stahl, D. A. (1994). Group-specific 16S rRNA hybridization probes to describe natural communities of methanogens. Appl. Environ. Microb. 60, 1232-1240. Parkin, G. F.; Owen, W. F. (1986). Fundamentals of anaerobic digestion of wastewater sludges. J. Environ. Eng. 112, 867-920.

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Takashima, M.; Speece, R. E. (1990). Mineral requirements for methane fermentation. Crit. Rev. Environ. Control 19, 465-479. Kayhanian, M.; Rich, D. (1995). Pilot-scale high solids thermophilic anaerobic digestion of municipal solid waste with an emphasis on nutrient requirements. Biomass and Bioenergy 8, 433-444. Paulo, P. L.; Jiang, B.; Cysneiros, D.; Stams, A. J. M.; Lettinga, G. (2004). Effect of cobalt on the anaerobic thermophilic conversion of methanol. Biotechnology and Bioengineering 85, 434-441. Fish, C. Ph. D. thesis, Enhance of the anaerobic digestion of municipal solid waste through nutrient supplementation. University of Southampton, Southampton, UK, 1999. Zandvoort, M. H.; Gieteling, J.; Lettinga, G.; Lens, P. N. L. (2004). Stimulation of methanol degradation in UASB reactors: in situ versus pre-loading cobalt on anaerobic granular sludge. Biotechnology and Bioengineering 87, 897-904. Dichtl, I. N. (1997). Thermophilic and mesophilic (two- stage) anaerobic digestion. J. CIWEM 11, 98-104. House, S. J. & Evison, L. M. (1997). Hazards of industrial anaerobic digester effluent discharges to sewer. J. CIWEM 11, 282-288. Bhatti, Z. I.; Furukwa, K. and Fujita, M. (1996). Feasibility of methanolic waste treatment in UASB reactors. Wat. Res. 30(11), 2559-2568.

INDEX A access, 204 accumulation, vii, 1, 91, 96, 114, 116, 243 acetic acid, 142 acetone, 9, 33, 159 acid, 9, 14, 20, 21, 25, 26, 39, 44, 48, 99, 102, 103, 105, 106, 108, 111, 120, 121, 123, 124, 125, 128, 130, 131, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 148, 149, 150, 153, 159, 170, 185, 187, 191 acidity, 106 acrylonitrile, 11, 28 activated carbon, x, 155, 156, 157, 158, 159, 160, 161, 164, 169, 170, 171, 173, 174, 185, 186, 187, 188, 189, 190, 191, 193, 194, 195 activation, 159, 160, 164, 165, 166, 167, 168, 169, 170, 171, 174, 180, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195 active site, 189 actual output, 122 additives, vii, 1, 4, 18, 20, 22, 23, 26, 28, 29, 31, 32, 36, 40, 100, 102, 132, 136, 142, 223 adhesion, 13, 27, 30 adhesives, 4, 14, 50 adjustment, 101 adsorption, xi, 32, 108, 157, 160, 169, 171, 172, 173, 174, 185, 187, 188, 189, 191, 193, 221, 224 advertising, 35 aerospace, 31 affect, 13, 14, 15, 17, 25, 26, 46, 106, 111, 138, 169, 210, 222, 223 Africa, viii, 62, 65, 73, 83, 86, 215 agent, 14, 22, 26, 29, 36, 40, 43, 164, 165, 166, 167, 168, 169, 170, 185, 189 agglutination, 15, 16

aggregates, xi, 221, 222, 223, 224, 230, 232, 233, 234 aggregation, 101 aging, 25, 54 agriculture, 99, 156, 157, 192 air emissions, 156, 159 air quality, 156, 161 alcohol, 9, 26, 193 alcohols, 9, 12, 20, 25 alkaline earth metals, 103 alkaline hydrolysis, 21, 44 alloys, 63, 69, 121, 125, 126, 138 alternative, vii, 1, 4, 26, 31, 47, 49, 156, 157, 158, 160, 208, 223 alternatives, 32, 163, 184, 193 aluminium, 130 aluminum, 50, 111, 120, 127 ambient air, 144 ambiguity, 146 amendments, 156 amines, 24, 26 ammonia, 48, 142 ammonium, 96, 102, 103, 107, 132, 140, 141, 142, 153 amplitude, 11 anaerobic sludge, xi, 235, 238, 239 animals, 98, 199 anxiety, 144 APC, 5 appropriate technology, 6, 147 aqueous solutions, 10, 14, 44, 160 argument, 46, 48 Aristotle, 155 aromatic hydrocarbons, 99 ash, x, xi, 47, 48, 118, 120, 121, 122, 125, 126, 128, 129, 130, 134, 147, 148, 149, 153, 157, 161, 162, 163, 164, 178, 179, 187, 189, 193, 221, 223, 224,

248

Index

225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 236, 237, 239, 241, 242, 243, 244 assessment, 49, 63, 92, 117, 118, 145, 214, 218, 219, 223, 233 assignment, 210 assumptions, 214, 215, 216 atmospheric pressure, 33, 172, 173, 176 atoms, 11, 20, 21 attacks, 21 attention, ix, 5, 44, 100, 103, 120, 158, 162, 198 attractiveness, 203 Australia, 65, 73, 133, 145 Austria, 79, 145, 206 availability, ix, 33, 35, 36, 63, 74, 85, 86, 90, 91, 93, 95, 96, 106, 110, 114, 116, 117, 121, 133, 161, 187, 214, 222 awareness, 4, 134, 136, 150

B bacteria, 161, 241 barriers, 3, 209 base catalysis, 22 baths, 14 batteries, 48, 121, 125, 133, 134, 136, 138, 139, 140, 141, 142, 145, 148, 149, 153 beams, 28 behavior, xi, 13, 17, 22, 27, 38, 116, 222, 223, 224, 225, 227, 230, 231, 232 Belarus, 214 Belgium, 46 bending, 8 benzene, 9, 45 binding, 15, 222, 223, 224 bioavailability, 97 biodegradability, 3 biodegradation, xi, 18, 31, 106, 236, 238 biodiversity, 215 biofuel, 200, 217 biomass, x, 99, 116, 155, 156, 161, 162, 164, 174, 175, 178, 179, 190, 191, 192, 194, 195, 201, 211, 212, 213, 214, 215, 217 biomass materials, 156, 179 biomedical applications, 63, 69 bioremediation, 94 biosphere, 94 biotechnology, 241 bismuth, 62 blends, vii, 1, 6, 27, 28, 29, 35, 36, 38, 50 blocks, xi, 222, 231, 232, 233 blood, 144, 145 body, 134, 138, 144 bonds, 11, 20, 22, 108

boric acid, 143 brain, 144 branching, 20, 22 brass, 121, 126, 128, 130, 147 Brazil, 5, 14, 34, 50 buildings, 192, 198 Bulgaria, 206, 214 burning, xi, 2, 8, 98, 160, 187, 235, 237 butadiene, 11, 28, 163

C cables, 136, 149 cadmium, ix, 48, 98, 119, 120, 123, 124, 128, 129, 131, 132 calcium, 12, 14, 45, 138 calorimetry, 7, 29 Canada, viii, 47, 52, 62, 65, 73, 83, 86, 94, 117, 136, 139, 145 cancer, 32 carbon, x, 2, 20, 21, 45, 63, 95, 97, 102, 103, 104, 108, 116, 125, 155, 156, 157, 158, 159, 160, 161, 164, 169, 171, 173, 174, 179, 180, 182, 184, 185, 186, 187, 188, 189, 190, 191, 192, 194, 201, 208, 210, 215, 238, 241 carbon atoms, 20, 21, 187 carbon dioxide, 156, 187, 194, 201, 208, 210, 215, 241 carbon monoxide, 45 carbonization, 164, 165, 166, 167, 168, 169, 170, 171, 194 carboxylic groups, 21 carcinogenesis, 144 case study, 191, 220, 244 cast, 121, 130, 136, 137, 138 catalyst, 18, 51, 91, 147, 157, 190 catalytic effect, 46 cation, 97 CEE, 205, 206, 208 cell, viii, 61, 62, 63, 64, 66, 67, 68, 69, 74, 75, 76, 77, 78, 80, 81, 84, 85, 90, 92, 130, 142, 148 cellulose, 8, 34, 35, 36, 40, 96, 183, 189, 194 ceramic, 148, 233 certificate, 210, 212, 213, 216, 219, 220 chain scission, 19, 20, 21, 22 chelates, 111 chemical bonds, 22, 108 chemical degradation, 18 chemical industry, 64, 69 chemical properties, 15, 99, 106 chemical reactions, 63, 175, 189, 195 chemical structures, 20 China, 50, 65, 73

Index chlorine, 8, 20, 45 chloroform, 9 chromatography, 103, 178, 184 chromatography analysis, 178 chromium, ix, 119, 120 circulation, 172 classes, 23, 231 classification, 16, 111, 214 clean technology, 140 cleaning, 13, 14, 15, 16, 22, 32, 33, 123, 158, 198, 199 cleavage, 18, 21, 22, 51 climate change, 2, 215 closure, 126 CO2, 2, 47, 164, 165, 166, 167, 168, 169, 170, 185, 187, 188, 190, 192, 193, 194 coal, x, 46, 105, 116, 118, 132, 143, 158, 184, 195, 205, 221, 223, 224, 226, 227, 232 coatings, 136 cobalt, 123, 130, 142, 245 coke, 168, 188 colic, 144 combustion, viii, 2, 4, 8, 47, 48, 49, 61, 63, 105, 128, 156, 158, 163, 185, 192, 193, 199, 203, 234 commodity, 50, 159 common rule, 217 communication, 203 community, 47 compatibility, 22, 30, 123, 222 compatibilizing agents, 28 competition, 159, 183, 215 competitiveness, 151 complexity, 33 compliance, 50, 147, 223, 225, 230, 231, 234 components, 2, 4, 5, 6, 22, 26, 27, 28, 30, 31, 37, 38, 43, 45, 47, 49, 50, 94, 99, 109, 145, 149, 157, 213, 222 composites, 6, 16, 31, 32, 35, 38, 39 composition, ix, 6, 11, 13, 15, 22, 27, 28, 29, 36, 39, 40, 41, 45, 46, 86, 102, 103, 119, 120, 122, 134, 136, 137, 161, 163, 179, 180, 194, 208, 222, 223, 224, 227, 231, 233, 238 composting, ix, 94, 99, 100, 101, 102, 106, 107, 108, 109, 110, 112, 115, 117, 199, 204, 236 compounds, 13, 14, 24, 25, 26, 31, 47, 96, 106, 108, 121, 134, 136, 137, 142, 147, 157, 158, 159, 160, 168, 177, 236, 237, 243 concentrates, 122, 139 concentration, x, xi, 14, 15, 16, 21, 23, 26, 32, 36, 38, 39, 43, 63, 72, 73, 86, 114, 116, 120, 122, 127, 142, 145, 146, 236, 242, 244 concrete, xi, 221, 224, 228, 230, 231, 232, 233, 234, 244

249

conditioning, ix, 93 conduct, xi, 235, 237, 239 conduction, 13 conductivity, xi, 3, 27, 95, 178, 236, 241, 242 confidence, 148 configuration, 160 conflict, x, 197, 202, 203, 209, 210, 212, 215, 216 consensus, 25 conservation, vii, 99, 108, 114, 121 consolidation, 151 constant rate, 243 construction, xi, 17, 49, 50, 122, 128, 158, 216, 221, 222, 233 consumer goods, 6 consumers, 4, 32, 209, 210, 211 consumption, vii, 1, 2, 3, 18, 23, 34, 44, 49, 62, 64, 66, 78, 79, 80, 121, 125, 133, 139, 148, 212, 215 contaminant, 21, 32, 33, 188 contamination, 13, 14, 15, 32, 33, 100, 105, 106, 117, 122, 146, 236 context, 216 control, xi, 51, 101, 111, 112, 117, 121, 123, 134, 135, 138, 144, 145, 146, 149, 150, 156, 159, 169, 176, 188, 217, 235, 237, 241, 242, 243, 244 conversion, 138, 157, 159, 160, 161, 162, 180, 182, 186, 190, 191, 194, 210, 212, 245 cooling, 130, 176, 177, 178, 217 copolymers, 28 copper, viii, ix, 8, 61, 63, 64, 86, 89, 90, 91, 93, 94, 98, 99, 105, 119, 120, 128, 129, 130, 131, 134, 145, 147, 202 corn, 156, 164, 166, 167, 168, 169, 170, 171, 190, 191 corona discharge, 38 correlation, 38, 39, 205, 207, 213, 216 corrosion, 163, 201 cost-benefit analysis, 22 costs, 14, 33, 34, 94, 95, 201, 203, 204, 209, 211, 215, 217 cotton, x, 31, 155, 156, 157, 161, 163, 164, 165, 168, 169, 176, 179, 183, 190, 193, 195 couples, 141 coupling, 17, 30 coverage, 174 covering, 10 creep, 20 critical value, 19 Croatia, 218 crop production, 108, 116, 215 crude oil, 45 crying, 35 crystallinity, 17, 19, 20, 22, 26, 39 crystallites, 35

250

Index

crystallization, 17, 19, 22, 33 crystals, 127, 141 cultivation, 157 curing, 125, 223, 227, 228 currency, 35 cycles, viii, 61, 63, 90 cycling, 96, 115 cyclohexanone, 9 cyclones, 13 Cyprus, 206, 214 Czech Republic, 206, 208

D damage, 34, 98, 125, 134, 135, 144 decay, 32 decision making, 198 decisions, x, 197, 198, 213, 216 decomposition, 20, 44, 45, 46, 51, 96, 97, 106, 109, 164, 174, 175, 238, 243 decomposition reactions, 20, 44, 45 deficit, 202 definition, 94, 99, 204, 214 deforestation, 106 degradation, ix, 14, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 45, 55, 94, 96, 105, 117, 120, 142, 146, 164, 228, 245 degradation mechanism, 18, 21 degradation process, 17, 22, 23, 26 degree of crystallinity, 17, 39 dehydration, 46 demand, viii, ix, xi, 5, 34, 35, 50, 61, 62, 63, 65, 67, 68, 72, 73, 74, 75, 77, 78, 82, 83, 85, 86, 89, 90, 91, 119, 120, 121, 122, 125, 126, 133, 134, 150, 198, 212, 213, 215, 218, 222, 236, 240 denitrification, 108 Denmark, 46, 145, 206, 207, 208, 209, 218 density, xi, 6, 10, 11, 14, 19, 20, 35, 37, 39, 40, 41, 97, 102, 136, 141, 148, 161, 162, 179, 189, 191, 221, 222, 224, 227, 228, 229, 230, 232 Department of Energy, 219 depolymerization, 19, 44, 51 deposition, ix, 93, 94, 98, 99, 114, 141 derivatives, 26 desorption, 171, 173, 185 destruction, 169, 187, 206, 208, 216 detection, 241 developed countries, vii, 3, 6, 34, 144 developed nations, 146, 150 DFT, 75, 92 diaphragm, 142 differential scanning, 7, 29 differential scanning calorimetry, 7, 29

differentiation, 209 diffusion, 16, 17, 18, 22, 32, 33, 199 digestion, xi, 102, 103, 204, 235, 236, 240, 241, 242, 243, 244, 245 dioxin, 48, 208, 244 directives, 50, 157, 203, 216, 225 discharges, 245 dispersion, 28, 30, 31, 37 displacement, 127, 227 dissociation, 20 dissolved oxygen, 172 distillation, 33, 127, 148, 153 distilled water, 185, 225, 238 distribution, 19, 26, 31, 45, 64, 107, 109, 110, 112, 160, 188, 190, 192, 225, 226, 227 district heating, x, 49, 197, 198, 199, 201, 203, 205, 213, 214, 215, 218, 219 diversity, 32 division, 5, 33 DMF, 9 domain, 22 donors, 23 drainage, 95, 99, 101 drinking water, 116, 189, 191 drying, 15, 16, 17, 33, 36, 227 DSC, 29 DSM, 220 ductility, 136 dumping, ix, 119, 145, 146, 149 durability, 3, 234 duration, 16, 20, 165, 169 dusts, 121

E earnings, 5 earth, 45, 63, 103, 134 Eastern Europe, 205 economic systems, 64 economics, 6, 159 ecosystems, viii, 93, 94, 96, 116, 117 effluent, 13, 14, 15, 47, 123, 149, 177, 245 egg, 34 elasticity, 228, 232 elasticity modulus, 228, 232 elastomers, 20 electric conductivity, 3, 27 electricity, x, 47, 49, 127, 128, 197, 198, 200, 202, 204, 205, 208, 209, 210, 211, 212, 213, 215, 216, 217, 219, 220 electrodes, 63, 141, 177 electrolysis, 125, 130, 141, 147 electrolyte, 128, 130, 132, 141, 142

Index electron microscopy, 39 electrons, 63 emergence, 3 emission, 2, 39, 46, 69, 79, 138, 139, 144, 203, 204, 210, 218, 223 employment, 215 energy consumption, 44, 139, 148 energy recovery, 2, 3, 4, 48, 49, 139, 192, 200, 203, 204, 205, 207, 208, 218, 219 energy supply, 214, 215, 217 England, 56 enlargement, 169 entropy, 27 environment, vii, viii, ix, 2, 3, 34, 44, 62, 63, 90, 91, 95, 98, 112, 117, 120, 125, 134, 135, 138, 145, 146, 149, 152, 153, 156, 157, 158, 159, 183, 192, 199, 218, 236, 237, 244 environmental awareness, 136 environmental change, 95 environmental control, 149 environmental degradation, 105, 120, 146 environmental effects, 215 environmental impact, viii, 2, 3, 15, 44, 61, 62, 63, 86, 123, 125, 148, 150, 159, 207, 213, 214, 222, 224 environmental protection, 123 Environmental Protection Agency, 122, 212, 220 environmental regulations, 151 enzymes, 110 epidemic, 98 equilibrium, 17, 23, 26 equipment, x, 10, 11, 14, 25, 45, 46, 199, 221, 226, 228 erosion, 108 EST, 219 ester, 21, 22 ester bonds, 22 Estonia, 206 etching, 36 ethanol, 157, 195 ethyl alcohol, 9 ethylene, 5, 20, 28, 36, 44, 45, 51, 142 ethylene glycol, 44 EU, 4, 46, 79, 156, 198, 203, 205, 211, 214, 216 Euro, 94 Europe, 4, 5, 52, 98, 118, 127, 192, 202, 204, 209, 213, 217 European Commission, 204, 209, 217 European Community, 4, 192, 217 European Parliament, 217 European Union, x, 4, 197, 198, 201, 203, 204, 208, 209, 216, 225 evidence, 18, 38

251

evolution, 142 exchange rate, 200 experimental condition, 12, 227 expertise, 147 exploitation, 51, 157, 158 exports, 215, 216 exposure, 22, 32, 98, 144 expulsion, 226 external costs, 215 extraction, 11, 33, 58, 63, 64, 103, 112, 120, 123, 130, 131, 132, 147, 152 extrusion, 10, 13, 15, 16, 26, 31, 32, 33, 34, 35, 36, 41, 44

F fabrication, 7, 29, 31, 35 failure, 13 farms, 91 fat, 212 fatigue, 144 FDA, 34 fermentation, 245 ferrite, 132 fertilization, 95, 98, 111, 112, 116 fibers, 30, 31 filler particles, 35, 36, 39 fillers, 16, 20, 30, 31, 35, 36, 38, 158 films, 15, 16, 29, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 51 filtration, 103, 161 financial support, 51, 150, 216 financing, 202 Finland, 65, 73, 98, 206, 208 fires, 199 firms, 62 fixation, 106, 108, 234 flame, 8, 17, 31 flame retardants, 17, 31 flexibility, 3, 20, 132, 139, 140, 223 flora, 99 flotation, 12 flue gas, 159, 188, 199 fluid, 14, 28, 33 fluidized bed, 123, 142, 158, 164 fluorescence, 225 focusing, 45 food, xi, 22, 32, 33, 34, 35, 47, 50, 57, 58, 156, 212, 215, 235, 238 food additives, 32 food industry, 212 food production, 215 forest ecosystem, viii, 93, 94

252

Index

forests, 102 formaldehyde, 46, 193, 194 formamide, 9 fossil, 2, 62, 98, 156, 157, 158, 160, 200, 204, 208, 209, 210, 211, 213, 215 France, 46, 136, 206, 208 free energy, 37 free radicals, 18, 19, 20, 21, 23, 26 free trade, 203, 204 free volume, 18 freezing, 105, 109 friction, 43 FTIR, 116 FTIR spectroscopy, 116 fuel, viii, 46, 49, 61, 62, 63, 64, 66, 67, 68, 69, 74, 75, 76, 77, 78, 80, 83, 84, 85, 86, 90, 91, 92, 136, 157, 158, 160, 180, 192, 199, 200, 201, 204, 205, 207, 208, 211, 213, 214, 215, 233

G garbage, 47, 59 gasification, 44, 45, 156, 158, 162, 165, 168, 180, 185, 190, 193 gasoline, 45, 47, 136 GDP, viii, 62, 65, 69, 74, 75, 76, 91 generation, ix, 3, 47, 63, 119, 121, 138, 140, 145, 146, 149, 157, 174, 217 germanium, 62 Germany, 4, 33, 79, 136, 139, 145, 194, 206, 208 glass transition, 13, 29 global demand, viii, 62, 65, 90 global economy, 118 glycol, 44 glycolysis, 44 GNP, 47 goals, x, 4, 197, 210, 212, 215, 216 gold, 63 goods and services, 219 government, 4, 34, 49, 50, 51, 91, 122, 199, 210, 211, 212 government budget, 210 grafted copolymers, 28 granules, x, 17, 130, 159, 221, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233 graphite, 142 grasses, 101 gravity, 125 Greece, 155, 178, 179, 190, 192, 206 green belt, 123 greenhouse gases, 2, 214 grids, 136, 137, 138 groups, 12, 17, 18, 20, 21, 22, 26, 36, 38, 92

growth, ix, 5, 34, 47, 62, 93, 95, 96, 108, 115, 199 growth rate, 47 guidelines, 122, 145

H habitat, viii, 93, 94 HALS, 23 harm, 145 harvesting, 114 hazardous substances, 199 hazards, 138 HDPE, 6, 7, 8, 9, 11, 12, 13, 14, 20, 25, 26, 28, 36 health, 32, 48, 111, 112, 134, 135, 138, 144, 160, 215, 236, 237 heat, x, 2, 13, 17, 19, 22, 26, 33, 47, 48, 49, 55, 123, 176, 179, 180, 182, 183, 184, 185, 187, 197, 198, 199, 200, 201, 203, 204, 205, 206, 208, 209, 210, 212, 213, 215, 218, 220 heat transfer, 176 heating, x, 41, 46, 49, 127, 140, 141, 148, 158, 160, 162, 164, 168, 170, 176, 179, 180, 182, 183, 190, 192, 198, 199, 204, 214, 217 heating rate, 164, 170, 176, 179, 180, 182, 183, 190 heavy metals, ix, xi, 47, 48, 94, 98, 99, 101, 105, 111, 112, 114, 115, 116, 117, 180, 199, 225, 230, 232, 236, 237, 242, 243, 244 height, xi, 11, 100, 101, 102, 228, 231, 235, 239 helium, 45, 172, 173, 176 high density polyethylene, 14 hip, 49 host, 63 humus, 96, 108, 109, 116, 117 hybridization, 244 hydrazine, 26 hydrocarbons, 63, 99, 159 hydrogen, 19, 20, 23, 45, 92, 156, 158, 159, 179 hydrogen gas, 45 hydrogenation, 44 hydrolysis, 2, 16, 18, 21, 22, 26, 44, 241, 243 hydroperoxides, 19, 20, 22, 24, 25, 26 hydrophilicity, 31 hydrophobicity, 12 hydroxide, 14, 45, 128, 143, 148, 153, 194 hydroxyl, 19, 21 hypertension, 144 hypothesis, 109

I ideas, 6 identification, 6, 7, 9, 16, 53, 146

Index implementation, ix, 4, 15, 119, 121, 134, 144, 147, 204, 209, 215 imports, 121, 122, 126, 146, 147, 149, 208 impregnation, 167 impurities, 5, 20, 22, 26, 128, 129, 130, 142, 147, 148, 160, 201 incentives, 4, 212 inclusion, 17, 31, 63 income, 5 incompatibility, 30 India, v, ix, 50, 119, 121, 122, 125, 126, 128, 133, 134, 138, 139, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153 indication, 174, 215, 241 indices, vii, 1 indigenous, x, 120, 121, 122, 199 indium, 62 induction, 20 induction period, 20 industry, ix, 2, 3, 32, 35, 46, 47, 49, 64, 69, 76, 79, 80, 93, 100, 105, 125, 133, 134, 135, 147, 148, 149, 150, 151, 153, 157, 158, 192, 200, 202, 218, 233, 234 influence, 13, 30, 38, 41, 43, 46, 95, 100, 116, 161, 162, 203, 211, 213, 237, 242 infrared spectroscopy, 7 infrastructure, 208, 209, 216 ingestion, 32 initiation, 18, 22, 24 inorganic fillers, 16, 36, 38 input, 70, 97, 116 insight, 195 institutions, ix, 119 instruction, 35 instruments, x, 197, 198, 210 insulation, 96 insulators, 20 integration, 153, 178, 218 intensity, 31, 38 interaction, 15, 30, 189 interactions, 26, 29, 39 interest, 31, 38, 50, 125, 149, 158, 159, 199, 209, 211 interface, 27, 28, 30, 35, 37, 41 interfacial adhesion, 30 interphase, 27, 28 interpretation, 213 interval, 211 intrinsic viscosity, 18, 44 inversion, 27 investment, x, 69, 128, 134, 197, 198, 199, 202, 203, 211 investors, 50

253

ions, 21, 63, 98, 123, 125, 141, 142, 189, 236, 237, 238, 241 Ireland, 206 iron, 121, 127, 128, 130, 132 isolation, 177 isophthalic acid, 44 isotherms, 171, 174 Italy, 136, 149, 192, 206, 208, 221, 224, 225, 226, 234

J Japan, 4, 46, 98, 116, 127, 136, 152 jobs, 156, 157 Jordan, 47

K kidney, 98 kidneys, 144 kinetic model, 175, 189 kinetic parameters, 175, 176, 189 kinetics, 20, 24, 45, 188, 189, 190, 191, 192, 194 knowledge, 22, 49, 198, 213, 216 KOH, 44, 165, 167, 168, 170, 171, 174, 185, 188, 189, 190, 194, 195 Kola Peninsula, viii, ix, 93, 94, 95, 97, 98, 99, 117 Korea, 139 Kyoto agreement, 156 Kyoto protocol, 201, 204

L labor, 6 lack of confidence, 199 lamination, 35 land, ix, 11, 50, 93, 94, 98, 99, 100, 102, 105, 107, 114, 115, 124, 125, 134, 145, 149, 157, 214, 215, 236 land use, 215 landfills, 2, 47, 48, 50, 123, 125, 145, 199, 204 Latvia, 206 laws, ix, 14, 47, 50, 119, 144 lead, ix, 2, 18, 19, 27, 31, 41, 48, 62, 85, 90, 91, 118, 119, 120, 121, 124, 125, 126, 130, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 148, 150, 151, 152, 153, 156, 157, 159, 209, 215 lead-acid battery, 141 learning, viii, 62, 68, 75, 92 legislation, x, 150, 197, 198, 200, 202, 203, 209 liberation, 19

254

Index

licenses, 147 life cycle, 62, 91 life span, viii, 62, 65, 67, 69, 73, 74, 78, 81, 84, 85, 86, 90, 158 lifetime, 223 light scattering, 225 light transmittance, 38 lignin, 12 limitation, 2, 31 linear programming, 213 links, x, 197, 228 liquid phase, 160 liquids, 8, 37, 174, 177, 184 Lithuania, 206 location, 99, 140 logistics, 3 long distance, 3 long run, 120, 125 low density polyethylene, 6 low temperatures, 20, 32, 136, 137 lower prices, 63 Luxemburg, 46 lying, 123

M macropores, 187 management, vii, viii, ix, x, 1, 3, 4, 47, 59, 62, 64, 78, 80, 83, 84, 85, 90, 120, 145, 146, 149, 150, 157, 158, 197, 201, 202, 204, 212, 214, 216, 217, 218, 219, 220 manners, 146 manufacturing, 2, 3, 4, 6, 34, 35, 126, 157, 200 market, vii, x, 1, 3, 5, 17, 31, 33, 34, 35, 50, 64, 65, 66, 67, 68, 69, 74, 75, 80, 84, 90, 91, 130, 133, 136, 158, 159, 189, 197, 198, 202, 203, 205, 206, 207, 208, 209, 216, 217, 218, 220 market penetration, 74, 75, 84, 90 market share, 67, 68, 69, 75, 80, 205, 206, 207, 208 market structure, 209 marketing, 6 markets, vii, 2, 4, 30, 34, 202, 204 mass, xi, 15, 34, 51, 97, 106, 110, 158, 184, 186, 189, 227, 235, 237 mass loss, 106 matrix, 14, 17, 18, 19, 20, 23, 24, 25, 26, 27, 30, 31, 32, 35, 40, 41, 50, 103, 108, 148, 223, 224, 234 measurement, 222, 228, 229, 230, 238 measures, 91, 120, 123, 138, 145, 199, 201, 213 mechanical degradation, 18 mechanical properties, 27, 30, 31, 227, 231, 233 media, 3, 44, 137 Mediterranean, 157

MEK, 9 melt, 18, 19, 24, 35, 132 melt flow index, 18 melting, 13, 15, 29, 35, 72, 128, 135, 136, 139 memory, 144 men, 145 mercury, ix, 98, 119, 120, 159, 172, 188 metabolism, 97 metal extraction, 120 metal hydroxides, 241 metal recovery, 147 metals, viii, ix, xi, 20, 23, 26, 47, 48, 49, 61, 62, 63, 64, 66, 73, 74, 86, 90, 91, 93, 94, 95, 98, 99, 101, 103, 104, 105, 106, 111, 112, 113, 114, 115, 116, 117, 119, 120, 121, 134, 136, 151, 180, 191, 225, 231, 236, 237, 238, 240, 241, 242, 243, 244 methanol, 44, 245 methodology, 13, 198, 214, 215 methyl methacrylate, 46 methylene chloride, 9 MFI, 18 microcavity, 35, 39 micronutrients, xi, 98, 120, 125, 130, 236, 244 microorganism, 14, 101 microstructure, 41, 160, 234 migration, 17, 33 mineral water, 21 mining, 10, 65, 72, 86, 89, 91, 98, 123, 125, 156 missions, 48, 215 mixing, 22, 27, 31, 134, 138, 228 MMA, 28, 46 mobile phone, 50 mobility, 18, 26, 30, 123, 203, 223 mode, 13, 134 modeling, 76, 87 models, x, 86, 175, 197, 198, 213, 214, 216 modern society, 198 modules, 92 modulus, 27, 30, 37, 228, 232 moisture, 16, 95, 96, 101, 156, 176, 178, 179, 180, 182, 184, 185 moisture content, 96 molar volume, 172 mole, 172 molecular weight, 19, 22, 25, 26, 160 molecules, 12, 26, 98, 160, 172, 173, 189 monitoring, 48, 100, 112, 122, 125, 134, 145, 147, 149, 150, 203 monolayer, 33, 36, 172, 173 monomers, 2, 19, 48, 51 morphology, 22, 27, 28, 29, 37, 39 Moscow, 117 motivation, 34

Index movement, 121, 146 multilayer films, 35, 41, 51 MWD, 19, 45

N Na2SO4, 141, 142 NaCl, 132 naphthalene, 45 natural gas, 157, 158, 160, 185, 201, 202, 205, 210 natural resources, vii, 2, 3, 98 needs, ix, 13, 15, 26, 120, 147, 198, 212, 236 negotiation, 210 nervous system, 144 nervousness, 144 Netherlands, 61, 79, 91, 116, 206, 233 network, 199, 202, 207, 209, 210, 218 newspapers, 202 nickel, viii, ix, 61, 63, 64, 86, 89, 90, 91, 93, 94, 98, 99, 105, 119, 120 nitrification, 96 nitrobenzene, 9 nitrogen, 47, 63, 102, 103, 106, 108, 116, 159, 164, 171, 172, 173, 190 nitrogen fixation, 106 nitrogen gas, 172, 173 node, 142 nodes, 130, 141 noise, 123 non-renewable resources, 47 North America, 46 Norway, 117, 206, 208, 209 novel materials, 3 nucleation, 35 nuclei, 35, 226 nutrients, ix, 93, 95, 96, 99, 106, 108, 109, 242 nutrition, 98, 116

O obligation, 32 observations, 99 oil, 4, 7, 14, 45, 46, 128, 155, 156, 178, 192, 199, 201, 207, 208, 214 oils, 15, 46, 192 optical properties, 18, 38 optimization, 6, 49, 91, 156, 215, 223, 226 ores, viii, 62, 63, 64, 72, 74, 86, 87, 88, 89, 90, 91, 125, 139 organ, 144 organic chemicals, 32, 45, 161 organic compounds, 31, 47, 96, 108, 157, 158, 160

255

organic matter, ix, x, 15, 93, 95, 96, 106, 108, 109, 115, 116, 117, 155, 179, 223 organic polymers, 12, 108 organism, 120 organizations, 6 orientation, 35, 41 outline, 11, 223 output, 70, 122, 205 overtime, 68, 75, 78, 80, 82, 83 oxidability, 103 oxidation, 18, 20, 22, 24, 25, 36, 125 oxides, 47, 132, 138 oxygen, xi, 18, 19, 20, 21, 22, 25, 45, 132, 142, 152, 156, 159, 160, 169, 172, 178, 179, 180, 204, 236, 240 oxygen absorption, 20

P packaging, 4, 5, 6, 7, 12, 14, 22, 26, 28, 32, 33, 34, 35, 36, 50, 53, 57, 58, 202, 204, 210, 218 paints, 14, 120, 125, 136 palladium, 62, 63, 91 palliative, 39 parameter, 41, 85, 153, 186 particles, 11, 12, 13, 17, 29, 31, 35, 36, 39, 40, 41, 48, 98, 114, 142, 157, 180, 195 pastures, 115 patents, 35 pathways, 48, 97, 114 peat, 212 percolation, 27 permeability, 27, 101 permit, 99 perspective, 158, 202, 211, 212, 215, 216, 218 Peru, 52 PET, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17, 18, 21, 22, 26, 28, 31, 33, 34, 36, 44, 45, 50, 51, 52, 54, 57, 58 PGE, 63, 64, 91 pH, xi, 8, 14, 15, 32, 101, 102, 104, 105, 106, 107, 108, 109, 112, 113, 128, 138, 185, 236, 237, 240, 241, 242, 243, 244 phenol, 9, 23, 24, 25, 26, 193 phosphates, 25, 243 phosphorus, 25, 96, 108 photodegradation, 18 photooxidation, 17 physical and mechanical properties, 27, 222 physical properties, 22, 63, 116, 162, 230 phytoremediation, 114 pilot study, 219 pine, 102

256

Index

planning, 49 plants, vii, ix, 1, 47, 48, 49, 71, 93, 95, 96, 97, 98, 101, 103, 106, 108, 111, 112, 113, 114, 115, 116, 121, 122, 123, 133, 134, 136, 137, 139, 145, 148, 149, 156, 157, 158, 159, 160, 161, 192, 199, 200, 201, 203, 204, 205, 208, 209, 210, 211, 212, 213, 216, 217, 220 plasma, 127 plastic products, vii, 1, 3 plastics, vii, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 13, 14, 15, 16, 17, 23, 27, 28, 30, 31, 32, 34, 36, 44, 45, 46, 48, 49, 50, 51, 53, 57, 58, 208, 211 plastics processing, 23 platinum, viii, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 90, 91, 92 PMMA, 8, 9, 46, 51 Poland, 206, 208 polar groups, 38 polarity, 26, 38 policy instruments, x, 197, 198, 200, 210, 213, 216, 218 politics, 218 pollutants, ix, 14, 63, 93, 94, 98, 99, 100, 104, 105, 114, 117, 156, 157, 158, 160, 222, 223 pollution, viii, x, 15, 34, 47, 48, 93, 94, 95, 98, 100, 101, 104, 105, 106, 109, 113, 114, 117, 120, 121, 123, 134, 138, 144, 146, 149, 150, 156, 159, 223, 236, 237 poly(vinyl chloride), 6 polyamides, 45 polycarbonate, 19 polydispersity, 18 polyesters, 22, 45 polyethylene sack, 101 polyethylenes, 8 polymer blends, 35, 38, 50 polymer chains, 18, 19 polymer composites, 30, 31, 56 polymer matrix, 14, 17, 18, 19, 20, 23, 24, 25, 26, 30, 31, 32, 35, 41, 50 polymer oxidation, 20 polymer structure, 17 polymerization, 17, 26, 33, 108 polymers, vii, 1, 2, 6, 8, 9, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 25, 27, 28, 29, 36, 37, 38, 44, 45, 54, 55, 108, 110 polyolefins, 8, 14, 19, 20, 25, 28, 35, 36, 40, 45, 46, 51, 54, 55 polypropylene, 6, 14, 20, 35, 36, 137, 149 polystyrene, 6, 7, 8, 17 polyurethane, 44, 45 polyurethanes, 50

pools, ix, 93, 96, 110 poor, ix, 3, 31, 93, 97, 107, 114, 231 population, viii, 5, 47, 50, 62, 65, 69, 135, 236 population growth, 47 population size, viii, 62, 65, 69 porosity, 97, 157, 160, 171, 174, 186, 188, 191, 222, 230 Portugal, 93, 206 potassium, 14, 44, 129, 168, 188, 194 power, x, 1, 20, 46, 47, 49, 105, 156, 157, 158, 159, 160, 180, 190, 197, 198, 199, 200, 201, 204, 205, 211, 212, 213, 220, 226 power plants, 157, 158, 159, 160, 199, 200, 201 practical activity, 3 precipitation, 104, 105, 111, 125, 130, 132, 143 prediction, 192 preference, 112 preparation, 101, 137, 138, 148, 158, 164, 169, 180, 187, 190, 191, 194, 195, 238 pressure, 16, 20, 26, 33, 44, 45, 62, 147, 161, 171, 172, 173, 174, 176, 177, 186 prevention, 204, 217 prices, 63, 200, 202, 203, 204, 205, 209 primary antioxidants, 23, 24 principle, 32 probability, 20 probe, 12, 102, 103 producers, 121, 132, 133, 147, 202, 206, 212 product design, 6 production, viii, ix, x, xi, 3, 5, 16, 18, 23, 27, 33, 34, 49, 51, 61, 62, 63, 64, 65, 66, 68, 70, 71, 72, 73, 75, 78, 79, 80, 82, 85, 86, 89, 90, 91, 92, 93, 99, 106, 108, 110, 116, 119, 120, 121, 122, 123, 125, 127, 133, 134, 136, 137, 138, 139, 147, 148, 150, 151, 152, 153, 155, 156, 157, 158, 159, 160, 161, 162, 164, 174, 183, 186, 189, 190, 191, 192, 193, 195, 197, 198, 201, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 224, 232, 234, 236, 237, 240, 241, 242, 243, 244 productivity, 6, 96 profitability, 47 program, 43, 47 proliferation, 101 propagation, 18, 23, 25, 30, 37 proposition, 36, 199, 210 propylene, 20, 28 protocol, 204 PTFE, 9, 51 public awareness, 4 public health, 32, 134 publishers, 59 Puerto Rico, 91 pulse, 228

Index pultrusion, 32 pure water, 16 purification, 121, 123, 125, 128, 129, 130, 132, 144, 147, 148, 161, 189 PVC, 6, 7, 8, 9, 10, 11, 12, 13, 22, 136 pyrolysis, x, 2, 44, 45, 46, 51, 155, 156, 158, 159, 160, 162, 163, 164, 166, 169, 174, 175, 176, 178, 180, 181, 182, 183, 184, 185, 187, 189, 190, 191, 192, 193, 194, 195 pyrolysis gases, 158 pyrophosphate, 110

Q quantitative technique, 39 quaternary ammonium, 234

R radiation, 11, 36 range, 11, 13, 30, 98, 107, 109, 125, 126, 140, 145, 160, 169, 170, 174, 176, 178, 180, 182, 186, 188, 226, 228, 229, 230, 231, 232, 233, 241 rape, 190 raw materials, vii, x, 1, 43, 44, 120, 121, 128, 132, 147, 150, 156, 158, 159, 169, 188, 189 reaction mechanism, 23, 46 reaction rate, 20, 169 reagents, 14, 45 recombination, 20 recovery, ix, x, 2, 3, 4, 36, 46, 48, 49, 50, 51, 53, 94, 95, 119, 123, 124, 127, 128, 134, 135, 136, 137, 138, 139, 140, 143, 147, 148, 149, 150, 151, 153, 155, 156, 158, 197, 198, 199, 202, 203, 204, 206, 207, 210, 212, 216, 221, 222, 223, 225, 236 recovery processes, 36, 48 recycling, vii, viii, x, 1, 2, 3, 4, 5, 10, 13, 14, 15, 16, 17, 26, 27, 28, 31, 32, 33, 34, 36, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 57, 59, 61, 62, 63, 65, 66, 68, 71, 72, 74, 80, 81, 85, 86, 89, 90, 91, 114, 120, 123, 125, 126, 128, 132, 136, 137, 139, 141, 146, 147, 148, 149, 150, 151, 152, 153, 155, 158, 160, 190, 195, 202, 208, 211, 214, 217, 218, 233, 236 redistribution, ix, 94 reduction, vii, 1, 2, 18, 25, 47, 68, 125, 139, 141, 148, 187, 236 refining, 72, 116, 138 regenerated cellulose, 8 regional problem, 47 regression, 78, 86, 176 regression analysis, 78, 86, 176

257

regulation, 32, 230, 231 regulations, 3, 4, 5, 48, 50, 51, 146, 151, 200, 211 rehabilitation, ix, 93, 99, 100, 102, 104, 105, 114 reinforcement, 30, 31 reinforcing fibers, 31 relationship, 227, 231 relaxation, 13 relaxation properties, 13 relevance, 14 remembering, 12 replacement, 38, 158, 222, 228 reprocessing, vii, 1, 2, 14, 15, 16, 17, 18, 22, 26, 31, 32, 132, 134, 146, 147 residues, vii, ix, x, 1, 2, 3, 4, 5, 6, 11, 12, 13, 14, 15, 17, 20, 22, 26, 27, 28, 30, 31, 32, 33, 34, 36, 44, 45, 46, 47, 48, 49, 50, 51, 117, 119, 120, 121, 123, 125, 126, 127, 140, 146, 148, 155, 156, 157, 159, 161, 162, 163, 164, 165, 168, 169, 179, 186, 189, 190, 194, 208, 233, 236, 244 resins, 4, 11, 34, 36, 168, 193 resistance, 18, 22, 26, 37 resolution, 5 resource availability, 63, 86 resources, vii, viii, 2, 3, 47, 62, 63, 64, 65, 66, 72, 73, 74, 78, 79, 80, 81, 82, 83, 84, 85, 86, 89, 90, 91, 98, 114, 136, 156, 158, 201, 204, 213, 217 respiration, 96, 109, 110 responsibility, 3, 5, 50, 204, 218 restructuring, 217 retardation, 238 returns, 121 revenue, 158 rice, 64, 98, 156, 164, 166, 167, 168, 169, 170, 171, 179, 191, 193 rice husk, 156, 168, 169, 170, 179, 191 risk, 32, 48, 98, 120, 138, 144 robustness, 214 Romania, 206, 208, 214 ROOH, 19, 20, 24 room temperature, 11, 28, 102, 103, 172, 173, 177, 227 roughness, 36, 39 rubber, 5, 28, 29, 31, 137, 158, 163, 208 rubbers, 163 runoff, 108 Russia, viii, ix, 50, 62, 65, 73, 83, 93, 94, 99, 117

S safety, 14, 25, 32, 114, 120, 138, 149 sales, 123 salts, 98, 108, 125, 141, 152, 170

258

Index

sample, 41, 102, 103, 110, 170, 172, 173, 176, 177, 180, 182, 185, 187, 188, 189, 225 sampling, 100, 102, 103, 109, 110, 112, 113, 234 saturation, 97, 171, 172, 173 savings, 2, 47, 49, 211 sawdust, 191 Scandinavia, 98 scanning calorimetry, 7, 29 scanning electron microscopy, 39 schema, 218 scores, 48 search, 23, 161 Second World, 199 security, 3 sediments, 222, 223 seed, 157, 171, 186, 188, 190, 193 selectivity, 45 self, vii, 1, 8, 20, 21, 203 SEM micrographs, 42 sensitivity, 47, 97, 214 sensors, 63, 69 separation, vii, 1, 4, 5, 6, 10, 11, 12, 13, 15, 16, 27, 48, 50, 72, 124, 125, 128, 134, 137, 147 series, 20, 45, 59, 130, 132, 141, 187, 228 services, 151, 203, 214 sewage, ix, 14, 93, 95, 99, 100, 102, 106, 107, 108, 110, 114, 116, 117, 118, 234 shape, 13, 17, 22, 23, 26, 162, 163, 179 shear, 18, 31, 41 shortage, 4, 49 sign, 227 signals, 213 silica, 140, 178 silver, 134, 135 simulation, 68, 83, 217 SiO2, 35, 124, 126, 135, 148, 224 sites, ix, 20, 71, 83, 99, 119, 120, 146, 150 skimming, 120, 122, 125, 126, 127, 128, 147, 149 skin, 138 slag, ix, 119, 120, 123, 132, 134, 135, 139, 140, 151, 223, 234 Slovakia, 206, 208 sludge, ix, xi, 93, 95, 99, 100, 101, 102, 106, 107, 108, 110, 112, 114, 116, 117, 118, 120, 124, 125, 138, 140, 141, 148, 222, 233, 234, 235, 238, 239, 245 smoke, 8 social problems, 215 sodium, 14, 44, 138 sodium hydroxide, 14 soil particles, 157 soils, 95, 96, 110, 115, 116, 117, 118, 134 solid phase, 15, 16

solid polymers, 22 solid state, 14, 22, 25 solid waste, ix, xi, 3, 46, 94, 99, 114, 116, 119, 120, 125, 134, 145, 146, 148, 149, 150, 158, 163, 190, 194, 208, 219, 222, 223, 232, 233, 235, 236, 244, 245 solidification processes, 223 solubility, 10, 11, 22, 25, 107, 127 solvents, 8, 9, 32, 44, 50 sorption, 32 South Africa, 83 Spain, 136, 151, 206 species, 35, 94, 106, 114, 115 specific gravity, 125 specific surface, 171, 173, 185, 188, 237 specificity, ix, 93 spectrophotometry, 103 spectroscopy, 7, 11, 116 spectrum, 11, 160, 174 speed, 36, 41, 82, 83, 90, 226 spindle, 157 sports, 4 stability, 18, 20, 23, 25, 26, 31 stabilization, x, 22, 23, 24, 25, 48, 54, 55, 221, 223, 224, 234 stabilizers, 17, 23, 24, 25, 26, 36, 54 stages, x, 5, 49, 120, 128, 171, 174, 187 standard of living, 47 standards, 37, 107, 145, 203, 214 statistics, 207 steel, 120, 128, 132, 177, 180, 185, 202, 228 stock, viii, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 83, 86, 87, 88, 90 stockpiling, 134 storage, 32, 50, 123, 141, 157, 158, 160, 218, 236 strategies, 94, 117, 150, 215, 244 streams, 74, 137, 138, 157, 158, 160 strength, xi, 27, 28, 30, 86, 222, 223, 224, 228, 229, 230, 231, 232 stress, 13, 19, 27, 30, 31, 37, 114 stretching, 41 structure formation, 169 students, 51 styrene, 11, 28, 163 subsidization, 211 substitutes, 190 substitution, 51, 78, 143 substrates, 39 subtraction, 171 sugar, 164 sulfur, 24, 156, 159 sulfuric acid, 9, 102 sulphur, 123, 138, 189

Index summer, 110 Sun, 191, 193, 234 supervision, 217 suppliers, 51, 209 supply, viii, ix, 16, 34, 35, 49, 61, 62, 63, 65, 72, 73, 74, 81, 82, 83, 85, 86, 87, 89, 90, 91, 119, 120, 121, 122, 126, 133, 155, 156, 158, 159, 198, 201, 204, 205, 208, 214, 217, 218 supply disruption, 155 suppression, 123 Supreme Court, 147 surface area, 17, 26, 36, 157, 160, 169, 171, 172, 173, 185, 186, 187, 188, 189, 190, 191, 194 surface energy, 12, 30, 38, 39 surface layer, 35, 41, 43 surface tension, 16, 27, 37 surface treatment, 12, 33, 38, 43 surfactant, 12, 14 surplus, 101, 205 survival, 114 susceptibility, 14, 17, 18, 22, 38 sustainability, vii, 1 sustainable development, vii, 2, 3, 49, 51, 62, 222 Sweden, x, 46, 47, 92, 118, 140, 197, 198, 200, 202, 203, 204, 205, 206, 207, 208, 209, 210, 216, 217, 218, 219, 220 Switzerland, 46, 151, 152, 153, 206, 208 synthesis, 44 synthetic fiber, 30, 31 system analysis, 91, 213 systems, vii, viii, x, 1, 3, 15, 16, 25, 26, 50, 54, 64, 93, 94, 144, 156, 161, 197, 198, 201, 202, 208, 209, 210, 213, 214, 215, 218, 219, 227, 228, 229

T Taiwan, xi, 48, 116, 235, 236, 237, 238 targets, 4, 21, 50, 156, 214 taxation, 3, 50, 200, 201, 208, 209, 210, 211, 217, 219 technology, viii, 6, 10, 30, 44, 56, 58, 61, 63, 64, 90, 120, 121, 123, 125, 132, 133, 134, 139, 140, 147, 149, 150, 151, 152, 153, 158, 180, 199 teeth, 144 temperature, x, 11, 13, 14, 16, 18, 20, 22, 26, 28, 29, 32, 33, 41, 44, 45, 48, 96, 99, 102, 103, 109, 110, 127, 128, 129, 130, 142, 143, 155, 160, 164, 167, 169, 170, 171, 172, 173, 174, 176, 177, 178, 180, 181, 182, 183, 184, 185, 186, 189, 192, 201, 223, 227 tensile strength, 30 tension, 16, 19, 20, 27, 28 test procedure, 41

259

tetrahydrofuran, 9, 11 TGA, 164, 165, 166 theory, 37 thermal aging, 25 thermal decomposition, 175, 195 thermal degradation, 18, 22 thermal oxidation, 20 thermal stability, 25 thermal treatment, 94, 156, 158, 191 thermodynamics, 2, 27 thermolysis, 44, 45, 46, 48 thermooxidation, 17, 18 thermoplastics, 14, 17, 31 threat, 144 threshold, x, 32, 120, 149, 244 timber, 35 time, vii, viii, 7, 10, 11, 16, 17, 27, 45, 47, 62, 65, 66, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 83, 85, 90, 98, 108, 110, 134, 147, 156, 157, 159, 164, 166, 167, 170, 174, 175, 176, 180, 182, 183, 185, 186, 187, 189, 199, 201, 202, 210, 223, 241 tissue, 113 titanium, 40, 141 toluene, 9 total energy, 215 toxicity, 31, 32, 106, 111, 112, 145, 148 toys, 4 TPA, 44, 45 trade, 24, 146, 147, 198, 203, 209, 217 trading, x, 159, 197, 198, 203, 204, 210, 218 training, 6 transference, 30 transformation, ix, 94, 99, 108, 109, 110, 112, 114, 115 transformations, 108 transition, 13, 20, 28, 29, 99 transition metal, 20 transition temperature, 13, 28 transitions, 13 transparency, 3 transplantation, 101 transport, 3, 34, 50, 75, 98, 145, 150 transportation, 198, 211 trees, 99, 101, 161 trend, 80, 114, 174, 186, 200, 230, 242 trial, 43 tundra, 96, 99, 115, 116 Turkey, 118, 206 turnover, ix, 93, 96

260

Index

U UK, 4, 75, 92, 115, 116, 117, 132, 136, 145, 152, 153, 192, 206, 245 Ukraine, 214 uncertainty, 186 uniform, 163, 179 United Nations, 114 United States, 57, 122, 157 urban centers, 3 UV, 11, 19, 23, 36 UV radiation, 36

V vacuum, 16, 33, 114, 156, 192 values, x, 27, 38, 40, 43, 46, 48, 75, 78, 86, 96, 103, 104, 107, 109, 112, 120, 123, 130, 159, 172, 173, 186, 187, 188, 228, 229, 230, 231, 232, 241 vapor, 16, 161, 171 variability, 28 variable, 69, 132, 145 variables, viii, 32, 38, 62, 65, 67, 69, 73, 76, 86, 223, 233 variance, 99 variation, 108, 209 VAT, 209 vegetables, 7, 34 vegetation, ix, 93, 94, 99, 105, 114 vehicles, viii, 50, 61, 62, 63, 67, 68, 69, 74, 75, 76, 77, 78, 79, 91, 92, 136, 157, 158, 160, 204 velocity, 15, 16, 228 vinyl chloride, 6 viscosity, 18, 28, 30, 44 volatility, 47 volatilization, 107, 108 vulcanization, 159

W washing procedures, 14 waste disposal, 47, 48, 189 waste incineration, x, 47, 197, 198, 199, 200, 201, 203, 204, 205, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 218, 219, 220, 221, 233 waste management, vii, viii, ix, x, 1, 47, 62, 64, 78, 80, 83, 84, 85, 90, 120, 146, 150, 158, 197, 198,

200, 201, 202, 203, 205, 208, 211, 212, 213, 214, 216, 222 waste treatment, x, 94, 189, 197, 198, 200, 201, 203, 205, 207, 210, 211, 213, 214, 215, 216, 222, 245 waste water, 116, 238 wastewater, xi, 156, 235, 241, 244 water, xi, 7, 8, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 26, 33, 35, 36, 39, 44, 46, 48, 50, 96, 98, 101, 102, 103, 108, 110, 112, 116, 117, 120, 122, 123, 125, 130, 134, 138, 142, 145, 148, 150, 160, 178, 185, 188, 190, 200, 203, 210, 211, 212, 218, 221, 224, 226, 227, 228, 229, 236, 238, 241, 244 water absorption, 227, 229 wavelengths, 11, 19 wear, 158 weight loss, 26, 175, 183, 189 weight ratio, 29 Western Europe, 216 wettability, 37 wheat, 156, 161, 190 wind, 91, 98, 212 winter, 105, 110, 115, 193 women, 98, 145 wood, x, 3, 31, 46, 49, 155, 162, 163, 164, 174, 178, 179, 180, 183, 189, 192, 208, 212 words, 5, 86, 94, 114, 120 work, vii, x, 2, 3, 12, 14, 15, 16, 28, 29, 33, 36, 39, 48, 107, 123, 145, 147, 148, 160, 168, 175, 187, 199, 216, 221, 224, 232 workers, 5, 6, 18, 26, 29, 33, 44, 45, 47, 49, 50, 134, 135, 138 writing, 28, 34, 35, 37, 38, 210

Y yield, 45, 46, 51, 86, 149, 164, 171, 175, 176, 181, 182, 183, 184, 190

Z Zimbabwe, 65, 73 zinc, ix, 11, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 145, 146, 147, 148, 149, 150, 151, 152, 153, 170, 191 zinc oxide, 122, 124, 128, 130, 132, 147, 148 zirconium, 51 ZnO, 125, 128, 132, 135, 148