Treatise on Water Science vol III (Aquatic Chemistry and Biology)

Preface – Aquatic Chemistry and Biology FH Frimmel, Karlsruhe Institute of Technology, Karlsruhe, Germany & 2011 Elsevier B.V. All rights reserved.

The World of Aquatic Chemistry and Microbiology Aquatic chemistry and microbiology do not belong to the classical subjects taught in universities. Nevertheless, they are part of many curricula in natural sciences and engineering. It is beyond doubt that the fascination of the molecular dimension of water itself and all its constituents, which goes like a red threat through all the aspects of structure, transport, and reactions of and in aquatic systems, attracts so many people. Due to the broad and fundamental importance of water for life, including the humans, the molecular water sciences (MoWaS) have to be transdisciplinary. The discipline includes not only physics, chemistry, biology, and geology, but also mathematics, engineering, and economics and even parts of social sciences. As a consequence, several subjects have developed based on fundamental ones but focusing on the special aspects of water, examples of which include limnology, oceanography, hydrogeology, hydrology, groundwater dynamics, drinking water treatment, municipal water management, industrial water usage, wastewater treatment, and hydrothermal usage. Many of them either are cross-linked or bridge the gap to the fields of quantitative water management. The big challenge when dealing with MoWaS can be deduced from the nano- and microscale of the substances involved and their low concentrations. The related bio-response can range from subtle to acute toxic effects. Methods to obtain reliable results are still scarce, especially for applications in natural environment. Here, the influences of matrices and the synergetic or antagonistic effects in multicomponent samples are often unclear. It is well accepted that water is the fundamental basis for our known life and in its unique function cannot be replaced by anything else. The physical properties of liquid water are reflected in its properties as transport medium, reaction phase, and mediator for higher molecular structures. One of the most impressive properties of the water molecules is the ability to form intermolecular hydrogen (H)-bonds. Linus Pauling once said, ‘‘y the hydrogen bond is especially suited to play a part in reactions occurring at normal temperatures, and I believe that it will be found that the significance of the hydrogen bond for physiology is greater than of any other single structural feature.’’ In other words, the formation and breaking of H-bonds in the energy band of our common environmental situation deliver the key for understanding life and its supporting element – water. It is also obvious that all major changes in water quality and temperature, for example, as a result of climate change, must have an influence on the dynamics of reactions and on the material balances involved. This again will influence the water cycle and hence the aquatic resources. Here, water management comes into the focus. Different kinds of water use with different influences on water quality in small- or large scale must be considered. Industrial development and population growth have led to one of the biggest

challenges to supply sufficient and hygienically safe water for human consumption and food production. Severe water shortage and necessary water quality are issues that have arisen regionally and are predicted to intensify drastically during the following decades. Concepts for multiple water use and water reuse need to be developed, taking advantage of the specific hydrological, climatic, and ecological situations. In addition, the special demands of social communities such as mega cities or developing countries have to be considered. Wherever possible, the ecological functions of regions must be protected for it is most reasonable to use nature as a self-sustained system also for water cleaning. The protective function of soils and their capability to degrade and eliminate aquatic pollutants make it attractive to use groundwater as a resource for drinking water supply, especially when protective zones and assisting technical measures are established. Toxicity and hygiene reflecting criteria are, besides the technical aspects such as corrosivity, most important for the use of water. A meaningful assessment of the use-oriented water quality has also to include parameters which quantify, for example, biota friendliness, potential for bacterial growth, eutrophication, and disinfection by-product formation. Occurrence of pathogenic microorganisms and waterborne epidemic episodes belong to the most serious events often with peaks in wars, natural disasters, and badly managed camps, homes, and companies. Quite often, shortcuts between the systems for drinking water supply and wastewater discharge have been identified as reason. Economic aspects are one of the master drivers for use of water and its management. On the one hand, the availability of enough water of suitable quality has been discussed as an issue of human rights. On the other hand, water has become a trade good, which is sold directly in bottles or through pipes or as virtual water in the manifold forms of industrial products. No matter how much profit might be involved in this business, the availability of reasonable resources and economically feasible treatment technologies will play a fundamental role. The application of cheap energy sources such as sun light and the use of homogeneous and heterogeneous catalysis, including biocatalysis, lead to most promising watertreatment concepts. Intelligent combination and an optimized sequence of treatment steps can further improve the economy of water plants. Hybrid systems are suited for highly efficient water treatment in fast working small reactors with the advantage of decentralized application. Keeping these aspects in mind, it becomes obvious that understanding the details of the properties of living and nonliving water constituents, their reactivities, and transport behavior will help to tailor powerful methods for waterquality assessment and to derive efficient concepts for timely water-treatment processes. The water cycle is an ideal case study not only for its different stages and hot spots, but also as

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Preface – Aquatic Chemistry and Biology

a whole which can teach us the systematic approach to complex systems and to the solutions of the related man-made problems. It also shows the necessity of transdisciplinary thinking in the sense of lifelong learning. Starting in the early days of childhood, we need to lay the foundation for a responsible care for water as a basis for our life and culture. Furthermore, we need to invest in the tools for a sustainable water management by developing measures to save the water cycle in its proper ecological function. This calls for the classical components of teaching and research and beyond that for innovative concepts to serve the daily needs of water usage in an economically affordable and socially acceptable way. To serve this aim, a comprehensive treatise on water is presented. Volume 3 of this work includes the chemistry and microbiology of MoWaS. The analytical aspects cover water-specific sum parameters, methods for the determination of trace metals and metalloids, as well as radioactive substances, and the characterization of natural organic matter (NOM). Emerging contaminants, colloids, and engineered nanoparticles are presented and data handling is described. The identification of bacteria and parasites helps to characterize the hygienic status of water. Online monitoring,

screening of estrogen activities, and enzyme-linked immunotests show the way to modern concepts for continuous quality control and bioeffect-related assessment. The development and application of standardized methods supply tools to obtain reproducible and well-comparable results. For the special needs of water treatment and distribution, it is most useful to quantify biodegradability and toxic effects. Reaction mechanisms of oxidation and disinfection processes as well as bioremediation are important not only to understand the pathways of technical transformations and natural attenuation, but also to optimize treatment strategies. All these topics are addressed by leading experts in the field. They all intend to supply for the interdisciplinary water community the molecular facts for a meaningful diagnosis of the status of aquatic systems and for efficient technical processes within the water cycle. As the editor of this volume, I would like to thank all the authors for their valuable contributions. Furthermore, I am grateful to U. Bilitewski, T. Bu¨nger, G. Donnevert, G. Gauglitz, H. Geckeis, B. Hambsch, T. Hofmann, H. Horn, T. P. Knepper, D. Knopp, V. Neitzel, R. NieXner, B. Nowack, F. Petry, H.-J. Pluta, M. Spiteller, and M. Weller for their input by peerreview.

3.01 Sum Parameters: Potential and Limitations FH Frimmel and G Abbt-Braun, Karlsruhe Institute of Technology, Karlsruhe, Germany & 2011 Elsevier B.V. All rights reserved.

3.01.1 3.01.2 3.01.3 3.01.3.1 3.01.3.1.1 3.01.3.2 3.01.3.2.1 3.01.3.3 3.01.3.4 3.01.3.5 3.01.3.5.1 3.01.3.5.2 3.01.3.5.3 3.01.3.6 3.01.4 3.01.4.1 3.01.4.2 3.01.4.2.1 3.01.4.2.2 3.01.4.2.3 3.01.4.2.4 3.01.4.3 3.01.4.3.1 3.01.4.3.2 3.01.4.3.3 3.01.4.3.4 3.01.4.4 3.01.4.4.1 3.01.4.4.2 3.01.4.4.3 3.01.4.4.4 3.01.4.4.5 3.01.4.5 3.01.5 3.01.5.1 3.01.5.2 3.01.5.3 3.01.5.4 3.01.6 3.01.6.1 3.01.6.2 3.01.6.3 3.01.6.4 3.01.7 3.01.7.1 3.01.7.2 3.01.7.2.1 3.01.7.2.2 3.01.7.2.3 3.01.7.2.4 3.01.7.3 References

Introduction General Considerations and Scope DOC and TOC Background Relevance Analytical Procedure Method variations Interferences Advanced TOC (DOC) Characterization Applications Hydrosphere Surface water Water treatment Surrogate Parameters Oxygen Demand Parameters Introduction Chemical Oxygen Demand Background Analytical procedure Interferences Applications PMC and Permanganate Index (IMn) Background Analytical procedure Interferences Applications Biochemical Oxygen Demand Background Analytical procedure Interferences Applications Related parameters (AOC) Interdependences UVA and Visible Range Absorbance Background Analytical Procedure Interferences Applications Organically Bound Halogens Adsorbable on Activated Carbon (AOX) Background Analytical Procedure Applications Related Parameters Additional Sum Parameters Background Examples for Emerging Parameters Humic substances NPs and colloids Luminescence Bioeffect quantification View

3 3 3 3 4 4 5 5 5 7 7 7 7 8 8 8 9 9 9 10 12 12 12 13 13 13 13 13 13 14 14 14 15 15 15 15 16 16 18 18 18 19 19 19 19 20 20 21 22 22 23 23

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Sum Parameters: Potential and Limitations

3.01.1 Introduction The general assessment of the quality of aquatic systems and the judgment of the efficiency of a water-treatment facility quite often relies on the application of sum parameters. Sum parameters are normally based on an integrative quantification of a specific group of compounds. However, the results obtained are mostly operationally defined and are often prone to misinterpretation. Therefore, it is essential to understand the power and at the same time the limitations of the parameters applied. Like signposts, they can give first information on assessment strategies and the necessity of singlecompound analysis. They are also suited for a total balance even in the presence of compounds with unknown structure (Frimmel and Abbt-Braun, 2009; Abbt-Braun and Frimmel, 2010). All these advantages have led to a prosperous development of water-specific sum parameters and their application in legislation, in technical rules, and in environmental recommendations. It is beyond doubt that research in and development of sum parameters have been significantly influenced by the practical aspects of water quality and vice versa. The applicability of the corresponding methods has also stimulated the development of specific instrumentation (see also Chapter 3.10 Online Monitoring Sensors). Some of the instruments are well suited for continuous measurements and can be used as online detectors. This opens the door for the resolution of mixtures by chromatography or by other fractionation methods. As a consequence, the sum parameter-based detector systems have an important bridging function between unresolved sum parameter quantification and single substance determination. All these aspects have led on the one hand to a tremendous increase of valuable information, but on the other hand to often uncritical interpretation of the results. The aim of this chapter is to focus on some well established sum parameters and to highlight their characteristics such as 1. 2. 3. 4. 5. 6.

background, principle of the method, interferences and limitations, advanced method, application, and related parameters.

3.01.2 General Considerations and Scope Sum parameters such as single-compound determination have to fulfill task-specific minimum requirements concerning exactness. It has to be decided whether the principle ‘as exact as possible’ or the approach ‘as exact as necessary’ meets best the requirements of the specific task. Often the desire for a specific and sensitive measurement finds its limitation in the needs of a high throughput of samples and/or a low economic investment. A reasonable compromise can normally be reached by a sound problem analysis prior to the determination itself. In general, classical spectroscopic and electrochemical methods cover the concentration range in aqueous samples from mg down to ng l1 (Skoog et al., 2003; Standard

Methods, 2005). This puts the application of sum parameters right into the center of a comprehensive assessment concept which is open for a dynamic back bonding of the results with the selection of further analytical steps. As a consequence, sum parameters have found their way into legislation and assessment of environmental protection with all the demands of data quality acceptance in court cases. In this chapter, we discuss in depth the parameters: dissolved organic carbon (DOC) and total organic carbon (TOC), chemical oxygen demand (COD), permanganate consumption (PMC), biochemical oxygen demand (BOD) and assimilable organic carbon (AOC), the color and ultraviolet (UV) absorbance (UVA), and on activated carbon adsorbable organically bound halogens (AOX). Most of these parameters refer to the dissolved state of the matter to be determined. Filtration through membranes with nominal pore size of 0.45 mm is widely used as analytical operation even though there might be pitfalls from pore blocking, fouling layer formation, or scaling. Quite often, the water samples are analyzed without pretreatment. This has to be clearly stated in the protocol and is normally assigned as total concentration value, for example, TOC. To close the gap between the dissolved state and particulate matter, a method for the determination of the particle-size distribution in the nanometer (nm) range is presented.

3.01.3 DOC and TOC 3.01.3.1 Background The basis for the parameters DOC and TOC is the chemical definition of organic compounds. They can be of biogeogenic or anthropogenic origin. Most natural organic substances in water are the left overs of biological activities and products of a huge variety of naturally occurring physical, chemical, and biochemical reactions in air, soil, and water. The endless number of possible substances involved in these processes makes the identification tedious and, from the quantitative point of view, impossible. Therefore, the terms natural organic matter (NOM) or humic substances (HSs) as the refractory part of it are often used for an integrative description, and the parameters DOC or TOC for quantification (Thurman, 1985; Frimmel and Christman, 1988; Perdue and Gjessing, 1990; Frimmel et al., 2002). Organic compounds of anthropogenic origin can find their way into the aquatic systems from effluents of wastewater treatment plants and industrial activities, from chemical wastes and landfills, by accidents during storage and transport of organic chemicals, and from combustion and by deposition from the air (Kolpin et al., 2002; Frimmel and Mu¨ller, 2006; Reemtsma and Jekel, 2006; Ku¨mmerer, 2008). In the current industrialized environment, it is quite idle to distinguish strictly between the purely natural components and the anthropogenic ones in many cases. Concerning the quantification for C, this might be irrelevant anyhow. Table 1 gives an overview of the different C species defined according to their character and/or to the pretreatment of the sample prior to elemental C determination. In practical work, the definitions often are only semi-quantitatively accurate.

Sum Parameters: Potential and Limitations Table 1

Common terms for property-related TOC fractions

POC) is retained together with the sorbed substances in/on the filter and the volatile compounds (volatile organic carbon, VOC) are normally lost:

Synonym

Meaning, definition

AOC BOC

Assimilable OC (see Section 3.01.4.4.5) Biodegradable OC (by microorganisms) (see Section 3.01.4.4) Chromatographable OC (by LC, GC, etc.) (see Section 3.01.3.4) Dissolved OC (o0.45 mm) Dissolved OM (E50% DOC) Natural OM (geogenic) Particulate OC (40.45 mm) Persistent organic pollutants Refractory OM (poorly biodegradable) Volatile OC (e.g., boiling point (substances)o80 1C)

COC DOC DOM NOM POC POP ROM VOC

OC, organic carbon; OM, organic matter.

3.01.3.1.1 Relevance The relevance of TOC can be deduced from its character as universal parameter. Other parameters reflecting specific properties of organic matter (OM) such as DOC or AOC or surrogate parameters such as UVA or COD can preferably be related to the TOC value to provide the basis for an especially meaningful comparison of water samples. However, it has to be kept in mind that TOC as sum parameter always remains limited in the information it can supply on the chemical structure of the matter it reflects. The instrumental tools suited for continuous TOC determination can be used as detection system for chromatographic TOC fractionation and by this it can help to overcome the limitation of structural information to some extent. The total carbon (TC) includes all C in inorganic and organic form (Equation (1)). The total inorganic carbon (TIC) reflects mainly the carbonate system (CO2, HCO3  , and CO3 2 ), and by definition also the traces of CO, CN, OCN, and SCN, which might be of relevance in specific wastewaters:

TC ¼ TIC þ TOC

5

ð1Þ

TOC comprises all the C atoms which are covalently bound in organic molecules and even particulate matter like carbon black. In natural aquatic systems and water technology, the carbonate system is considered to be most relevant due to its high mass concentrations. TIC can be quantified as CO2 after acidification (pHo2) and purging with an inert gas of high purity such as N2 or Ar. The purging step would also transfer other volatile substances such as HCN or small organic molecules such as methane (CH4), methanol (CH3OH), and C1or C2-halogen compounds from the aqueous phase to the gas phase. Due to the low concentrations of such volatile compounds in most waters, this is often neglected in the mass balances, but it can be important in the assessment of specific situations such as the occurrence of toxic substances. The TOC includes the organic carbon (OC) in dissolved and particulate matter. These two types of C can be distinguished by filtration through a 0.45-mm pore-size membrane, leading to the DOC in the filtrate. The particulate part (particulate organic carbon,

TOC ¼ DOC þ POCk þ VOCm

ð2Þ

This method has been widely accepted, even though there are still controversial debates on the influence of the mostly poorly defined filter cakes, on the results and whether the pore size of the filter should be chosen to be 0.1 mm or even below that to better reflect the dissolved state. A well acceptable way out of these problems can be seen in a detailed description of the experimental protocol of the method applied. The occurrence of TOC is a consequence of life on the Earth. The ubiquity of TOC in aquatic systems has been demonstrated in many investigations (Table 1). It is mostly refractory, that is, the biologically stable part of dissolved organic matter (DOC) which leads to a kind of steady-state TOC concentration in the different aqueous phases. DOC is often used synonymously with TOC, and other properties of the OM are reflected in specific parameters (Table 1). It is obvious that some terms and their definitions must remain vague. This means that the concerned parameter values can have a considerable span of uncertainty. Keeping this in mind, it seems to be acceptable to use Equation (3) as an approximation based on many elemental analyses. Unfortunately in literature, the databases are quite often unclear. Therefore, experimental data and procedures need to be described in detail and unambiguously to be useful:

rðDOMÞE 2rðDOCÞ

ð3Þ

3.01.3.2 Analytical Procedure Due to the high importance of TOC and DOC values in water assessment, there are standardized international methods for their determination (DIN EN 1484, 1997; Standard Methods 5310 B, 5310 C, 5310 D, 2005; see also Chapter 3.11 Standardized Methods for Water-Quality Assessment). They are mostly based on a quantitative oxidation of the organic molecules to CO2 which can be determined with a very low limit of determination around 10 mg l1. Oxidation is done either by high-temperature (up to 950 1C) combustion in the presence of a catalyst (e.g., platinum-group metals, cobalt oxide, or barium chromate) and oxygen or at ambient temperature in solution using UV irradiation and/or chemical oxidants such as H2O2 or persulfate. Inorganic C (IC) has to be removed within a pretreatment step, for example, by acidification with H3PO4 and purging as CO2. This separation step is most important for reliable TOC results, because TOC is quantified also as CO2 and this value is much smaller than the IC concentration in most waters. The CO2 produced from the inorganic carbonate system and from the organic water constituents can be (a) quantified in the gas phase after drying and transfer to a nondispersive infrared (IR) detector or (b) trapped in alkaline aqueous solution with coulometric titration. The principle of a system based on continuous flow injection of the sample is shown in Figure 1. Calibration can be done with defined aqueous potassium biphthalate (C8H5O4K) solutions for OC and with sodium

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Sum Parameters: Potential and Limitations

CO2 analyzer

CO2 analyzer

Inorganic CO2

Organic CO2

Purger

UV reactor

Aqueous sample

H3PO4

Data system

Liquid waste

K2S2O8

CO2-free air

CO2-free N2

Figure 1 System for continuous-flow TIC/TOC analysis.

carbonate (Na2CO3) solutions for IC. The different methods operate in the concentration range 10 mg l1or(C)o1 g l1.

3.01.3.2.1 Method variations There is another procedure for continuous-flow injection of the aqueous sample (Figure 2). After acidification and persulfate addition, the sample is split: one sample flow passes through the UV reactor, whereas the other one passes to a delay coil. The CO2 from each branch is separated by CO2selective membranes into high-purity water. There the increase in the electrical conductivity can be directly related to the CO2 concentration. The CO2 from the non-UV-irradiated branch represents the TIC, whereas the CO2 from the irradiated branch represents the TC. TOC results from the difference. Samples with relatively high levels of TOC (r(C)4mg l1) and/or suspended OC can be well determined by the hightemperature combustion method. This method is suited for online measurement. The inorganic carbon can be converted to CO2 by acidification (pHo2) and removed by purging or it can be quantified, for example, in a nondispersive IR detector. In the purged sample, OC can be quantified after high-temperature catalytic oxidation as CO2 (Figure 3). A variation of the method determines the TC of the sample after its direct injection into the combustion chamber which is kept at temperatures above 950 1C to decompose all carbonates. TIC and TOC or other carbon fractions can be deduced from the respective differences.

3.01.3.3 Interferences Special care has to be taken with TOC determination of suspensions. Often the analytical homogeneity and hence the representative character of a sample are endangered by sedimentation and its kinetics. A way out of that dilemma is the

Aqueous sample Acid Oxidant (K2S2O8)

Delay coil 6 min

UV reactor 6 min

Membrane module

Membrane module

CO2 detector (TIC)

CO2 detector (TC)

Data treatment TC − TIC = TOC Figure 2 Membrane-based procedure for the continuous-flow TIC/TOC analysis.

separate quantification of the concentration of particulate matter and that of the dissolved matter, for example, after applying filtration through a membrane with defined pore size. However, it has to be kept in mind that the filtration can be influenced by the type of membrane and its bleeding (Khan

Sum Parameters: Potential and Limitations

7

Inorganic CO2 (TIC) H2SO4 or H3PO4

Sample

Catalytic combustion chamber

Purging unit

Gas (air) CO2 free

O2 CO2 free

Organic CO2 (OC) (+ H2O, HCl …)

Cooler CO2 analyzer (non-disp. IR)

Figure 3 Experimental setup for the catalytic combustion method for TIC/TOC determination in aqueous solutions.

and Pillai, 2007), its surface tension, and age and state of equilibration. In addition, undefined pore blocking and sorption processes have to be considered. The DOC concentration at the beginning of a filtration experiment can be quite different to the DOC concentration at the end. For samples with high turbidity, filtration through a set of filters with decreasing pore size and determination of the fractions obtained can be a reasonable though time-consuming option. Another possibility is the determination of the colloidal index (CI, also known as silt density index SI or fouling index FI) for OC characterization (ASTM Standard D4189-07, 2007). The principle of the method is to relate the specific filtrate volumes with the time needed to obtain them as the filtration process proceeds. In case short-wavelength UV lamps are used to increase the amount of OH radicals for oxidation, care has to be taken as the intensity of the UV light may be reduced by highly turbid samples or by aging of the light source resulting in incomplete oxidation. Problems can also arise by chloride concentrations above 0.05 wt.%, due to preferential oxidation of chloride. At relatively low DOC concentrations as present in marine systems, special care has to be taken to guarantee correct results. Dafner and Wangersky (2002) showed that special attention toward the cleanness of the sampling facilities and procedure is crucial. Sample storage should be short (o2 days) at low temperature (o4 1C) and in the dark. Examples for field procedures to collect and preserve freshwater samples for DOC analysis were shown by Kaplan (1994), and Zsolnay (2003) addressed some basic problems and artifacts such as flock formation and agglomeration in sampling and preserving DOM from soil seepage water (see also Chapter 3.06 Sampling and Conservation, Chapter 3.07 Measurement Quality in Water Analysis). Blank samples should be run to determine background values of equipment, used chemicals, gases, and filters (in the case of DOC determination).

3.01.3.4 Advanced TOC (DOC) Characterization The great relevance of TOC and DOC parameters for the assessment of aquatic systems together with the available

powerful instrumentation for quantification paved the way for their advanced analysis. In addition to all, the intelligently designed experiments which are controlled by a suite of TOC or DOC measurements, a liquid chromatographic (LC) system with online DOC detection has been developed (Huber and Frimmel, 1994) for advanced OC characterization. Especially the principle of size-exclusion chromatography (SEC; e.g., TSK HW-50S or -40S turned out to be useful for the assessment of DOM and its behavior in water-treatment processes (Her et al., 2002b). The principle of the method is given in Figure 4. To reach high chromatographic resolution and low detection limits, special care has to be taken for low background levels of OC. This means that the phosphate buffer as mobile phase, the N2 carrier gas, and the phosphoric acid as acidifier for the CO2 purging of the inorganic carbonates have to be free of organic contamination. The sample can be injected to either pass the column or bypass it. This leads to the possibility of determining the amount of chromatographable OC and the TOC. Between the column and the spinning thin film photoreactor, noninvasive online UV/visible (Vis) and fluorescence detectors can be installed to give multi-dimensionally detected chromatograms. In principle, the retention times (or elution volumes) obtained for SEC columns are reversely correlated with the molecular size and in good approximation with the molecular weight of the eluted substances. The column elution can be calibrated with polyethylene glycols and/or polystyrene sulfonates. The exclusion volume (V0) and the permeation volumes (VP) can be determined by dextrane blue and methanol, respectively. However, the molecular size calibration bears some problems because aquatic TOC contains many unknown substances and hence calibration with authentic molecules is impossible (Lankes et al., 2009). Most common errors come from interfering adsorption and ion-exchange effects of the eluted substances in the stationary phase of the columns. A typical chromatogram of the OM in tap water obtained by UV (l ¼ 254 nm), fluorescence (lex ¼ 254 nm, lem ¼ 450 nm), and OC detection is given in Figure 5. The OC trace of the chromatograms of the injected water with a TOC concentration of 0.5 mg l1 shows a dominance of

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Sum Parameters: Potential and Limitations

Aqueous sample

Data logging processing Column (e.g., SEC)

Eluent (P-buffer)

Piston pump

Injection port

UV/Vis detector

Phosphoric acid

Carrier gas (N2)

Fluorescence detector

pH 2 Piston pump

Peltier condenser

UV thin film reactor

IR detector

Inorganic CO2

IR detector

Organic CO2

Liquid waste

Relative OC-, UV (254)-, fluorescence (450)-signal

Figure 4 Experimental setup for the size exclusion chromatographic characterization of aquatic OC.

Vp

V0

OC Fluorescence UV

1.0

0.5

0 20

40

60

80

Elution volume, Ve (ml) Figure 5 Multi-dimensional size exclusion chromatograms for tap water (Karlsruhe, sampling date 07.07.09; r(DOC) ¼ 0.5 mg l1; resin: TSK HW-50 S; eluent: phosphate buffer, 26.8 mmol l1; injection volume 2.5 ml).

high molecular substances between 40 and 50 ml of elution volume followed by a less large fraction. This material has a relatively strong UVA and does fluoresce. It is attractive to assign these fractions to refractory HSs of higher and lower molecular size. The relatively sharp chromatographic peak reflects small organic acids as reported by Brinkmann et al. (2003a, 2003b) and is followed by gradually eluting unidentified OC. There are some detector-specific differences in the fractions and in their relative intensities. In general, however, the main fractions look quite similar. As a consequence, the easy-tomeasure UVA is often used as surrogate parameter for OC determination (Her et al., 2002a, 2003). In the case of very low background values, fractions of a few tens of ng l1 OC can be quantified.

3.01.3.5 Applications The DOC methods and their combination with fractionation methods (e.g., SEC-UV/OC method) are well suited for the advanced characterization and semi-quantitative assessment of environmental processes such as nutrient cycling and pollutant transport as well as technical water-treatment processes. (see also Chapter 3.15 Characterization Tools for Differentiating Natural Organic Matter from Effluent Organic Matter).

3.01.3.5.1 Hydrosphere Typical ranges for TOC/DOC concentrations of aquatic systems are given in Table 2.

Sum Parameters: Potential and Limitations Table 2

9

DOC in different aquatic systems

Aquatic systems

DOC concentration (mg l 1) Average

References

Range

Ocean

0.5

0.3–2.0 in 0–300 m; 0.2–0.8 in 4300 m

Williams (1971); Duursma and Dawson (1981)

Freshwater Ice and snow Rivers Lakes

0.5 7 2.2

0.1–5.0 5–9 Oligotrophic 2–3 Eutrophic 9–16 10–50

Laird et al. (1988); Frimmel et al. (2002) Malcolm (1985); Sontheimer et al. (1986) Steinberg (2003); McKnight and Aiken (1998) Aitkenhead-Peterson et al. (2003); Bertilsson and Jones (2003) Thurman (1985); Frimmel and Abbt-Braun (1999)

19–31 B0.5 up to 10

Abbt-Braun (1992); Frimmel (1992) Dinar et al. (2006); Graber and Rudich (2006) Matthess et al. (1992); Wedepohl (1969)

Brown water Soil seepage water Rain Groundwater, CaCO3 aquifer

12 25 B1 0.7

3.01.3.5.2 Surface water

3.01.3.5.3 Water treatment

The SEC-UV/OC method finds a broad application in characterizing the OM of rivers. In Figure 6, typical chromatograms for (a) the river Rhine (Germany) and (b) the river Moskva (Russia) are shown. Although the DOC concentrations are significantly different, the main fractions of the OC for both rivers are quite similar, but the small-sized substances are more abundant in the case of the river Rhine. Both rivers show a small but significant OC fraction around the exclusion volume without any UVA. It could be shown that these substances are of high molecular carbohydrate type. For comparison, the chromatograms for water from a brown water lake (c) and for wastewater (d) are shown. The brown water is dominated by a single fraction and it is attractive to assign it to plant-derived matter of humic structure. In the case of the wastewater, there are obviously plenty of low-molecular-weight organic substances (acids) which get eliminated by biological treatment. As a result of biotreatment, a large organic fraction with low UVA is generated. Based on the assignment to matter with carbohydrate structures, this fraction around the exclusion volume of the SEC column can be used for a rough estimation of the allochthonous and autochthonous part of aquatic refractory OC. In large molecular size fractions, there was a predominance of polysaccharide material. N-Acetylated polysaccharides derived from microbial leftovers. Lignin and tannin derivatives were most abundant in the intermediate size fraction (Lankes et al., 2008). However, detailed interpretation has to rely on advanced spectroscopic information on molecular structure. For a critical evaluation of OC assignment, see, for example, AbbtBraun et al. (2004), Lankes et al. (2008), Reemtsma et al. (2008), and Kunenkov et al. (2009). Also, it has to be kept in mind that photochemical OC detection often does not work quantitatively, for example, up to 70% of certain OC compounds were not detected with the organic carbon detection system in systematic investigations (Lankes et al., 2009). Assuming that the majority of refractory OM components do absorb UV radiation, UVA values are a valuable supplement for OC detection.

The SEC-OC system can also be used to follow technical separation processes such as flocculation, membrane filtration, or adsorption. Figure 7 shows the example of bog lake (brown water) OC as it decreases after (a) addition of ferric chloride (flocculation with FeCl3) and (b) equilibration with increasing amounts of powdered activated carbon (PAC; adsorption). It is obvious that in flocculation most of the OM (87%) gets eliminated. Especially, the high-molecular-size substances get better eliminated than the small ones. Interesting to note is the high elimination yield of UV-absorbing matter and the relatively, poor elimination yield of AOX forming precursors. In the case of PAC adsorption, the rest OC which remains in solution is strongly dependent on the amount of PAC added as expected but it is mainly higher molecular matter which remains in solution. These findings can be explained by the limited availability of pores with larger size. All information that can be derived from advanced OC characterization does not only supply the basis for a better understanding of the mechanisms which rule the OC distribution, but it also opens the door for the development of technically relevant elimination processes and their optimization (see also Chapter 3.15 Characterization Tools for Differentiating Natural Organic Matter from Effluent Organic Matter, Chapter 3.16 Chemical Basis for Water Technology).

3.01.3.6 Surrogate Parameters There are a number of sum parameters for the determination of OM which have been developed independently or supplementary to the DOC/TOC methods. Most of them work simpler and therefore find a broad application as surrogate parameters for OC. They focus on a specific character of the present organic substances and can add valuable information for the assessment of water quality. Their specific information can be related to the mass unit of OC as a universal parameter and which can supply the basis for a sound assessment and comparison of different aquatic sources or for following a

10

Sum Parameters: Potential and Limitations 4 V0

OC UV

1.5 River water Rhine (Wörth) (OC) = 1.7 mg l−1

1.0

0.5

OC UV River water Moskva (Kolomna) (OC) = 8.5 mg l−1

3

2

1

0

0.0 20

40

60

2.5

20

80

Elution volume, Ve (ml)

(a)

30

40

50

60

70

80

Elution volume, Ve (ml)

(b)

Vp

V0

V0

OC UV Brown water HO23 (OC) = 27.7 mg l−1 dilution: 1:10

2.0

Vp

4

1.5

1.0

Relative OC-, UV (254)-signal

Relative OC-, UV (254)-signal

Vp

V0

Vp Relative OC-, UV (254)-signal

Relative OC-, UV (254)-signal

2.0

Wastewater (OC) (OC) = 24.9 mg l−1, dilution: 1:3

3

Wastewater effluent after biological treatment (OC) (OC) = 9.9 mg l−1

2

a: OC b: UV

1

a b

0

0.5 20 (c)

40

60

20

80

Elution volume, Ve (ml)

(d)

40

60

80

Elution volume, Ve (ml)

Figure 6 Size exclusion chromatogram detected by OC- and UV (l ¼ 254)-detection of river water ((a) river Rhine, (b) river Moskva), brown water ((c) Hohlohsee, HO23), and wastewater (dilution 1:3) and wastewater treatment plant effluent (d) (resin: TSK HW-50S; eluent: phosphate buffer, 26.8 mmol l1).

complete treatment pathway. Most common surrogate parameters and complementary parameters for OC are given in Table 3. They are discussed in the following sections in more detail.

3.01.4 Oxygen Demand Parameters 3.01.4.1 Introduction Despite the broad distribution, the stability of the nonradioactive elements leads to their quite constant total amounts on earth. However, their appearance in different compounds and phases called speciation makes them distinguishable according to the chemical bonds in which they are engaged (Pauling, 1960). The corresponding oxidation state of the atoms in their chemical appearance is a typical guide for their reactivity. Carbon is one of the elements which covers all the range of eight oxidation state levels from the lowest one of  IV in CH4 up to the highest of one of þ IV in CO2. The elemental form is represented by the graphite and diamond structure. CO2 is the common end product of all

biochemical degradation reactions of C-compounds and chemical combustions if sufficient O2 is available. According to the high importance of the load of organic substances in water, their oxidative transformation into CO2 has become the basis for the development of sum parameters for quality assessment (Wagner, 1973). Most of them are based on the quantification of the oxygen necessary for a more or less quantitative oxidation of all organic compounds. There are purely chemical methods and there are biochemical methods, using a mixed bacterial population.

3.01.4.2 Chemical Oxygen Demand 3.01.4.2.1 Background The aim of the COD is to obtain a complete oxidation of all organic compounds of an aqueous sample to CO2. This is best reached by wet oxidation with potassium dichromate (K2Cr2O7) in hot acid solution. Problems can arise from other water constituents, for example, inorganic ones, which also get oxidized under the reaction conditions. These disturbances can be tackled by elimination of the substances concerned or

Sum Parameters: Potential and Limitations

11

Elimination in % SAK254

AOX-FP

87

96

54

Relative OC-signal

Relative UV (254)-signal

DOC

20

40 60 80 Retention time, t (min)

100

After flocculation (FeCl3) Original

20

40

60

80

100

Retention time, t (min)

(a)

Brown water

Relative OC-signal

Remaining DOC + 50 mg l−1 PAC + 500 mg l−1 PAC + 1000 mg l−1 PAC

0 (b)

10

20

30

40

50

60

Retention time, t (min)

Figure 7 Size exclusion chromatogram obtained by OC detection (a, b) and UV detection ((a), inset) of diluted brown water and the remaining DOC after flocculation (a) and after adsorption on PAC (b) (TSK HW-50 S; eluent: phosphate buffer, 26.8 mmol l1; AOX-FP, AOX-formation potential; SAK, spectral absorption coefficient).

12

Sum Parameters: Potential and Limitations

by masking them such that they do not react. The oxidation reaction is given in Equation (4) and has a standard potential of E1 ¼ 1.36 V:

Cr2 O7 2 þ 6e þ 14H3 Oþ -2Cr3þ þ 21H2 O

ð4Þ

3.01.4.2.2 Analytical procedure The redox reactions with K2Cr2O7 work best under fairly concentrated H2SO4 conditions and at the elevated boiling temperature of the sample/acid mixture. The oxidative power of the defined amount of added dichromate is partly consumed by the known volume of the aqueous sample to be analyzed. The remaining gets quantified by reductive back titration with ferrous sulfate (Equation (5)). The color change from orange-yellow (Cr2 O7 2 ) to pale green (Cr3þ) is used as indicator for the equivalence point and for the final calculation of the result: Cr2 O7 2 þ 6Fe2þ þ 14Hþ -2Cr3þ þ 6Fe3þ þ 7H2 O

ð5Þ

The final result is calculated from the amount of consumed K2Cr2O7 converted into O2 equivalents according to

6:13  rðK2 Cr2 O7 Þ in mg l1  rðO2 Þ in mg l1

ð6Þ

The whole laboratory procedure is outlined in Figure 8. Table 3

Common surrogate parameters for OC in aquatic samples

Surrogate parameter

Acronym

Quantification as

Chemical oxygen demand Permanganate consumption Spectral UV and visible absorbance Biochemical oxygen demand Adsorbable organic halogens Various other sum parameters

COD PMC SUVA SVIA BOD AOX See Section 3.01.7 OC

O2 O2 A(254 nm) A(436 nm) O2 Cl

Organic carbon

CO2

HgSO4 1g Aqueous sample 50 ml

Ag2SO4 (50 mg) in H2SO4 (conc.) 5 ml

The method is broadly used in wastewater characterization. It works best in the concentration range 50 mg l1or(O2) o900 mg l1. Concentrations steps or dilution with organic free water are recommended if the COD concentrations are below 50 mg l1 or higher than 900 mg l1. In case ferrous ammonium sulfate (FAS) titrant and ferroin indicator are used, the color changes from blue-green to reddish brown. For COD determination, several standard methods have become available (DIN 38409-41, 1980; DIN 38409-43, 1981; DIN 38409-44, 1992; DIN ISO 15705, 2003; Standard Methods 5220 B, 5220 C, 5220 D, 2005); (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment). Method variations. In addition to the described open reflux method, there is the possibility to use a so-called closed reflux method which uses borosilicate culture tube-like digestion vessels of 10 ml or more capacity and 10–25 mm diameter with polytetrafluoroethylene lined tightly fitting caps. Alternatively, borosilicate ampules can be used. The tubes or ampules filled with sample and chemicals are inserted in a block digestor at 150 1C for 120 min reflux. After cooling to room temperature, the digested solutions are titrated with ferroin indicator and FAS titrant. Alternatively, the change of C2 O7 2 to Cr3þ can be quantified spectrophotometrically at l ¼ 600 nm. The first method is mostly used for COD concentrations r(O2)o90 mg l1 whereas the l ¼ 600 nm absorption turned out to be better suited for higher concentrations. Experimental kits for these methods are commercially available. Calibration of all versions of the COD method is preferably done by potassium hydrogen phthalate (C8H5O4K) standard solutions with concentrations within the concentration range concerned. The whole procedure and equipment should be the same as for the determination of the samples.

3.01.4.2.3 Interferences The COD method based on the oxidative Cr2 O7 2 reaction at boiling conditions leads to parameter values with a coefficient of variation o8%. Use of especially cleaned glassware (e.g., H2SO4 rinsing), at least duplicate determinations and the subtraction of the blank COD of reagents and dilution water in the applied procedure can improve the data. The relevance

Calculated result

Distilled water

Flask with reflux condenser 120 min boiling

K2Cr2O7 (42 mmol l−1) 25 ml

Titrator

Ferroin indicator FAS (*) (0.25 mol l−1)

Figure 8 Laboratory procedure for the determination of the COD with dichromate (*FAS, ferrous ammonium sulfate).

Waste

Sum Parameters: Potential and Limitations

of the determination of background values was pointed out by Wagner (1973). Samples below the normal concentration range ask for even more care. In these cases, a higher volume of sample and diluted K2Cr2O7 standard solution (0.004 M) together with the appropriate amount of reagents are used and all are concentrated under boiling conditions to a volume of 150 ml. Titration is done with standardized 0.025 M FAS. Substances which are prone to poor or incomplete digestion in all described versions of the COD method are pyridine, its derivatives, and straight-chain aliphatic compounds. The latter ones can be more effectively oxidized in the presence of silver sulfate as catalyst. In the open reflux methods, volatile organic compounds can also get lost. The most common interferences are the halides, bromide and iodide, and especially chloride ions. They can form insoluble silver halides and by this inactivate the catalytic effect of Agþ. In addition, under the strong oxidative conditions of the K2Cr2O7 reaction, they can be transferred to the elements and beyond that to halo-oxoacids and their ions and by this false positive results are produced. Due to the complex reactions and the undefined mixture of resulting products, a correction of the results based on simple theoretical considerations is not possible. The addition of mercury sulfate (HgSO4) before boiling which leads to a close to complete complexation of the halides can eliminate the problem to a great extent. However, in the case of halide concentrations r(X)42 g l1, the method fails. Saline water samples can be pretreated by evaporation of the hydrogen-halide acids at reduced pressure. The hydrogen-halide acids are produced by addition of concentrated sulfuric acid to the sample under rigorous agitation:

2 X  þ 2 H þ þ SO4 2 2SO4 2 k þ 2HXm

ð7Þ

Nitrite (NO2  ) exerts about 1 mg O2 per mg NO2  – N. Due to the low NO2  concentrations in most waters, this can mostly be ignored.

3.01.4.2.4 Applications The COD is well suited for the characterization of fairly polluted waters. Municipal wastewater consumes O2 in the range from 300 to 1000 mg l1. After biological treatment, the COD (O2) drops to 20–1000 mg l1. Landfill leachate can reach up to r(O2) of 3000 mg l1. The COD of surface water normally ranges from 5 to 20 mg l1 .The COD as standardized method has found its way into wastewater legislation. In Germany, for example, 50 kg is the COD unit for payment of fees (1 unit B36 h) for the direct discharge of wastewater into the aquatic environment, and the threshold amount of discharge is 20 mg l1 of 250 kg yr1. The environmental hazards of Agþ, Cr(VI), and Hg2þ used in the COD determination ask for methods which work with smaller volumes or for alternative clean methods. From this point of view, TOC (DOC) is a promising parameter for replacing COD. COD for quantitative determination of oxidizable OC does not necessarily lead to the equivalent result as TOC (DOC) measurements, even though in both cases the end product of the reactions is CO2. The simple approximation that one mass unit of COD(O2) equals one mass unit of TOC or DOC is not precise enough in most cases due to the different oxidation

13

states of the averaged carbon (DOC, TOC) in the organic load which consequently leads to different consumptions of oxidant and hence COD values. (see also Chapter 3.16 Chemical Basis for Water Technology). The O/C atomic ratios for moderately polluted rivers (e.g., Rhine, Main, Danube, and Elbe) are around 2 ranging from 1.3 to 2.7. For wastewater, the ratios are similar or a bit higher (Zanke and Ho¨pner, 1982).

3.01.4.3 PMC and Permanganate Index (IMn) 3.01.4.3.1 Background Potassium permanganate (KMnO4) is a fairly strong oxidizing agent. Therefore, it has been used as analytical tool to characterize dissolved organic water constituents. The oxidation method has been established as fairly simple wet chemical procedure since the early days of water-quality assessment. The method should be used as operationally defined determination of the oxidizability of relatively clean water samples. The results mostly do not allow a clear correlation with the OC content of the samples. The PMC is defined to be the amount of permanganate that reacts with the sample under defined conditions. The oxidative function of permanganate in acid medium (sulfuric acid) is given in Equation (8) and shows a standard potential of E0 ¼1.52 V:

MnO4  þ 5e þ 8H3 Oþ -Mn2þ þ 12H2 O

ð8Þ

3.01.4.3.2 Analytical procedure The redox reaction partners are the oxidizable organic substances which are mostly the aim of quantification. However, inorganic water constituents (e.g., Fe2þ, Mn2þ, Cl, or NH4 þ ) which can be oxidized have to be considered. According to the protocol (DIN EN ISO 8467, 1995; (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment)), the sample (defined volume) is mixed with sulfuric acid and the well-defined potassium permanganate solution, and the mix is heated for 10 min. Then a defined amount of sodium oxalate (Na2C2O4) is added in excess for reduction of the unreacted MnO4  , and the remaining oxalate is quantified (Figure 9). From all this, the amount of MnO4  consumed by the sample can be calculated, and from that the resulting oxygen demand is deduced:

rðKMnO4 Þ in mg l1  3:95 rðO2 Þ in mg l1

ð9Þ

The IMn is calculated according to

IMn ¼ f ðV1  V0 Þ=V2 M ¼ 16ðV1  V0 Þ=ðV2 Þ

ð10Þ

where V1 is the volume (in ml) of consumed permanganate solution of the sample; V0 the volume (in ml) of consumed permanganate standard solution of the blank solution; V2 the volume (in ml) of the consumed permanganate standard solution of the blank solution after addition of oxalic acid; and f (16 mg mmol1) the equivalence coefficient for the conversion into oxygen. The method is applicable to samples with r(O2)41 mg l1.

14

Sum Parameters: Potential and Limitations

KMnO4 (2 mmol l−1)

H2SO4 (2 mol l−1) 5 ml Aqueous sample 25 ml

Stirring heating in boiling water bath

Hot titration Waste 30 min pale rose

10 min reaction

Na2C2O4 (5 mmol l−1) 5 ml

KMnO4 (2 mmol l−1) 5 ml

Calculated result

Figure 9 Laboratory procedure for the determination of the permanganate consumption.

3.01.4.3.3 Interferences As far as PMC is used as surrogate parameter for OC, pitfalls resulting from the presence of oxidizable inorganic water constituents have to be considered. Halide concentrations, for example, r(Cl) 4300 mg l1, can cause significant errors leading to higher values due to the complex redox reactions of the halogen species. Fe2þ can also lead to positive false results which, however, can be corrected according to

rðFe 2þ Þ ¼ 1 mg l 1  rðKMnO4 Þ ¼ 0:57 mg l1

ð11Þ

In addition, there is a risk that aqueous KMnO4 solutions can decompose, especially at elevated temperatures. Recalibration and determination of blanks are, therefore, crucial. Another important aspect is the limited oxidation potential of KMnO4 solutions which results in only partial oxidation of OM, mostly of up to 40%.

3.01.4.3.4 Applications The IMn is mainly used for the assessment of drinking water, surface water, groundwater, and bottled water. Wastewater and other polluted waters need dilution before determination. The range for application is 0.5 mg l1or(O2)o10 mg l1. It is also suited for waters with r(Cl)o300 mg l1. Many pitfalls, the often poor yields in the oxidation of OM, and the often lacking reproducibility of the results have brought the parameter to a questionable reputation, and therefore it practically plays no major role in modern water assessment. Due to the large amount of available data of PMC from the old days, however, there might be some interest in comparison to longterm trends in water quality reflected in the oxidizability. The range of application reaches from around 1 mg l1 (as O2 equivalent) to several hundreds of mg l1. The EU directive for drinking water states 5 mg l1 as maximum parameter for oxidizability and recommends 2 mg l1. (see also Chapter 3.16 Chemical Basis for Water Technology).

3.01.4.4 Biochemical Oxygen Demand 3.01.4.4.1 Background Sustainable water management includes treatment of used water. Technical wastewater-treatment systems have been

developed for this purpose. From an economical and ecological point of view, it is most attractive to use microbiological methods (Wagner, 1979). Their application can be optimized with the help of parameters suited for the assessment of wastewater and for the control of the performance of the treatment units and the secondary effluents. Closely connected to the task of quantifying biodegradability, there is the aspect of the time frame, for example, the question: how long does it take to degrade a specific amount of OM? The time window may reach from several hours and a few days (poorly biodegradable  refractory) to even several years (practically nonbiodegradable). This poor precision asks for a pragmatically defined approach to reach meaningful results. Even though the ordinary oxygen from the air has only a standard potential of þ 0.82 V and hence is a relatively weak oxdidant (Equation (12)) at ambient temperature, with the help of biocatalysis the BOD is turned out to be a powerful parameter to serve the needs of a valuable assessment. Several standardized laboratory procedures have been developed on the basis of the O2 consumption of OM and inorganic compounds such as Fe2þ, sulfides, or reduced nitrogen compounds during a specified period of incubation with a mixed microbial population. Mostly, the procedure is focused on the organic load (carbonaceous BOD, OM):

O 2 + 4H 3 O + + 4e− OM + O 2

Bacteria

pH = 7

6H 2 O

CO 2 + H2 O + biomass

ð12Þ ð13Þ

3.01.4.4.2 Analytical procedure Standard methods are available for the determination of BOD (DIN EN 1899-1, 1998; ISO 5815:1989; Standard Methods 5210 B, 5210 C, 5210 D, 2005; (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment)). The BOD is mostly determined for an incubation period of 5 days (BOD5), but other incubation periods (1–50 days) can also be applied. The principle of the procedure is given in Figure 10. The air-saturated sample (if necessary seeded and/or diluted) is filled to overflow in a then airtight corked bottle of specified volume. Dissolved oxygen (DO) is measured immediately and after incubation of 5 days at 2073 1C. BOD5 is

Sum Parameters: Potential and Limitations

15

Defined dilution water

Glass bottle (e.g., 300 ml)

Aqueous sample (air saturated)

At start time After n days

O2 determination

Waste

7.0 < pH < 7.2 20 ± 3 °C

Seed suspension if needed

Nitrification inhibitor if needed

Figure 10 Experimental procedure for the determination of the BOD of aqueous samples.

calculated as concentration difference of the initial DO and the end DO. In case the oxygen consumption should exclude the demand of reduced nitrogen compounds (nitrogenous demand; e.g., ammonia and organic nitrogen), a nitrification inhibitor (e.g., 2-chloro-6-(trichloromethyl)pyrodine, TCMP, or allylthiourea (ATU)) has to be added. The DO determination is done either iodometrically (azide modification) or electrochemically by a membrane O2-electrode.

3.01.4.4.3 Interferences At the end, a proper BOD determination needs a residual concentration of oxygen of at least 2 mg l1. Water samples with high loads of OM can be measured after dilution. In case the water to be determined has a poor bacterial population, seeding is necessary. For that 0.5 ml sedimented municipal wastewater, B2 ml of biodegraded wastewater, or 5–10 ml river water are suited. The BOD of these additions has to be considered as blank. In case plankton is present, elevated BOD values have to be expected. The same applies for other O2-consuming water constituents such as Fe2þ, SO3 2 , and/or H2S/HS. A major problem for the BOD determination is the presence of poisonous or inhibiting substances (CN, CrO4 2 , Cu2þ, Hg(0, I, II), etc.) which might be overcome by dilution. In wastewater, nitrification may also lead to interferences. In order to avoid this, the addition of N-ATU to concentrations of 2–5 mg l1 is recommended. However, in this case O2 determination using the Winkler method becomes questionable. Many of the possible pitfalls can be diagnosed by online determination of O2 over the whole observation period (Figure 11).

3.01.4.4.4 Applications The method is well suited for the characterization of samples from rivers, lakes, estuaries, and wastewaters, and for their treatment efficiency in plants and effluents. BOD5 values normally range from 5 mg l1or(O2)o 250 mg l1. Other variations with shorter or longer incubation times than 5 days exist to measure rates of oxygen uptake. In special cases, incubation times of up to 90 days are used to determine the socalled ultimate BOD. Continuous oxygen monitoring (e.g., by

O2 electrodes) allow the characterization of different phases of biodegradation over time. The domain of BOD determinations consists of the wastewater and samples from its biological treatment. Typical municipal wastewater BOD5 lies around 60 g per capita equivalent. An average daily water use of 150–200 l per capita results in BOD5 concentrations of o25 and 300–350 mg l1 in treated and untreated wastewater, respectively. With respect to the changing biodegradability of wastewater constituents, it is interesting to relate the chemical oxidizability to the biochemical one, that is, to use the COD/BOD ratio for assessment (Leithe, 1971) (Table 4).

3.01.4.4.5 Related parameters (AOC) Another approach to quantify the biodegradability of OM uses the growth effect of a mixed population. After sterile filtration through a 0.2-mm nucleopore membrane, 275 ml of the water sample together with 25 ml of a sterile filtered merely inorganic nutrient solution is filled into a cuvette. The mixed population of bacteria retained by the 0.2-mm membrane filter is washed by NaCl solution and added to the mixed solution in the cuvette to reach a turbidity of 0.03 ppm SiO2 equivalents. The turbidity is measured as 121 forward scattering of a visual light beam in 30 min intervals for 60 h. The function of the relative turbidity over time gives the growth curve. Based on the assumption that the turbidity reflects the growth of the microbial population which is caused by the nutritious effect of the sample’s OM, it is attractive to relate the change of turbidity to the amount of assimilable carbon. The function of the relative turbidity over time gives the socalled growth curve (Figure 12). For the evaluation of the growth curve, the growth rate (GR; Equation (14)) and the growth factor (GF; Equation (15)) can be determined (Hambsch et al., 1992):

GR ¼

d lnðturbÞ at t ¼ tw dt

ð14Þ

turbðmaxÞ turbðstartÞ

ð15Þ

GF ¼

16

Sum Parameters: Potential and Limitations

O2-consumption (mg l−1)

35 30

d

25

c b

20 15 10 5 0

a

−5 0

2

4

6

8

10

12

14

16

Time, t (days) Figure 11 Typical O2-concentration curves for BOD determination (a: no biological degradation; b: biological degradation with lag phase; c, d: biological degradation without lag phase).

Table 4 COD/BOD ratios for the assessment of the removal efficiency of organic compounds by biochemical degradation COD/BOD

Assessment

o1.7

Organic substances show high biodegradation and mineralization Chemical degradation is insufficient due to – slow adaption of the bacteria – high amount of persistent compounds – inhibition of the reaction because of toxic substances No or practically no chemical degradation due to – persistent substances – inhibition of the reaction by highly toxic substances

1.7–10

410

where GR is the slope(s) at the inflection point of the curve for the exponential growth phase (tw). The steeper s the better assimilable the organic substances, for example, the GR gives information on the quality of the assimilable carbon. The ratio of the maximal turbidity and the initial turbidity (GF) is related to the quantity of assimilable carbon. From the shape of the curves inhibition and retardation, for example, by toxic water constituents, of the assimilation, for example, in the presence of recalcitrant fractions, can also be deduced. Figure 13 shows the growth curves for a lake water sample without and after treatment with different amounts of hydrogen peroxide (H2O2). It is obvious that in the original water sample, assimilation starts at the earliest. After about 15 h there is still a significant but slowly increasing turbidity possibly due to refractory OM. Oxidation with H2O2 (initial concentration r0(H2O2) ¼ 0.2 mg l1) leads to an increased lag phase in the assimilation of about 10 h followed by a steep exponential growth phase and finally, after 25 h, to a quite constant maximum turbidity; this reflects the higher amount

of assimilable carbon after chemical oxidation compared to the matter in the original sample. Tenfold initial H2O2 concentration leads to a further increased lag phase possibly due to the toxic effect of H2O2. The exponential growth phase shows a similar GR as the original lake water, and after 30 h a gradual increase of turbidity occurs up to 50 h which was the end of turbidity monitoring. From the gradual increase, an ongoing oxidative degradation of the organic substances to better assimilable ones can be deduced.

3.01.4.5 Interdependences There is a large amount of data on the load of OM in aquatic samples (Table 5). Despite the prosperous situation of available data, there are not too many reliable correlations between the different parameters. It might be relatively simple for defined model compounds but the complex mixture of realistic aquatic systems is difficult to assess, even though there are some reliable data for municipal wastewater (Table 6), and for drinking water and surface water (Leithe, 1971).

3.01.5 UVA and Visible Range Absorbance 3.01.5.1 Background Aquatic systems with high concentrations of OM, for example, bog lakes and organically rich aquifers, show a typical yellow to brown color. The absorption spectra for NOM samples in the UV (UVA) and visible range (VIA) are poorly resolved with a characteristic strong increase of the absorbance to lower wavelengths. This is typical for complex mixtures of substances with significant amounts of unsaturated bonds, lone pair electrons, and/or aromatic structures (Langhals et al., 2000). In addition, strong intermolecular interactions can add to

Sum Parameters: Potential and Limitations

17

Sample preparation Water sample

Sterile filtration

Cuvette

Inoculum

0.2 µm Nucleopore

275 ml of the sterile filtered sample

Mixed population of bacteria, washed from the sterile filters by NaCl solution

25 ml of a sterile filtered nutrient salt solution Registration of the growth curve Cuvette

Turbidity

Addition of inoculum until turbidity is 0.03 ppm SiO2

Measurement

Additional measures

(12° forward scattering) 60 h, every 30 min

Dissolved organic carbon (DOC) Total cell number (TCN) at the start and at the end

Evaluation of the growth curve Growth rate

Rel. turb.

Growth factor

(in the exponential phase tw) tW

GR = d ln(turb) dt

Time (h)

t = tw

GF =

turb(max) turb(start)

Figure 12 Procedure for the turbidimetric quantification of the AOC.

Turbity (12° forward scattering)

1.2 1 0.8 0.6 Original sample

0.4

Addition of (H2O2) = 0.2 mg l−1 0.2

Addition of (H2O2) = 2 mg l−1

0 0

10

20

30

40

50

Time, t (h) Figure 13 Typical growth curves for the organic carbon in lake water without and after addition of hydrogenperoxide (H2O2).

UV–Vis absorbance. Figure 14 shows two examples of typical UVA and VIA spectra of aquatic samples. This is the basis for using UV–Vis range information as surrogate parameter for a rough estimation of the dissolved OC concentration. It is quite common to use l ¼ 254 nm of the UV range and l ¼ 436 nm of the visible range for quantification. Around l ¼ 254 nm often a weak shoulder in the spectra is obvious which is assigned to chromophores with conjugated CQC and CQO double bonds.

According to Lambert–Beer’s law spectral absorbance is proportional to the concentration of the analyte:

AðlÞ ¼ kðlÞcd

ð16Þ

AðlÞ ¼ SAKðlÞd

ð17Þ

where A(l) is the absorbance at wavelength l; k(l) the molar absorption coefficient, in l (mol m)1 or l (g m)1; c the

18

Sum Parameters: Potential and Limitations

Table 5

Typical ranges for the content of organic matter in aquatic systems as reflected in sum parameters

Type of water

DOC, r(C) (mg l1)

Drinking water Groundwater Surface water Mesotrophic Eutrophic Municipal Wastewater Treated Landfill leachate

o2 0.5–4

COD, r(O2) (mg l1)

KMnO4, r(O2) (mg l1)

BOD5, r(O2) (mg l1)

o5 3–8 5–20

2–5 4–10

20–35 100–150

200 o25 4500

300–1000 20–100 o3000

AOC, r(Ac-C)a (mg l1)

AOX, r(Cl) (mg l1)

9–20 o80

30 50–80

6

250 20 200–13 000

o500 4500

a

Acetate-C calibrated.

Table 6 Transfer factors (A:B) for the values of sum parameters in wastewater assessment (Koppe and Stozek, 1990) Parameter B

KMnO4 COD BOD5 TOC

Parameter (A) KMnO4

COD

BOD5

TOC

1.0 0.6 1.4 2.0

1.6 1.0 2.2 3.1

0.7 0.5 1.0 1.5

0.5 0.3 0.7 1.0

concentration in mol l1 or g l1; d the path length, for example, of cuvette in m; and SAK(l) the spectral absorption coefficient in m1.

3.01.5.2 Analytical Procedure According to standard methods color (VIA) is determined by visual comparison of the sample with known concentrations of colored solutions (Standard Methods 2120 B, 2005) and as spectrophotometric method using l ¼ 436 nm (Standard Methods 2120 C, 2005; DIN EN ISO 7887 C1, 1994; (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment). The measurement of the color is either performed in Nessler tubes by looking vertically downward through the tubes (Standard Methods 2120 B, 2005) or by spectrophotometric determination at a wavelength between l ¼ 450 and 465 nm (Standard Methods 2120 C, 2005). The color unit (CU) of 500 is related to a mixture of 1.246 g potassium chloroplatinate and 1 g cobaltous chloride in 100 ml HCl conc. and diluted to 1000 ml. As a consequence, the unit of color equals 1 mg l1 platinum (in the form of chloroplatinate ions). Calibrated glass color disks are also used for comparison. The platinum–cobalt method is applicable to natural water, drinking water, and wastewater. A special advantage of the determination of samples in Nessler tubes is the relatively long optical pathway in the tubes which leads according to Lambert–Beer’s law to low limits of determination. Besides this method, the spectral absorption at l ¼ 436 nm can be used to determine the color (DIN EN ISO 7887 C1, 1994). Here, results are given as absorption coefficient in m1 (Standard Methods 5910 B, 2005; DIN 38404-3, 2005).

Based on the gradual decrease of absorbance with increasing wavelength, the value of l ¼ 254 nm is often used as fairly sensitive characteristic information on the content of UV-absorbing organic constituents. The results are given as absorption coefficients in m1. In addition to the described quite simple methods, more sophisticated methods for the determination of color have been standardized as well. There are the multi-wavelength method (Standard Methods 2120 D, 2005) and the tristimulus spectrophotometic method (Standard Methods 2120 E, 2005). Samples have to be filtered through 0.45-mm pore-size membranes to remove turbidity as the apparent color can be higher than the true color of the solution itself.

3.01.5.3 Interferences Interferences may arise from inorganic constituents, for example, ferrous iron, nitrate, nitrite, bromide, and from certain oxidants and reducing agents (e.g., ozone, chlorate, chlorite, and thiosulfate). An absorption scan between l ¼ 200 and 400 nm can be used to determine the presence of interferences. In addition, turbidity adds to the molecular spectrometric absorption in a complex way by absorption and light scattering. Reproducible results are obtained after a separation step is clear (o0.45 mm) solutions.

3.01.5.4 Applications Typical values for color determined at l ¼ 436 nm (SAK436) of different water samples are shown in Table 7. UV absorption is often used to monitor industrial wastewater effluents, and to evaluate the DOC removal during water-treatment processes. (see also Chapter 3.16 Chemical Basis for Water Technology, Chapter 3.15 Characterization Tools for Differentiating Natural Organic Matter from Effluent Organic Matter, Chapter 3.10 Online Monitoring Sensors). The spectral absorption exhibits a dependence on pH values with decreasing specific absorbance as solution pH decreases (Langhals et al., 2000). This reflects the different acid– base forms of the chromophores within the molecules or as suggested by Chen et al. (1977), an increase in molecular size due to macromolecular associations. The color caused by NOM also changes with the chemical characteristics of the

Sum Parameters: Potential and Limitations

19

3.5 Brown water (HO20) Wastewater effluent (Alb5)

3.0

Extinction

2.5 2.0 1.5

λ (254 nm)

1.0 λ (436 nm)

0.5 0.0 200

300

400

500

600

Wavelength,  (nm) Figure 14 UV and visible range spectra of a brown water lake sample (Hohlohsee, HO20) and a sample from the effluent of a biological wastewater treatment plant.

Table 7

SAK436 (VIA 436) values of different types of water

Type of water

SAK436 in (m1)

Tap water River water (moderately polluted) Brown water Wastewater Visual verification limit

o0.5 (recommended) 41 2–5 45 2

water. For example, NOM–metal complexes can be formed in the presence of Ca and Fe ions, and this affects the type and the intensity of the color. The relatively simple method of the determination at l ¼ 254 nm has led to its broad application as surrogate parameter for the more complicated instrumental determination of DOC. The correlation of the two parameters depends on the origin of the water sample but is quite constant for the individual aquatic systems which is demonstrated by the experimental data for the river Rhine (Figure 15). The values allow a rough characterization of the OM according to its genesis. The high sensitivity and consequently the small sample volume demand of the method is a significant advantage. This has led to a broad application of the method for the characterization of original samples from soils or water without major pretreatment and concentration procedures. Beyond that specific SAKs (SSAKs), for example, SAK values for r(DOC) ¼ 1 mg l1, can be used for a more detailed characterization and sound comparison of aquatic OM (Table 8). Many publications have become available on the UV and visible spectroscopic characterization, including luminescence of OM from natural origin (NOM) (e.g., MacCarthy and Rice, 1985; Cabaniss and Shuman, 1987; Bloom and Leenheer, 1989; Senesi et al., 1989; Hautala et al., 2000). They all prove

the comparability power and relevance of the SSAK in waterquality assessment.

3.01.6 Organically Bound Halogens Adsorbable on Activated Carbon (AOX) 3.01.6.1 Background Halogen-containing organic compounds are widely used in industrialized countries. Due to the resulting high amounts of production and the broad application as solvent and in many products, these anthropogenic halo-compounds have found their way into aquatic systems. Many of the compounds are of toxicological relevance for men and environment. Therefore, distribution and fate of the halo-compounds in nature and technical systems such as wastewater treatment plants are of major interest. A well-suited assessment parameter is a sum parameter reflecting all organically bound halogens which adsorb on activated carbon (AOX), where X ¼ Cl, Br, and I (Ku¨hn and Sontheimer, 1973). Similar parameters are dissolved organic halogens (DOX) or total organic halogens (TOX) which are often used synonymously to AOX.

3.01.6.2 Analytical Procedure The AOX procedure is based on the equilibration of PAC with the sample solution in batch mode (Ku¨hn and Sontheimer, 1973). Unwanted adsorption of common inorganic halides on PAC is reversed by competitive displacement by nitrate ions. After filtration of the loaded PAC, it is introduced into a furnace that pyrolyzes PAC and OC to CO2 and the bound halogens to hydrogen halides (HX). A carrier gas stream (mostly O2) transports the HX to a micro-coulometric titration cell. There the halides are quantified by measuring the current produced by silver-ion precipitation of the halides. In the cell, a constant silver-ion concentration is maintained from a solid silver electrode. The current for that is

20

Sum Parameters: Potential and Limitations 9.5

SAK (254 nm) (m−1)

8.5

Ludwigshafen km 421.4 l Mainz km 500.6 l

7.5

Koblenz km 588.3 l 6.5

Köln km 684.5 l

5.5

Düsseldorf km 732.1 r Wittlaer km 757.9 r

4.5

Basel-Birsfleden

3.5

Karlsruhe

2.5 1.5

2

2.5

3

Dissolved organic carbon (DOC) (g m−3) Figure 15 UVA and DOC concentrations of the river Rhine water (monthly composite samples from the river Rhine at different sampling places (stream km); l ¼ left, r ¼ right side; ARW, 2004; AWBR, 2006).

Table 8

Spectroscopic characteristics of selected original water and fulvic acid (FA) samples (Frimmel et al., 2002)

Water sample

Brown water lake Brunnsee Hohlohsee Brown water lake, fulvic acid HO14 FA (pH ¼ 2) HO14 FA (pH ¼ 7) HO14 FA (pH ¼ 11) River water (Rhine) Lake water (Lake Constance) Groundwater (high load of humic substances, Fuhrberg) Secondary effluent, Neureut Soil seepage water

proportional to the number of moles of halogens introduced by the carrier gas. Figure 16 gives an outline of the AOXdetermination procedure. The standardized version of the parameter method has also made its way into wastewater legislation in Germany (e.g., DIN EN ISO 9562, 2005; Standard Methods 5320 B, 2005). The determination of AOX in waters with high salt content can be preferably done with the help of solid-phase extraction (SPE), for example, with styrene–divinylbenzene copolymer. After rinsing the polymer phase with sodium nitrate solution, the AOX compounds are eluted with methanol, the methanol extract is diluted with water, and the ordinary AOX procedure using activated carbon is applied to the solution (DIN 3840922, 2001). Calibration can be done, for example, by 2,4,6-trichlorophenol. Forensic analysis may aim for a differentiation of the halogens. The appearance of iodinated X-ray contrast media in aquatic systems (Putschew et al., 2000) or the formation of organically bound bromine in the course of oxidative water treatment (Tercero and Frimmel, 2008) are prominent examples where halogen-specific AOX can help to determine the distribution and to investigate the fate of the

SAK254/DOC (l (mg m)1)

SAK436/DOC (l (mg m)1)

SAK254 /SAK436

4.50 5.09

0.42 0.30

10.6 13.2

4.80 4.98 5.20 2.21 2.92 2.92 1.44 3.13

0.30 0.38 0.58 0.12 0.09 0.15 0.10 0.18

15.9 13.1 8.8 17.6 31.2 19.7 13.7 16.7

specific group of compounds. The analytical approach traps the AOX combustion gases containing the different HX molecules in an alkaline solution which then is analyzed for Cl, Br, and I by ion chromatography (Oleksy-Frenzel et al., 1995, 2000) or by atomic emission spectroscopy (OES-ICP) (Abbt-Braun et al., 2006).

3.01.6.3 Applications The standard method is applicable for samples with AOX concentrations of r(Cl)45 mg l1. Special care has to be taken for Cl-free PAC and highly pure chemicals. Blank determinations are mandatory. The Cl content of virgin PAC should not exceed r(Cl)o20 mg g1. According to the relatively low detection limit, the method can be applied to a broad range of aquatic samples, including drinking water, process water, wastewater, and water from different stages of water treatment and from the entire aquatic environment. Due to its broad applicability and ecological relevance, the parameter has found its way into water legislation and into many assessment protocols for wastewater, treatment plant effluents, and rivers and lakes. In addition to the classical AOX determination

Sum Parameters: Potential and Limitations

Aqueous sample (100 ml)

21

Discard filtrate

Adsorption batch (50 mg PAC)

Equilibration

Filtration (0.4 μm polycarbonate filter)

Washing (nitrate solution)

h

ICP-AES ICP-MS Cl−, Br−, I− determination

Microcoulometric titration of Σ(Cl−, Br−, J−)

Ionchromatographic Cl−, Br−, I− determination or

PAC combustion (in O2 gas 950 °C)

HXabsorption (75% acidic acid; 20 mmol l−1 (NH4)2CO3)

Alternatively Figure 16 Experimental procedure for the determination of adsorbable organic halogen and the amounts of the different halogen species.

which includes most of the organic halogen compounds, there is the possibility to quantify specific fractions. (see also Chapter 3.16 Chemical Basis for Water Technology, Chapter 3.15 Characterization Tools for Differentiating Natural Organic Matter from Effluent Organic Matter). Recently on several occasions, elevated iodinated AOX concentrations were found in aquatic systems. The family of poorly biodegradable iodinated X-ray contrast media which has been broadly applied in medical diagnosis is the reason for that (Ternes and Hirsch, 2000; Putschew et al., 2000; AbbtBraun et al., 2006; Putschew and Jekel, 2006; Wolf et al., 2006). Data from sand column experiments (Table 9) run with contaminated wastewater reveal a partial elimination and/or degradation of the iodinated contrast media.

3.01.6.4 Related Parameters There is another approach for an integral determination and characterization of organic compounds containing halogens. The method is based on repeated liquid/liquid extraction of the aqueous sample with pentane, hexane, or heptane at a volume ratio of 20:1 (EOX, extractable organically bound halogens). The extract is dried and incinerated in a hydrogen oxygen flame. The mineralized products in the condensate are quantified with the help of volumetric precipitation analysis based on silver nitrate. In comparison to the AOX determination which can be found in wastewater legislation, the quantification of EOX is of lower importance possibly due to less reliable results (Sontheimer and Schnitzler, 1982; DIN 38409-8, 1984).

3.01.7 Additional Sum Parameters 3.01.7.1 Background There are several other sum parameters for water-quality assessment. They focus on either inorganic species such as pH,

Table 9

Iodine balance of column experiments (numbers in mg1)

I Species

Total iodine (ICP-MS) Iodine of X-ray compounds (HPLC) Inorganic iodide (IC-ICP-MS) AOI (iodinated organic metabolites) AOI-iodine of X-ray compounds

Influent aerobic

Effluent column 1 unsaturated

Effluent column 2 saturated

2.3470.04

2.4870.23

2.4370.14

2.3570.01

0.5570.06

1.5370.30

0.02070.003 1.6470.22

0.03770.012

2.2570.10

1.3870.09

2.2270.04

–0.1170.16

0.8270.13

0.6970.13

Glass columns (l ¼ 1.2 m, d ¼ 20 cm) filled with medium grain quartz sand. Feed: wastewater from the inflow of a municipal sewage treatment plant spiked with X-ray contrast media (Neureut/Karlsruhe, r(DOC) ¼ 30  90 mg l1). Conditions: waterunsaturated and water-saturated conditions (V E 2 l d1). Despite the complex and highly dynamic wastewater matrix, the example demonstrates clearly the valuable information on interdependences of the different organic and inorganic iodine species.

electrical conductivity, radioactivity or metals, (see also Chapter 3.03 Sources, Risks, and Mitigation of Radioactivity in Water, Chapter 3.02 Trace Metal(loid)s (As, Cd, Cu, Hg, Pb, PGE, Sb, and Zn) and Their Species) and they quantify organically bound hetero-elements or represent special types of organic compounds. Some of them reflect specific structural features, others are based on defined operations used for isolation or identification. A selection is given in Table 10. (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment).

22

Sum Parameters: Potential and Limitations

Table 10

Selection of additional sum parameters (see also Chapter 3.11 Standardized Methods for Water-Quality Assessment)

Targets (concentration range)

Method principle

Reference

Lignin and tannin Volatile organic acids (up to C6)

Folin phenol reagent, blue colour (a) Adsorption on silicic acid, elution with chloroform-butanol, titration with NaOH (b) Distillation, titration with NaOH (c) GC-FID 4-aminoantipyrine (a) After distillation (b) Chloroform extraction (c) Flow analysis

Box (1983) Westerhold (1963)

Phenols (1–250 mg l1)

Surfactants (0.2–2 mg l1 non-ionic) (40.1 mg l1 non-ionic) (40.01–0.2 mg l1 anionic) Aquatic humic substances Hydrocarbons, oil, and grease (o10 mg l1)

Nano- and microparticles Metal complexation capacity

Cholinesterase

Sublation (N2, ethylacetate) Methylene blue (MBAS) (in chloroform) Dragendorff reagent Cobalt thiocyanate (CTAS) (in methylene chloride) Adsorption/desorption on/from XAD (a) Gravimetric n-hexane/MTBE (extraction) (b) Extraction trichlorotrifluoroethane IR (c) Soxhlet extraction (for sediments) (d) Gravimetric (solid phase extraction) Flow-field-flow-fractionation (F4) (a) Polarographic Cu2þ titration (b) Metal selective electrode titration (c) Fluorescence Photometry

To differentiate between sum parameters and group parameters as it was suggested in the past (e.g., Sontheimer et al., 1986) seems to be idle since sum parameters in the modern sense do all allow an integrative view on well-defined aquatic water constituents without single compound (or even particle) identification. Of course, the precise definition of the individual sum parameter is most important to avoid misinterpretation of the results. As valuable tools for assessment and orientation, they are challenged by naturally occurring matter and emerging pollutants as well.

3.01.7.2 Examples for Emerging Parameters Four examples are given to briefly demonstrate the power of actual sum parameters’ development and their application in the assessment of aquatic samples. The given approaches are selected as typical examples of modern needs for information on the aquatic environment and its sustainable use and management. The first example focuses on the vital reservoir of refractory OM called humic substances (HSs), the second one addresses the colloids and the young world of nanoparticles (NPs) (see also Chapter 3.05 Natural Colloids and Manufactured Nanoparticles in Aquatic and Terrestrial Systems), the third one shows a typical impact of the availability of advanced instrumentation on the gross characterization of aquatic samples, and the fourth one helps to answer fundamental questions such as: What does it all matter? Is the determined amount dangerous? Which kind of bioeffect has to be watched?

3.01.7.2.1 Humic substances Aquatic humic substances (AHSs) consist of refractory OM ubiquitous in aquatic systems and can be isolated according to

Heukelekian and Kaplovsky (1949) Pavan et al. (2000) DIN 38409 (1984) Neufeld and Paladino (1985) Standard Methods 6420 B (2005) DIN EN ISO 14402 (1999) Schwuger (1996) Kunkel et al. (1977) Osburn (1986); DIN 38409 (1980) ISO 7875-2 (1984) Tabak and Bunch (1981) Frimmel et al. (2002) US-EPA (1998) Gruenfeld (1973) Ullmann and Sanderson (1959) US-EPA (1999) Von der Kammer and Fo¨rstner (1998); Delay et al. (2010) Lund et al. (1990) Tuschall and Brezonik (1983) Ryan and Weber (1982) Herzsprung et al. (1989)

standardized procedures recommended by the International Humic Substances Society (IHSS) (Thurman and Malcolm, 1981; Malcolm and MacCarthy, 1992; Leenheer and Croue´, 2003; IHSS, 2010). The principle of the methods is given in Figure 17 and allows to differentiate between fulvic acids (FAs) and humic acids (HAs) according to their pH-dependent solubility and adsorption/desorption on polymer resins. The procedure has opened the door for a better understanding of the occurrence and structure of AHS and their contribution to the DOM in the hydrosphere (Frimmel et al., 2002; Senesi et al., 2009). They are left over from organisms and the reservoir for new life. Their genesis and fate can now be compared for different regions and climatic zones. Based on OC concentrations, reliable balances can be made even on global scale. In addition, the multimethod approach with analytical instrumentation helps to elucidate the aquatic function and fate of operationally defined fractions.

3.01.7.2.2 NPs and colloids Colloids and particles (NPs) of the micro-scale have been recognized in the aquatic environment for quite some time (e.g., Frimmel et al., 2007). Recently, the broad application of engineered NPs (ENPs) in daily life has led to the concern of their role in the water cycle (Frimmel and Delay, 2010; (see also Chapter 3.05 Natural Colloids and Manufactured Nanoparticles in Aquatic and Terrestrial Systems)). For the assessment of the resulting heterogeneous systems, powerful methods are needed. Figure 18 shows an experimental setup which is suited to gain information, for example, on particle size distribution and the carrier function of particulate matter in aquatic samples (von der Kammer and Fo¨rstner, 1998;

Sum Parameters: Potential and Limitations

23

Aquatic sample (TOC/DOC 100%)

Filtration

0.45 μm

HCl pH ≤ 2 XAD-8 Dissolved nonhumic substances (NHS) (NHS; 30−50%) and inorganic ions

Penetration Adsorption NaOH 0.1 molar

Elution

Humic substances (HS; 20−60 %) HCl pH = 2 Precipitation Filtration >0.45 μm

Humic acids (HA; 5−20%)