WATER RESEARCH A Journal of the International Water Association
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w a t e r r e s e a r c h 4 5 ( 2 0 1 1 ) 1 5 1 9 e1 5 2 8
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Feasibility of a two-stage reduction/subsequent oxidation for treating Tetrabromobisphenol A in aqueous solutions Si Luo, Shao-gui Yang*, Cheng Sun*, Xiao-dong Wang State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China
article info
abstract
Article history:
A “two-stage reduction/subsequent oxidation” (T-SRO) process consists of FeeAg reduction
Received 3 July 2010
and Fenton-like oxidation under ultrasound (US) radiation. Due to the refractory oxidation
Received in revised form
of brominated flame retardant, T-SRO was employed to remove Tetrabromobisphenol
22 October 2010
A (TBBPA) by the combination of first debromination and succeeding oxidation. It indicated
Accepted 31 October 2010
that the T-SRO process resulted in a complete decrease in TBBPA concentration and
Available online 10 December 2010
a 99.2% decrease in BPA concentration. The T-SRO process for the removal of TBBPA is much effective than Fenton-like oxidation of TBBPA alone. The result showed that US
Keywords:
radiation improved the Fenton-like oxidation rate of BPA solutions. The addition of dis-
Two-stage
solved iron into the Fenton-like oxidation system could accelerate the first 2 min reaction,
Debromination
but had little effect on the following process. The main intermediate products resulting
Fenton-like oxidation
from TBBPA reduction and BPA oxidation were identified by GCeMS and LC-MS/MS. On the
Tetrabromobisphenol A
basis of this analysis, reactions with OH radical were identified as the major chemical
Bimetallic nanoparticles
pathways during BPA oxidation. ª 2010 Published by Elsevier Ltd.
Ultrasound radiation
1.
Introduction
Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardant around the world. It can be covalently bound to the polymer in the manufacturing process (de Wit, 2002). TBBPA and its dimethylated derivative have been detected in various environmental matrices, and they negatively affect various aspects of mammalian and human physiology (Sellstro¨m and Jansson, 1995; Helleday ¨ berg et al., 2002). Conseet al., 1999; Meerts et al., 2000; O quently, removal of TBBPA in the contaminated environment is necessary and significant. The reported treatment mainly includes biotransformation, photochemical transformations and thermal decomposition (Mackenzie and Kopinke, 1996; Barontini et al., 2004; Eriksson et al., 2004). In addition, it also indicated that removal of the halogen substituent is a key step in the degradation of halogenated aromatic compounds.
This may occur as an initial step via reductive, hydrolytic, or oxygenolytic mechanisms or may occur after ring cleavage at a later stage of degradation (Monserrate and Haggblom, 1997). Zero valent iron (ZVI) and bimetallic particles have been used for degradation of halogen-containing organic substance (Orth and Gillham, 1996; Cwiertny et al., 2006). In our previous work (Luo et al., 2010), we reported that TBBPA was reductively debrominated to bisphenol A (BPA) over FeeAg bimetallic nanoparticles under US radiation. However, it is well known that BPA exhibits estrogenic activity, which increases the proliferation rate of breast cancer cells and induces the acute toxicity to freshwater and marine species (Pulgar et al., 1998; Kaiser, 2000). Therefore, the debromination of TBBPA in FeeAg/US system is incomplete, BPA must be further degraded. An effective method for BPA mineralizing is the application of Fenton (Fenton-like) oxidation technologies (Go¨zmen et al., 2003; Ioan et al., 2007). On the other hand,
* Corresponding authors. Tel./fax: þ86 25 89680580. E-mail addresses:
[email protected] (S.-g. Yang),
[email protected] (C. Sun). 0043-1354/$ e see front matter ª 2010 Published by Elsevier Ltd. doi:10.1016/j.watres.2010.10.039
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w a t e r r e s e a r c h 4 5 ( 2 0 1 1 ) 1 5 1 9 e1 5 2 8
ZVI can be used to substitute ferrous salts in the Fenton-like oxidation, and it seems to have similar degradation rates to homogeneous ferrous catalyst. It has confirmed that phenol (Bremner et al., 2006) and 4-chlorophenol (Zhou et al., 2008) could be rapidly degraded in ZVI/H2O2 system. Since iron can reductively transform the electron-withdrawing moieties and render recalcitrant compounds more amenable to subsequent oxidation processes, several researchers presented the ZVI reduction for the pretreatment of wastewater (Mantha et al., 2001, 2002; Oh et al., 2005). Oh et al. (2003) reported the enhanced Fenton oxidation of TNT and RDX through pretreatment with ZVI. Thus, in consideration of the complete treatment of TBBPA, ZVI-based reductive debromination followed by Fenton-like oxidation is proposed, where FeeAg bimetallic nanoparticles are used to debrominate TBBPA because of its higher catalytic activity relative to ZVI. This paper evaluates the effectiveness and feasibility of a T-SRO treatment of TBBPA. Experiments are conducted to examine separately the performance of the FeeAg nanoparticles reductive and Fenton-like oxidative systems. The effect of US radiation in Fenton-like oxidation process is discussed; the influence of dissolved iron (ferrous and ferric ions) on the oxidation kinetics of ZVI/H2O2 system is also investigated. On the basis of identifying intermediate and final products, the reaction pathways are proposed.
2.
Experimental section
2.1.
Materials
2.3.
The reduction of TBBPA (5 mg L1) was conducted by FeeAg nanoparticles (0.8 g L1) under US radiation (40 kHz and 100 W). Debromination experiments were performed in a chamber as shown in Fig. SM-1 (a) attached in Supplemental Material (SM). The detailed procedure of reduction experiment was reported in the literature (Luo et al., 2010).
2.4.
2.2. Synthesis and characterization of FeeAg bimetallic nanoparticles FeeAg bimetallic nanoparticles with core-shell structure were synthesized by reductive deposition of Ag on ZVI nanoparticles as described in the literature (Luo et al., 2010). Various analytical techniques including XRD, XPS and XRF were used to characterize the fresh and reacted (after reduction process) FeeAg bimetallic samples. X-ray diffraction (XRD) analyses of the samples were performed using ˚ ). Switzerland ARL X’TRA X-ray diffractometer (l ¼ 1.5418 A The metal oxidation states and surface atomic composition of FeeAg samples was examined via X-ray photoelectron spectroscopy (XPS, Thermo VG Scientific ESCALAB 250). X-ray fluorescence (XRF, Switzerland ARL Corporation) was used to measure the mass of Ag deposited on the surface of nanoiron.
Fenton-like oxidation experiment
To keep a constant temperature (25 1 C), the Fenton-like process was conducted in a chamber as presented in Fig. SM-1 (b). The reduction and oxidation experiments were carried out in the same vessel. In each bottle, the solution contained BPA and FeeAg nanoparticles after reduction. Its initial pH was adjusted to 3.0 0.1 with 0.1 M H2SO4 and 0.1 M NaOH solutions. The oxidation experiments were started by dropping H2O2 solutions into the mixture by a separatory funnel. The flow rate was controlled at 2 mg L1 min1 and lasted 10 min in the whole oxidation process. At the given reaction time intervals, 1 mL sample was withdrawn. 10 mL 1 M tert-butanol was immediately added into the sample as reaction inhibitor. Then the samples were filtered by a syringe filled with a little silanized glass wool. The concentrations of BPA and intermediates in the filtrate were measured by high-performance liquid chromatography (HPLC). If no specific instructions are given, initial pH of Fenton-like oxidation is 3.0 0.1, nanoparticles loading is 0.8 g L1 and Ag content in FeeAg composite material is 1 wt.%.
2.5. Tetrabromobisphenol A, bisphenol A and tert-butanol were obtained from SigmaeAldrich Company. H2O2 (30%, v/v) was purchased from Fisher Company. AgCl, FeSO4$7H2O, Fe2(SO4)3, H2SO4, NaOH, Na2SO3, 1,10-phenanthroline and ferrous ammonium sulfate were provided by Nanjing Chemical Company. HPLC-grade methanol and dichloromethane were purchased from Tedian Company and used without further purification. Milli-Q water was used throughout this study. The zero valent iron used was iron powder (Shenzhen Junye Nano Material Co., Ltd, >99.9%, 24 mL)
(5)
2 - 0.5 kDa (22 -24 mL)
(4)
60%
7 - 3 kDa (20-22 mL)
(3)
40%
25 - 20kDa (17 – 18 mL)
(2)
20%
> 5000 kDa (8 mL)
(1)
80%
0%
B1
are equivalent to 412$106 C necator disrupted cells, which is liable to the release of 1.7 mg of cellular components per g of biofilm VSS. Comparing this amount with the amount of proteins and sugars measured in the soluble extracts indicates that the multi-method protocol did not induce significant cell breakage in B2 biofilm since the level of contamination of the extracted EPS by released cellular molecules was estimated to 0.8%. However, by performing similar determination for B3 biofilm extracts results indicate a higher level of intracellular compounds that was estimated as 9.7% of the total extracted sugars and proteins.
1000000
400
-100 0
a Total G6P-DH activity as the sum of the G6P-DH units measured in sonication, Tween and EDTA extracts. b Evaluated by measurement of the G6P-DH activity released after lysis of cupriavidus necator pure suspensions: 0.2 U per 106 equivalent lysed cells. c Evaluated using the correlation factor of dry biomass per number of cells: 4.08$106 g per 106 cupriavidus necator cells. d Released cellular compounds after extraction/total extracted proteins and sugars.
B1
Molecular weight (kDa)
B2 extract
1400
B2
Quantitative EPS distribution (% peak area)
a
B1 extract
A Absorbance (mAU).g VSS
Table 2 e Controls of cell lysis during the extraction performed on B1, B2 and B3 biofilm and evaluation of the related contamination level of the EPS extracts.
B2
B3
Fig. 4 e Global size distribution profiles at 280 nm of total EPS extracted from each B1, B2 and B3 biofilm (A) by size exclusion chromatography. Linear semi-logarithmic relation between molecular weight of standard proteins and elution volume (A, insert). Five different EPS size clusters (1 to 5) were identified between 0.5 kDa and 5000 kDa and their relative distribution inside each biofilm was evaluated by peak integration of the 280 nm signal (B).
by 3e7 kDa size molecules and (iii) a range of small size molecules eluted beyond 24 mL, which corresponds to the total inclusion volume of the column. These latter small fractions are not in the optimal separation range offered by the column but are expected to be under 0.5 kDa and are grouped in one single category. Fig. 4A also shows that these three recurring size fractions compose alone the B1 biofilm profile. On the other hand, additional peaks were identified in B2 and in B3 biofilm profiles. Indeed, both B2 and B3 biofilm profiles revealed a fraction eluted at 17e18 mL (i.e. 20e25 kDa), and B3 biofilm alone revealed a fraction eluted at 22e24 mL (i.e. 0.5e2 kDa). A total of five different size clusters were identified among the three studied biofilms: cluster 1 (>5000 kDa), cluster 2 (20e25 kDa), cluster 3 (3e7 kDa), cluster 4 (0.5e2 kDa) and cluster 5 (5000 kDa) is excluded from the column due to too high molecular weight EPS. Garnier et al. (2005) have already shown the existence of associated proteins/polysaccharides/mineral compounds in fractions eluted near the size exclusion volume when characterizing EPS extracted from activated sludge by SEC. Therefore, the EPS size cluster 1 might probably be represented by polymers eluted as a colloidal structure. Cluster 5 (