Enhanced azo dye wastewater treatment in a two-stage anaerobic system with Fe0 dosing

Bioresource Technology 121 (2012) 148–153

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Enhanced azo dye wastewater treatment in a two-stage anaerobic system with Fe0 dosing Yiwen Liu a,b, Yaobin Zhang a,⇑, Zhiqiang Zhao a, Yang Li a, Xie Quan a, Shuo Chen a a b

Key Laboratory of Industrial Ecology and Environmental Engineering, (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China Advanced Water Management Centre, Gehrmann Building, Research Road, The University of Queensland, St. Lucia, Queensland 4067, Australia

h i g h l i g h t s 0

" Fe dosing improved both COD and color removal in an acidogenic reactor. 0

" Fe increased fermentative bacteria responsible for acidogenesis and decolorization. 0

" Subsequent methanogenic performance was enhanced due to favorable feeding from Fe dosing.

a r t i c l e

i n f o

Article history: Received 13 April 2012 Received in revised form 30 May 2012 Accepted 1 June 2012 Available online 10 July 2012 Keywords: Anaerobic Fe0 Azo dye Fermentative bacteria

a b s t r a c t Azo dye wastewater treatment was enhanced in an acidogenic reactor (A1) by Fe0 dosing. Both COD (50%) and color (60%) removal in A1 were stable when the dye concentrations were increased from 200 to 800 mg/L. However, the performances of a Fe0-free control reactor (A2) showed low COD (34%) and color (32%) removals. The reason was attributed that Fe0 dosing enhanced the activity of fermentative bacteria, which played an important role in acidogenesis and decolorization. The methanogenic reactor fed with the effluent of A1 exhibited higher removal efficiency and treatment stability. These results suggested that Fe0 powder dosing was helpful to improve acidogenesis and decolorization to create a favorable feeding condition for the subsequent methanogenic treatment. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Azo dyes are the most common types of dyestuffs used in the textile industry and constitute about over 60% of total commercial dyes produced (Isik and Sponza, 2005; Manu and Chaudhari, 2002). Due to its toxicological effects, the discharge of azo dye wastewaters lead to serious threats to environmental system and public health, which have been extensively studied (Hassan et al., 2009). Conventional physicochemical treatment of azo dye wastewater, including absorption, coagulation, oxidation and electrochemical methods, has economical and technical limitations. Alternatively, biological processes are recognized as economical and environmentally friendly methods to remove dyes from wastewaters (Manu and Chaudhari, 2002). However, color removal under aerobic conditions is normally low (Alinsafi et al., 2006; dos Santos et al., 2007). On the other hand, anaerobic reduction of azo linkages (–N=N–) presents effective azo dye decolorization and becomes increasingly important (van der Zee and Villaverde,

⇑ Corresponding author. Tel.: +86 411 84706460; fax: +86 411 84706263. E-mail address: [email protected] (Y. Zhang). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.06.115

2005), and also is considered as the first step in azo dye biodegradation, in which colorless aromatic amines are formed. Since there are competition between anaerobic dye reduction and methanogenesis for the same electrons generated upon electron donor oxidation (dos Santos et al., 2006) and inhibition of azo dye on methanogens (Tan et al., 1999), a two-stage anaerobic system, in which acidogenic and methanogenic phases are separated, has been proposed to enhance the anaerobic decolorization (Firmino et al., 2010). In this system, the acidogenic reactor played a major role in azo dye reduction as compared with the following methanogenic reactor. However, the primary goal of this system is to enhance color removal rather than chemical oxygen demand (COD) removal. Therefore, corresponding strategies need to be made to improve COD removal efficiency in this system, especially in the first phase through optimizing acidogenesis, then providing valuable substrate for the following methanogenesis. Fe0, a cheap reductive metallic material, has been used in azo dye wastewater treatment (Nam and Tratnyek, 2000), but limited by its corrosion. A Fe0 packed anaerobic reactor for overcoming the rusting and helping to create an enhanced anaerobic environment for obligate anaerobes has been developed (Zhang et al., 2011a). It was found that not only the decolorization of azo dye

Y. Liu et al. / Bioresource Technology 121 (2012) 148–153

was promoted, but also methanogenesis (Karri et al., 2005) was enhanced and thus the COD removal was increased in this reactor (Liu et al., 2011a; Zhang et al., 2011a, 2011b) as compared to a control anaerobic reactor. As it is well-known, the successful operation of an anaerobic reactor depends on acidogenic bacteria and methanogenic archaea acting in harmony (Yu and Fang, 2003). It was assumed that Fe0 was also likely to enhance acidogenesis because iron acts as an electron donor in microbial metabolism and also improves a number of specific important enzyme activities in the acidification process. A previous study has demonstrated that Fe0 could significantly improve the COD removal and fermentation capacity in the acidogenic phase (Liu et al., 2012). Also, it has been indicated that fermentative bacteria played an important role in azo dye reductive process (dos Santos et al., 2006). Thus in the presence of Fe0, the fermentative bacteria will further promote the color and COD removal efficiency. Besides, reduction of azo dye by Fe0 could reduce the toxicity on anaerobic acidogenic microorganisms (Liu et al., 2011b). Therefore, it is likely that Fe0 could enhance both COD and color removal in acidogenic phase, and the favorable effluent from which could further facilitate the following methanogenic phase by providing less azo dye and organic pollutants but more valuable metabolic substrates such as acetate and butyrate. In the present study, Fe powder dosing in the acidogenesis stage for enhancing both anaerobic azo dye treatment as well as COD removal efficiency was investigated. To the best of knowledge, this could be the first attempt to improve anaerobic azo wastewater degradation by enhancing acidogenesis through Fe addition. 2. Methods 2.1. Experimental setup

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The hydraulic retention time (HRT) of A1 and A2 was 6 h. The HRT of M1 and M2 was fixed at 18 h. To mimic the temperature of practical works in the future scale-up, all reactors were operated at 15–20 °C. The concentrations of azo dye were increased from 200 to 800 mg/L, and the influent COD was fixed at about 3000 mg/L. 2.2. Sludge and wastewater The seed sludge obtained from a sedimentation tank in Chunliu municipal sewage plant in Dalian (China) was used as the seed sludge. After removing large debris, the ratio of volatile suspended sludge to total suspended sludge (VSS/TSS) was 0.74. The four reactors (i.e., A1, A2, M1 and M2) were inoculated with an initial TSS of 14.3 g/L. A1 and A2 (i.e., two acidogenic reactors) were fed with an artificial wastewater containing the azo dye Reactive Brilliant Red X-3B (X-3B in abbreviation, chemical name: 2,7-Naphthalenedisulfonic acid, 5-[(4,6-dichloro-1,3,5-triazin-2-yl) amino]-4-hydroxyl-3-(phenylazo)-, disodium salt, purity: 99%, molecular weight: 615.33 g/mol, purchased from Haicheng, China, with detailed chemical structure shown in Supporting information, Fig. S1), which is a typical azo dye widely used by textile industry in China. Sucrose, NH4Cl and KH2PO4 were added as the carbon, nitrogen, and phosphorus sources, respectively, to give a COD:N:P ratio of 200:5:1. Trace elements were added according to the following composition: 1 mL/L of a solution of a trace element solution containing Zn at 0.37 mmol/L, Mn at 2.5 mmol/L, Cu at 0.14 mmol/L, Co at 8.4 mmol/L, Ni at 0.25 mmol/L, H3BO3 at 0.8 mmol/L and EDTA at 3.4 mmol/L. The pH of the influent wastewater was buffered to 7 using NaHCO3 solution. 2.3. Analysis

0

Fe powder (40 g, Shenyang Chemical Reagent Factory, China, purity >98%, 0.2 mm in diameter, a BET surface area of 0.05 m2 g1) was dosed into the acidogenic reactor in a two-stage anaerobic system (Fig. 1). The acidogenic reactor (A1), operated in upflow mode, had a working volume of 2 L (u100  280 mm). The acidogenic effluent was fed into a methanogenic reactor (M1), also operated in upflow mode, which had a working volume of 6 L (u100 mm  900 mm). A control experiment was conducted in a similar two-stage anaerobic system. The control acidogenic reactor (A2) was the same as A1 but without Fe powder dosing. The control methanogenic reactor (M2) was identical to M1.

Fig. 1. Schematic diagram of the experimental system.

TSS, VSS and COD were determined according to Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The ORP was measured using an ORP combination class-body redox electrode (Sartorius PY-R01, Germany). The pH was recorded using a pH analyzer (Sartorius PB-20, Germany). Color was measured spectrophotometrically (Techcomp, UV-2301, Shanghai, China) at the dye’s wavelength of maximum absorbance (541.5 nm). The concentration of Fe (II) in the aqueous phase was determined by using ortho phenanthroline spectrophotometry (Techcomp, UV2301, Shanghai, China) according to Zhang et al. (2011a). Biogas collected from the methanogenic reactors was measured with a gas meter (Wet type gas meter, LMF-2, Changchun, China), after which its volume was calculated as standard temperature and pressure. The composition of biogas was analyzed by a gas chromatograph (Shimadzu, GC-14C/TCD, Japan). The concentrations of VFA, including acetate, propionate, butyrate, were determined using another GC (Shimadzu, GC-2010/FID, Japan) according to the method described by Jiang et al. (2007). The concentrations of VFA, including acetate, propionate, butyrate, were determined using another GC (Shimadzu, GC-2010/FID, Japan) according to the method reported by Yu and Fang (2001). Residual carbohydrate in the acidogenic effluent was determined by a sulfuric acid–anthrone method (Dubois et al., 1956). The concentration of total VFA (TVFA) in the effluent was quantified by using COD-equivalent concentration of main VFAs. The equivalent relationship between COD and substrates are as follows: 1.06 g COD/g carbohydrate, 1.07 g COD/g acetate, 1.51 g COD/g propionate and 1.82 g COD/g butyrate. The Mann–Whitney Rank Sum test was used to analyze the data. Fluorescence in situ hybridization (FISH) was used to determine the abundance of acidogens and acetogens in the acidogenic reactors. FISH was conducted according to the method described by Wu et al. (2001). Fluorescence labels of the oligonucleotide probes

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used in this study was EUB338 (Bacteria, GCTGCCTCCCGTAGGAGT, acidogens and acetogens) (Zhang et al., 2010). After hybridization, the specimens were stained with 40 ,60 -diamidino-2-phenylindole (DAPI). The samples were observed under a confocal laser scanning microscope (Leica SP2, Heidelberger, Germany). The FISH images obtained were imported to Image-Pro Plus 6.0 for analysis of the relative abundance of microorganisms.

3. Results 3.1. COD removal during acidogenesis under different influent dye concentrations Dye loading is an important operational factor which affects color and COD removal in the anaerobic process, increasing of which may negatively influence the anaerobic treatment due to toxic effects (van der Zee and Villaverde, 2005). After the acclimatization, to investigate the effects of dye loading on Fe powder enhanced acidogenesis, A1 and A2 were operated under stepwise increases in dye concentrations from 200 to 800 mg/L at a HRT of 6 h, with the influent COD fixed at about 3000 mg/L. As Fig. 2 shows, at a dye concentration of 200 mg/L, the COD removal of A1 was stable and averaged about 51%. Comparatively, the COD removal from A2 significantly declined from about 48% to 40%. As the dye loading increased to 400 and 600 mg/L, the COD removal for A1 and A2 remained around 51% and 38%, respectively. The COD removal of A1 decreased to 48% when the dye was increased to 800 mg/L; however, it recovered quickly and even achieved to 53% averagely. It is worth mentioning that, in spite of a sudden drop on COD removal after the dye concentration was increased, a fast recovery was found, which indicates that this system well adapted to the operational conditions. With respect to A2, the COD removal reduced to 34% at a dye concentration of 800 mg/L, indicating microbial inhibition by dye toxicity, which is in agreement with Bras et al. (2005), who also found a COD efficiency decreased from 92% to 67% when dye concentrations increased from 60 to 300 mg/L. A1 did not show this trend partially because zero valent iron (ZVI) could reduce the toxicity on anaerobic microorganisms (Liu et al., 2011b).These results clearly indicated that the COD removal in A1 was higher and more stable than that in A2, and A1 had a better resistance to increasing dye loadings.

3.2. Color removal during acidogenesis under different influent dye concentrations At the beginning, A1 and A2 showed relatively stable color removal at a dye concentration of 200 mg/L (shown in Fig. 3) averaging 60% for A1 and 50% for A2, respectively, which demonstrated important contribution of acidogenesis to the color removal process (Talarposhti et al., 2001). As the dye loadings were increased to 400 and 600 mg/L, the color removal of A2 obviously decreased to 38% and 33%, respectively, while that of A1 remained around 60%. When the dye loading was increased to 800 mg/L, the color removal of A1 still averaged 60%, but which of A2 was 32% averagely. The results of decolorization of A2 were in agreement with many studies (Bras et al., 2005; Isik and Sponza, 2005), in which color removal decreased after the dye concentration was increased. Especially, Firmino et al. (2010) also showed a decreased trend with a significant fluctuation in an acidogenic reactor of a conventional two-stage anaerobic system when treating dyes with increasing concentrations. However, a similar phenomenon was not observed in A1, which indicated that Fe powder dosing promoted the ability of the reactor to deal with increasing azo dye loading.

3.3. VFAs production during acidogenesis under different influent dye concentrations In the acidogenic stage, organic matters are mainly transformed into VFA, accompanied with the generation of CO2 and H2O. Fig. 4(a) summarized the TVFA concentration in the effluents of A1 and A2 under different influent dye concentrations. By increasing the dye loadings from 200 to 800 mg/L, the TVFA of both A1 and A2 were both stable, but the former was much higher than the latter, in agreement with the COD removal. Besides, the degree of acidification, defined as the ratio of COD-equivalent TVFA to the effluent COD (De la Rubia et al., 2009), could reflect more clearly the differences between the two reactors. From Fig. 4(b), at a dye concentration of 200 mg/L, the degree of acidification in A1 was 89.3%, meaning that most of the effluent COD were VFAs. Meanwhile, this degree in A2 was only 57.9%, indicating that more than 1/3 of the effluent COD was not acidified. Also, as the dye loadings increased to 800 mg/L, the degree of acidification in A2 dropped to only 48.6%. However, the degree of acidification in A1 only decreased slightly from 89.3% to 88.8% when the dye loadings changed from 200 to 800 mg/L.

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Fig. 2. COD removal of acidogenic reactors under different influent dye concentrations.

Fig. 3. Color removal of acidogenic reactors under different influent dye concentrations.

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Fig. 4. Acidogenic performances of A1 and A2 under different influent dye concentrations. (a) Effluent TVFA concentrations from A1 and A2 and (b) degree of acidification of A1 and A2. Error bars represent standard deviations of statistical analysis.

3.4. Overall performance of COD and color removal in two systems M1 and M2 were fed using the effluents from A1 and A2, respectively, for methanogenesis. The overall COD removal in A1 and M1 was more stable and reached 89–99% (Fig. 5a, Table 1), significantly higher than that in A2 and M2, which was only 75–95% and decreased obviously as the increasing dye loading. Also, methane production in M1 determined was 0.29 ± 0.02 L CH4/g CODremoved (STP), while that the methane production in M2 was 0.24 ± 0.01 L CH4/g CODremoved (STP).

(a) 100

The A1’s overall color removal was also stable and more than 95% (Fig. 5b, Table 1). These color removal efficiencies are better than those reported by Liu et al. (2011b) and Zhang et al. (2011a), who found less than 95% of X-3B (200–800 mg/L) decolorization by using an anaerobic zero valent iron packed reactor operated at a HRT of 24 h and COD of 3000 mg/L. However, the A2’s overall color removal decreased straightly from 95% to 80% when dye loading was increased, especially with a significant instability at a dye concentration of 800 mg/L. Similar results were also presented by Firmino et al. (2010), who reported the overall color removal efficiency of a conventional two-stage anaerobic reactor decreased from 77% to 61.2% when the dye concentration increased from 210 to 840 mg/L.

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4.1. Role of Fe0 in azo dye reduction dye (mg/L)

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Time (d) Fig. 5. Overall performance in two systems, respectively, (a) COD removal and (b) Color removal.

Clearly, the decolorization in A1 was higher and more stable than A2, due to the presence of Fe0. But direct degradation by Fe0 (chemical contribution of Fe0) might not have been the main pathway that caused high color removal in A1. The electrons provided by Fe0 (Fe02e = Fe2+, Fe2+ concentration in the reactor A1 averaged 20.4 mg/L) were 1.45 mmol e-equivalent, much lower than actual demand for increase of azo dye removal, i.e., 2.9 mmol e-equivalent at a dye concentration of 800 mg/L (dye concentration  reactor volume  removal difference between A1 and A2  available electrons of X-3B/molecular weight of X/3B, 0.8 g/L  2 L  (0.6–0.32)  4 mol/615.33 g/mol). Also, for 1.45 mmol e-equivalent provided by Fe0, the experiments carried out in the abiotic reactor with only Fe0 showed only 0.39 mmol e-equivalent was used for direct azo dye degradation. The electrons provided by Fe0 would be used for pH balance and potential microbial metabolism besides direct azo dye removal (Zhang et al., 2011a). This indicated that indirect azo dye removal enhanced by Fe0 (biological contribution of Fe0) such as increasing the activity of fermentative bacteria could play a significant role. Many studies (Chinwekitvanich et al., 2000; dos Santos et al., 2007, 2006; Firmino et al., 2010) have demonstrated that azo dye reduction by the anaerobic consortium was mainly carried out by fermentative bacteria. A previous work (Liu et al., 2012) has shown that Fe0 dosing could effectively improve the acidogenesis and activity of fermentative bacteria by lowering ORP and enhancing the activity of pyruvate–ferredoxin oxidoreductase (POR) which is a crucial enzyme in anaerobic acidification (Feng et al., 2009). Furthermore, more favorable fermentation process could promote

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Table 1 Overall performance in two systems. Dye concentration (mg/L)

A1 + M1

A2 + M2

COD removal (mg/L)

Color removal (mg/L)

COD removal (mg/L)

Color removal (mg/L)

200 400 600 800

96.64 ± 1.92 95.34 ± 0.85 94.26 ± 2.32 91.99 ± 1.96

96.38 ± 0.78 96.35 ± 0.58 96.89 ± 0.96 96.49 ± 0.72

93.27 ± 2.33 89.88 ± 1.20 85.49 ± 3.63 79.12 ± 2.71

94.38 ± 1.04 91.47 ± 0.76 91.10 ± 0.70 86.69 ± 3.30

the azo dye removal process. Therefore, in this situation, not only the COD removal process in A1 was efficiently enhanced (Fig. 2), but also the higher azo dye removal efficiency was observed in A1 (Fig. 3). 4.2. Role of Fe0 in acidogenesis The better performance of A1 in the COD removal was mainly attributed to the Fe powder dosing, which could enhance acidogenesis (Liu et al., 2012). Also, the results of VFA confirmed that A1 exhibited better acidogenic activity than A2, which played an important part in azo dye removal. It has also been reported that dyes may have an adverse influence on VFA production (Lee and Pavlostathis, 2004), which could be found in A2. In contrast, higher VFA production in A1 suggested that the fermentative bacteria in the Fe0 enhanced acidogenic rector did not show a significant inhibition, since Fe powder accelerated acidogenesis and promoted fermentative bacteria (Liu et al., 2012). In addition, Fe powder dosing could reduce the toxicity of high concentrations of azo dye on fermentative bacteria. The enhanced acidogenic bacteria could in return improve azo dye degradation. In addition, FISH test for the two acidogenic reactors could show the specific acidogenic microbial composition in both acidogenic reactors after the operation and the results are shown in Fig. S2. According to the analysis by Image-Pro Plus 6.0, the abundance of bacteria (acidogens and acetogens, red) in A1 was 88.3%, higher than that of 72.4% in A2, which is in agreement with the COD removal, degree of acidification and color removal in each acidification reactor. It is well-known that acidogens and acetogens are inclined to be obligate anaerobic bacteria. The greater amount of these bacteria in A1 was attributed to Fe dosing. More bacteria could increase the decomposition of organic matters into VFA. Also, these bacteria are capable of and responsible for decolorization of azo dyes (Bafana et al., 2008; Kalyani et al., 2008; Kolekar et al., 2008), hence A1 presenting better COD and color removal efficiencies. 4.3. Performance of the two systems The differences between the two systems (A1 + M1, A2 + M2) were related to the dye concentration as well as VFA composition from the effluent of acidogenic reactors. On one side, the effluent from A2 contained much more azo dye, which could further inhibit methanogenic activity in M2. Azo dye may have an inhibition effect on acetogenesis and methanogenesis and could result in specific VFA accumulation (Lee and Pavlostathis, 2004), i.e., propionate, accumulation of which is often observed in anaerobic reactor malfunctions (Hanaki et al., 1994a, 1994b) that will destroy the pH balance between acidogenesis and methanogenesis, further hindering methanogenesis from acetate. On the other side, the different VFA composition in the two reactors was also related to the reducibility of Fe powder. Fe0 could enhance the reductive environment and help maintain a relatively low ORP value in the anaerobic reactor (Liu et al., 2011a; Zhang

et al., 2011a), which can improve acetate and butyrate production (Liu et al., 2012). The percentage of acetate, butyrate and propionate in A1 averaged 40%, 23% and 37%, respectively, while it was 30%, 12% and 58% in A2, respectively (Supporting information, Fig. S3). The effluent from A1 containing more acetate and butyrate but less propionate was favorable for the subsequent anaerobic digestion in M1, including acetogenesis and methanogenesis. On the contrary, the higher percentage of propionate and inadequate acidification in the effluent of A2 retarded the subsequent methanogenesis in M2. As a result, the overall COD removal of A2 and M2 was lower than that in A1 and M1. It should be noticed that the color removal efficiency in methanogenic M2 was higher than acidogenic A2, which seemed contradictory to the fact that fermentative bacteria played a more important in color removal. Actually, it was likely because a substantial amount of fermentative bacteria lived in M2, and they could help to acetify the unfavorable effluent from A2 and thus reduced the azo dye (Fig. S3). 5. Conclusions A novel strategy for enhancing anaerobic azo dye wastewater treatment via Fe0 addition in the acidogenic phase of a two-stage anaerobic system was proposed. Both COD and color removal was improved by Fe0 dosing in this acidogenic reactor. Fe0 dosing effectively increased the activity of fermentative bacteria, which played an important role in acidogenesis and decolorization. Also, the overall performance of this two-stage system presented better treatment efficiency and stability. These results suggested that Fe0 dosing was helpful to improve acidogenesis and decolorization, and be used as a pretreatment method to create a favorable condition for the subsequent treatment. Acknowledgements This study was conducted with financial support from the National Basic Research Program of China (21177015), New Century Excellent Talent Program of the Ministry of Education of China (NCET-10-028), Fundamental Research Funds for the Central Universities of China (DUT11ZD108). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2012. 06.115. References Alinsafi, A., da Motta, M., Le Bonte, S., Pons, M.N., Benhammou, A., 2006. Effect of variability on the treatment of textile dyeing wastewater by activated sludge. Dyes Pigm. 69 (1–2), 31–39. APHA, 2005. Standard Methods for the Examination of Water and Wastewater. American Public Health Association, Washington.

Y. Liu et al. / Bioresource Technology 121 (2012) 148–153 Bafana, A., Chakrabarti, T., Krishnamurthi, K., Devi, S.S., 2008. Biodiversity and dye decolourization ability of an acclimatized textile sludge. Bioresour. Technol. 99 (11), 5094–5098. Bras, R., Gomes, A., Ferra, M.I., Pinheiro, H.M., Goncalves, I.C., 2005. Monoazo and diazo dye decolourisation studies in a methanogenic UASB reactor. J. Biotechnol. 115 (1), 57–66. Chinwekitvanich, S., Tuntoolvest, M., Panswad, T., 2000. Anaerobic decolorization of reactive dyebath effluents by a two-stage UASB system with tapioca as a cosubstrate. Water Res. 34 (8), 2223–2232. De la Rubia, M.A., Raposo, F., Rincon, B., Borja, R., 2009. Evaluation of the hydrolyticacidogenic step of a two-stage mesophilic anaerobic digestion process of sunflower oil cake. Bioresour. Technol. 100 (18), 4133–4138. dos Santos, A.B., Cervantes, F.J., van Lier, J.B., 2007. Review paper on current technologies for decolourisation of textile wastewaters: perspectives for anaerobic biotechnology. Bioresour. Technol. 98 (12), 2369–2385. dos Santos, A.B., de Madrid, M.P., de Bok, F.A.M., Stams, A.J.M., van Lier, J.B., Cervantes, F.J., 2006. The contribution of fermentative bacteria and methanogenic archaea to azo dye reduction by a thermophilic anaerobic consortium. Enzyme Microb. Technol. 39 (1), 38–46. Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A., Smith, F., 1956. Colorimetric method for determination of sugars and related substances. Anal. Chem. 28 (3), 350–356. Feng, L.Y., Chen, Y.G., Zheng, X., 2009. Enhancement of waste activated sludge protein conversion and volatile fatty acids accumulation during waste activated sludge anaerobic fermentation by carbohydrate substrate addition: the effect of pH. Environ. Sci. Technol. 43 (12), 4373–4380. Firmino, P.I.M., da Silva, M.E.R., Cervantes, F.J., dos Santos, A.B., 2010. Colour removal of dyes from synthetic and real textile wastewaters in one- and twostage anaerobic systems. Bioresour. Technol. 101 (20), 7773–7779. Hanaki, K., Hirunmasuwan, S., Matsuo, T., 1994a. Protection of methanogenic bacteria from low pH and toxic materials by immobilization using polyvinylalcohol. Water Res. 28 (4), 877–885. Hanaki, K., Hirunmasuwan, S., Matsuo, T., 1994b. Selective use of microorganisms in anaerobic treatment processes by application of immobilization. Water Res. 28 (4), 993–996. Hassan, S.S., Awwad, N.S., Aboterika, A.H., 2009. Removal of synthetic reactive dyes from textile wastewater by Sorel’s cement. J. Hazard. Mater. 162 (2–3), 994–999. Isik, M., Sponza, D.T., 2005. Effects of alkalinity and co-substrate on the performance of an upflow anaerobic sludge blanket (UASB) reactor through decolorization of Congo Red azo dye. Bioresour. Technol. 96 (5), 633–643. Jiang, S., Chen, Y.G., Zhou, Q., 2007. Effect of sodium dodecyl sulfate on waste activated sludge hydrolysis and acidification. Chem. Eng. J. 132 (1–3), 311–317. Kalyani, D.C., Patil, P.S., Jadhav, J.P., Govindwar, S.P., 2008. Biodegradation of reactive textile dye Red BLI by an isolated bacterium Pseudomonas sp. SUK1. Bioresour. Technol. 99 (11), 4635–4641. Karri, S., Sierra-Alvarez, R., Field, J.A., 2005. Zero valent iron as an electron-donor for methanogenesis and sulfate reduction in anaerobic sludge. Biotechnol. Bioeng. 92 (7), 810–819.

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Kolekar, Y.M., Pawar, S.P., Gawai, K.R., Lokhande, P.D., Shouche, Y.S., Kodam, K.M., 2008. Decolorization and degradation of Disperse Blue 79 and Acid Orange 10, by Bacillus fusiformis KMK5 isolated from the textile dye contaminated soil. Bioresour. Technol. 99 (18), 8999–9003. Lee, Y.H., Pavlostathis, S.G., 2004. Decolorization and toxicity of reactive anthraquinone textile dyes under methanogenic conditions. Water Res. 38 (7), 1838–1852. Liu, Y.W., Zhang, Y.B., Quan, X., Chen, S., Zhao, H.M., 2011a. Applying an electric field in a built-in zero valent iron – anaerobic reactor for enhancement of sludge granulation. Water Res. 45 (3), 1258–1266. Liu, Y.W., Zhang, Y.B., Quan, X., Li, Y., Zhao, Z.Q., Meng, X.S., Chen, S., 2012. Optimization of anaerobic acidogenesis by adding Fe0 powder to enhance anaerobic wastewater treatment. Chem. Eng. J., . Liu, Y.W., Zhang, Y.B., Quan, X., Zhang, J.X., Zhao, H.M., Chen, S.O., 2011b. Effects of an electric field and zero valent iron on anaerobic treatment of azo dye wastewater and microbial community structures. Bioresour. Technol. 102 (3), 2578–2584. Manu, B., Chaudhari, S., 2002. Anaerobic decolorisation of simulated textile wastewater containing azo dyes. Bioresour. Technol. 82 (3), 225–231. Nam, S., Tratnyek, P.G., 2000. Reduction of azo dyes with zero-valent iron. Water Res. 34 (6), 1837–1845. Talarposhti, A.M., Donnelly, T., Anderson, G.K., 2001. Colour removal from a simulated dye wastewater using a two-phase anaerobic packed bed reactor. Water Res. 35 (2), 425–432. Tan, N.C.G., Lettinga, G., Field, J.A., 1999. Reduction of the azo dye Mordant Orange 1 by methanogenic granular sludge exposed to oxygen. Bioresour. Technol. 67 (1), 35–42. van der Zee, F.P., Villaverde, S., 2005. Combined anaerobic-aerobic treatment of azo dyes – a short review of bioreactor studies. Water Res. 39 (8), 1425– 1440. Wu, J.H., Liu, W.T., Tseng, I.C., Cheng, S.S., 2001. Characterization of microbial consortia in a terephthalate-degrading anaerobic granular sludge system. Microbiology-UK 147, 373–382. Yu, H.Q., Fang, H.H., 2001. Acidification of mid- and high-strength dairy wastewaters. Water Res. 35 (15), 3697–3705. Yu, H.Q., Fang, H.H., 2003. Acidogenesis of gelatin-rich wastewater in an upflow anaerobic reactor: influence of pH and temperature. Water Res. 37 (1), 55– 66. Zhang, P., Chen, Y.G., Zhou, Q., Zheng, X., Zhu, X.Y., Zhao, Y.X., 2010. Understanding short-chain fatty acids accumulation enhanced in waste activated sludge alkaline fermentation: kinetics and microbiology. Environ. Sci. Technol. 44 (24), 9343–9348. Zhang, Y.B., Jing, Y.W., Quan, X., Liu, Y.W., Onu, P., 2011a. A built-in zero valent iron anaerobic reactor to enhance treatment of azo dye wastewater. Water Sci. Technol. 63 (4), 741–746. Zhang, Y.B., Jing, Y.W., Zhang, J.X., Sun, L.F., Quan, X., 2011b. Performance of a ZVIUASB reactor for azo dye wastewater treatment. J. Chem. Technol. Biotechnol. 86 (2), 199–204.