Elsevier

Journal of Hazardous Materials

Volume 299, 15 December 2015, Pages 453-461
Journal of Hazardous Materials

Influence of co-substrate on textile wastewater treatment and microbial community changes in the anaerobic biological sulfate reduction process

https://doi.org/10.1016/j.jhazmat.2015.07.044Get rights and content

Highlights

  • Textile wastewater treatment performance was investigated with different co-substrates.

  • Dye biodegradation and biotransformation enhanced with lactate as co-substrate.

  • Sulfate removal significantly decreased under limited co-substrate concentration.

  • Changes in microbial community structure were studied using bar-coded pyrosequencing.

  • Lactate as co-substrate showed the highest relative abundance of sulfate reducing bacteria.

Abstract

This study investigated the anaerobic treatment of sulfate-rich synthetic textile wastewater in three sulfidogenic sequential batch reactors (SBRs). The experimental protocol was designed to examine the effect of three different co-substrates (lactate, glucose, and ethanol) and their concentrations on wastewater treatment performance. Sulfate reduction and dye degradation were improved when lactate and ethanol were used as electron donors, as compared with glucose. Moreover, under co-substrate limited concentrations, color, sulfate, and chemical oxygen demand (COD) removal efficiencies were declined. By reducing co-substrate COD gradually from 3000 to 500 mg/L, color removal efficiencies were decreased from 98.23% to 78.46%, 63.37%, and 69.10%, whereas, sulfate removal efficiencies were decreased from 98.42%, 82.35%, and 87.0%, to 30.27%, 21.50%, and 10.13%, for lactate, glucose, and ethanol fed reactors, respectively. Fourier transform infrared spectroscopy (FTIR) and total aromatic amine analysis revealed lactate to be a potential co-substrate for further biodegradation of intermediate metabolites formed after dye degradation. Pyrosequencing analysis showed that microbial community structure was significantly affected by the co-substrate. The reactor with lactate as co-substrate showed the highest relative abundance of sulfate reducing bacteria (SRBs), followed by ethanol, whereas the glucose-fed reactor showed the lowest relative abundance of SRB.

Introduction

Effluent from textile, paper and pulp industries are characterized by high organic content, dye, and sulfate concentrations that contribute chemical oxygen demand (COD), sulfate, and color [1]. Dyes and sulfates removal methods are becoming increasingly important in wastewater treatment because they can have many adverse effects on the environment. The presence of sulfate in wastewater is generally related to the acidification of natural water, with increases in salinity and hydrogen sulfide production resulting from anaerobic metabolism [2]. Textile dyes and their metabolic aromatic amines in wastewater streams have raised concerns owing to their severe impacts on human and aquatic health, since some of the dyes and their byproducts are carcinogenic and/or mutagenic, and can result in methemoglobinemia, liver, and kidney damage [3], [4], [5]. The adverse impact of these industrial effluents, including dissolved oxygen depletion in waterways (eutrophication), toxicity and esthetic effects of dyes, and sulfate induced salinity has demanded new and efficient removal methods for COD, dye, and sulfate from industrial wastewater [2], [6], [7].

The use of anaerobic biological processes for textile wastewater treatment are attractive owing to their low cost and efficient treatment performance for the integrated removal of different pollutants [5], [6], [7], [8], [9]. Sulfate-reducing bacteria (SRBs) are of great ecological importance in the biodegradation of organic matter and sulfate reduction in anaerobic environments [10]. Recently, researchers have investigated the use of anaerobic biological sulfate reduction processes for the integrated removal of azo dyes and sulfate-rich wastewater streams [11], [12], [13]. In anaerobic biological wastewater treatment, azo dye decolorization starts with azo bond reduction by suitable electron donors to form colorless aromatic amines. Moreover, the biogenic sulfide produced after sulfate anaerobic metabolism can be used as an electron donar in anaerobic environments, thereby leading to the reduction of dye chromophore systems and color removal [14], [15]. Owing to the synergetic action of sulfide and organics as electron donors, the anaerobic sulfate reduction process could be more efficient in azo dye degradation when compared with its anaerobic acedogenic or methanogenic counterparts.

Azo dye decolorization and sulfate reduction are both oxidation–reduction reactions, in which both sulfate and azo dye act as electron acceptors. The biological reduction of sulfate to sulfide theoretically requires eight reducing equivalents, i.e., a minimum COD/sulfate ratio of 0.67 is required for achieving a possible removal of sulfate [16], whereas reductive cleavage of a single azo bond requires four electrons. Thus, the availability of suitable and sufficient electron donors is a prerequisite for the efficient removal of sulfate and azo dyes, and the choice of electron donors has an important impact on sulfate reduction rates. Cao et al. recently investigated the influence of simple electron donors like organic acids, alcohols, and carbohydrates on the growth and activity of SRBs [17]. They reported formic acid as the most effective carbon and energy source for sulfate removal. The availability of specific electron donors may not only influence the activity of SRBs, but also that of dye decolorization and biodegradation. To date, only a few studies have investigated the dye biodegradation in sulfidogenic reactors, however there is still a lack of information about the impact of co-substrate on wastewater treatment performance and on sulfidogenic sludge microbial structure [11], [13]. We present here, for the first time, a systematic investigation of different co-substrates influence on textile wastewater treatment performance and microbial community structures in sequencing batch reactors (SBRs). The study provides new information about the potential of SRBs to treat recalcitrant textile wastewaters and trace the fate of dye and sulfate in substrate-limited environments. Total aromatic amines (TAA) analysis and FTIR spectroscopy were used to reveal the possible effects of co-substrate on dye biodegradation and biotransformation. To date, no information is available about the impact of co-substrate on microbial communities treating textile wastewater in sulfidogenic reactors. Therefore, bar-coded pyrosequencing was used to investigate the effect of co-substrate on bacterial communities in sulfidogenic reactors for treating synthetic textile wastewaters.

Section snippets

Sulfidogenic sludge culture and influent

The mixed culture of SRBs used in this study was enriched from anaerobic digester sludge, as described earlier [12], and was used to inoculate three sequencing batch reactors (SBRs). Postgate's B medium was used to prepare the active SRBs cultures in 1 L bottles at 35 °C on a rotary shaker at 110 rpm [18]. Sulfate reduction and sulfide production were indicated by blackening of the media. The composition of synthetic wastewater is given as (g/L): K2HPO4 0.50, NH4Cl 1.0, Na2SO4 1.20, FeSO4·7H2O

Dye decolorization and formation of aromatic amines

Fig. 1 depicts the dye removal efficiencies in all three reactors during the entire operation period. The results showed that dye removal efficiencies were very high for the three reactors, with more than 98.23% color removal in period 3, and no significant difference was observed among the three reactors. In period 4, when the dye concentration was increased from 100 to 200 mg/L, SBR2 (with glucose as co-substrate) showed a decrease in decolorization efficiency in the beginning of the period,

Conclusion

The present study investigated the role of co-substrates in anaerobic biological sulfate reduction processes treating textile wastewater. The experimental results determined the significance of co-substrate selection and the competition of sulfate and azo dye for electron donors under varying co-substrate concentrations. Sulfate reduction was promoted when lactate and ethanol were used as electron donors compared to glucose. Simultaneous organic sulfate and DR 80 removal can be achieved if

Acknowledgements

This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation (NRF) of Korea (NRF-2014H1C1A1066929). This study was also supported by grants (NRF-2013R1A1A4A01008000 and NRF-2009-0093819) through the ME and NRF of Korea. This research was also supported by the NRF grant by the Korea government (MSIP) (NRF-2015M2A7A1000194).

References (35)

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