| Chloronitrobenzenes, as recalcitrant and toxic pollutants, have been declared to be priority pollutant by Environmental Protection Agency of USA, European Economic Community and China. Anaerobic-aerobic biological method is one of the most effective technologies for chloronitrobenzenes treatment. However, anaerobic degradation of chloronitrobenzenes is a rate-limiting step in the whole process due to the slow rate of microbial metabolism. In the present study,2,5-dichloronitrobenzene, which is generally used for the synthesis of dyes, was selected as a model compound. Effects of additional electron donors and redox mediator on anaerobic degradation of 2,5-dichloronitrobenzene were investigated.Anaerobic degradation of 2,5-dichloronitrobenzene by bacterial communities enriched with additional carbon sources (pyruvate, formate, acetate and lactate) was investigated. The results showed that pyruvate-amended bacterial community exhibited the best ability to reduce nitro group, which was completely biotransformed in 4 h; Meanwhile, acetate-amended community had the best dechlorination and degradation ability, and its degradation rate of 2,5-dichloroaniline were about 12% higher than that by pyruvate-amended community. In consideration of microbial growth, nitro-reduction and dechlorination rates, pyruvate was assumed to be the best additional carbon source. Degradation mechanism analysis showed that 2,5-dichloronitrobenzene could be anaerobically transformed to CO2 via 2,5-dichloroaniline,2-chloroaniline, aniline and hexanoic acid as intermediates by using HPLC, LC-MS and GC-MS. Microtox acute toxicity test indicated that EC50 values of 2,5-dichloronitrobenzene,2,5-dichloroaniline,2-chloroaniline and 3-chloroaniline were 99.36 ±3.97 mg L-1,84.32+2.72 mg L"1,142.76+5.14 mg L-1 and 107.18+4.36 mg L-1, respectively. The results showed that 2-chloroaniline had the lowest acute toxicity, which is of great significance for chloronitrobenzenes bioremediation under anaerobic conditions. PCR-DGGE revealed that genera Clostridium sp., Eubacterium sp., Streptomyces sp. and Propionibacterium sp. might play important roles in 2,5-dichloronitrobenzene biodegradation.Reductive dechlorination of chloroanilines is the rate-limiting step in the process of 2,5-DCNB degradation. Accordingly,2-aminoanthraquinone/graphene (AQ-GO) composite material was used as a novel mediator and its enhancement effect on chloroaniline biodegradation was investigated under anaerobic conditions. The results showed that the degradation rate of 2-chloroaniline in AQ-GO-supplemented system (k=9.38×10-2 d-1) is higher than those in control(k= 1.82×10-2 d-1), AQ (k= 2.32×10-2 d-1) and GO-supplemented systems (k=2.78×10-2d-1). Further analysis found that in AQ-GO-supplemented system extracellular polymeric substances increased 139.96 mg L-1, 113.41 mg L-1 and 77.08 mg L-1 compared with those in control, AQ and GO-supplemented systems, respectively. Dehydrogenase activity was 2.21-,1.54-and 1.32-fold higher than that in control, AQ and GO-supplemented systems. Similar results were also obtained in the degradation of the dechlorination product aniline in the presence of AQ-GO, AQ and GO, respectively. It can be concluded that AQ-GO composite material promoted the secretion of extracellular polymeric substances and increased the electron transfer activity of cells. Illumina MiSep high-throughput sequencing analysis revealed that AQ-GO composite material amendment resulted in the enrichment of electrochemical activity bacteria Ruminococcus, unclassifiedjClostridiaceae and unclassified_Prophyromonadaceae, Enterobacter, which could use additional or self-secreted redox mediators to accelerate the electron transfer for enhancing anaerobic biodegradation of 2-chloroaniline and aniline. |
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