Microbial Community Structures In Mixed Bacterial Consortia And Their Application In Azo Dye Treatment Under Aerobic And Anaerobic Conditions

Azo dyes are one of the most versatile used syntheic dyestuffs because of their ease and cost effectiveness in synthesis and chemical stability. They have been widely used in textile, leather, printing and cosmetic industries. However, during the dyeing process, upto15%of the dyestuffs are discharged into the environment. These dyes are regarded as relatively persistent pollutants because they are extremely stable when exposed to light and aerobic conditions. Moreover, most of the biotransformation products of azo dyes are aromatic amines and they have been shown to be carcinogenic and mutagenic. Thus, industrial wastewater containing azo dyes must be treated before it is released into the environment. Many new processes have been developed for azo dye decolorization and the biodegradation of azo dyes has been considered as the most promising strategy.In this study, two consortia which could efficiently decolorize different azo dyes under anaerobic and aerobic conditions were enriched, respectively. PCR-DGGE analyses were performed to compare community dynamics and microbial stuctures between the two consortia, and the strains which were responsible for azo dye declorization in the two consortia were finally identified. Then, an anaerobic active sludge was built by using the two microbial population and the decolorization characteristics of the sludge were study. All of these might provide a possible way for azo dye treatment by using consortium. The main results are as follows:(1) In this study, two consortia which could decolorize methyl red (MR) under anaerobic and aerobic conditions were enriched, respectively. Thirteen pure strains from the two consortia were isolated and identified by16S rDNA sequencing. The results showed that all of the thirteen isolates were facultative anaerobic bacteria of the family Enterobacteriaceae. The research of the degradation characteristics of the microbial population indicated that the consortia had significantly higher azo dye decolorization rate compared to the individual strains, anaerobic consortium had a better decolorization rate than aerobic consortia. Both of the two consortia could decolorize different azo dyes effectively in a short time, and tolerate wasterwater with high azo dye concentrations.(2) PCR-DGGE analyses were performed in this study to analyze the microbial diversity of the two bacteria consortia. The results revealed that the microbial community changed significantly when MR was initially added into the media. Then, the microbial community reached a relatively stable stage when the consortia adapted to the dye-containing environment. Phylogenetic analysis indicated that microbial populations in the anaerobic compartment contained Klebsiella, Escherichia, Bacillus and Clostridium; the populations in aerobic compartment belong to Klebsiella, Buttiauxella and Bacillus.(3) In this study, the characteristics of the anaerobic sludge were investigated. The results indicated that Methyl Orange could be decolorized effectively by the sludge. The anaerobic sludge could tolerate and degrade Methyl Orange at high concentrations. The sludge could decolorize about98%Methyl Orange in144h even the dye concentration was reached to1000mg/L.The sludge could decolorize azo dyes with different structures and had the ability to decolorize repeated additions of dye aliquots.