| Chloronitrobenzenes are known to be very toxic, resistant to microbial degradation and carcinogenic representative persistent organic pollutants which have been listed as priority pollutants by EPA and European Economic Community. In rescent years, Zero-valent iron(ZVI) has been used to degrade a range of organic pollutants, such as nitroaromatic compounds(NACs), RDX, azo dyes and so on. ZVI is a strong reducing agent that can reductivety transform electron-withdrawing nitro groups to amido groups, but it can't completely mineralize the organic pollutants, so it is necessary to coupled with biological or chemical oxidation processes.An integrated ZVI-SBR aerobic biodegradation system was conducted for the treatment of 2-chloro-nitro-benzene(2-CNB). Results of experiment showed this coupling process may be a feasible approach to enhance the degradability of chloronitrobenzenes-laden wastewater. To investigate the changes of sludge microbial community structure in SBR2 and SBR1 which treated 2-CNB and its ZVI reduced product(2- chloroaniline, 2-CA) respectively, the PCR-DGGE technology was used to analysis the dynamic of microbial community and microbial population diversity during the aerobic degradation processes of 2-CNB and 2-CA.DGGE analysis of PCR-amplified V3 region of the 16S rDNA gene fragments indicated that activated-sludge microbial community structures differed obviously during the degradation process of 2-CA and 2-CNB in SBR1, SBR2 respectively. Most bands of inoculation sludge disappeared and several specific bands appeared in the operation of two reactors. On the other hand, the bacterial community structure in the SBR1 was different from that in the SBR2. This was most probably related to the development of the dominant bacteria adaptation to the presence of 2-CA, 2-CNB.The similarities of PCR-DGGE band patterns among bacterial communities in SBRs taken on days 0, 8, 20, 32, 41, 52 and 60 were quantified using Dice coefficient(Cs). It indicated that the bacterial community structures exhibited a moderate shift at different phases. The Cs of bacterial communities in SBR1 and SBR2 showed 22 to 88.2, 31.7 to 83.9 respectively. Both two reactors had highly similar population fingerprints between day 8 and day 20(Cs=88.2, 77 respectively), because it was slow for microb in the response to 2-CA or 2-CNB. The results also showed that similarities of bacterial community structures in SBR systems were hightened with the increase of operation time, it indicated that bacterial community structures became stable.Compared with DOGE fingerprints, both two reactors had high bacterial population diversity. The DGGE fingerprints of two SBRs were analyzed using Shannon diversity index(S) and Equitability index(EI). The sludge samples from two SBRs did not show significant differences in their diversity and species distribution (SBR1:S=2.36-2.94, EI=0.92-0.98; SBR2:S=2.45-2.95, EI=0.9-0.969). This high bacterial diversity can positively maintain the stability of wastewater treatment system.In order to further understand the composition of sludge microbial population, special bands were purified and sequenced. Results demonstrated that the sludge microbial population structure of SBR1 was obviously different from SBR2's. It was found thatβ-Proteobacteria,ε-Proteobacteria, Sphingobacteriales, Flavobacteriales were shown to be the dominant groups in the process of SBR2 reactor, and the most dominant bacterias were closely related to Flexibacter sp., Flavobacterium sp., Pseudomonas sp.. Compared to SBR2 reactor, sludge samples from SBR1 had more abundant microbial population structure, includingβ-Proteobacteria,γ-Proteobacteria,ε-Proteobacteria, Flavobacteriales, Sphingobacteriates, Planctomycetales, Acidobacteria groups, and the most dominant bacterias were closely related to Pseudomonas sp., Flavobacterium sp., Acidobacteria bacterium. This multi-group bacterias in sludge is important to improve performance of the whole biodegradation system.
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