Characteristics And Mechanisms Of Degradation Of Synthetic Dyes Using Anaerobic Sludge And NZVI

Dye wastewater is the main contamination in the world caused by modern industry, it should be treated harmlessly before discharge into environment since most kinds of the dye wastewater are poison to human. Anaerobic sludge has been proved to be an efficient and inexpensive method which also has a wide range of application used in wastewater and other environmental fields. In this study, an artificially acclimated anaerobic sludge was used to degrade wastewater including azo dyes, anthraquinone dyes as well as triphenylmethane dyes. Investigated the accelerate effects of synthetic SiO2 coated nZVI in anaerobic reactor.The result demonstrated that the acclimated sludge has an obvious advantage over one single strain in aspects of the degradation rate and scope. In this study, the final degradation rate of selected dyestuffs are satisfied. The average degradation rate of azo dyes is over 80% in 12 hours, most of the anthraquinone and triphenylmethane can also be degraded more than 70% in 12 hours. Dyes were continuously added into degradation system for 10 days, the result shows that the degradation rate in the last day is still acceptable, and there was no drastic fluctuation during these days. The measurements of COD in system show that there is a dramatic decrease in the first 6 hours, and then the degradation become slowly until the end of the reaction, and finally COD decrease to 52% of the initial value.The result of DGGE indicate that the microbial community has been changed with the increase of dyes concentration. The number of some bacterial strains in sludge increased, some decreased while others remain stable. Phylogenetic analysis indicated that microbial populations in the sludge belong to Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi and Proteobacteria.The degradation products of the three kinds of dye were identified. As for azo dyes, the anaerobic sludge could degrade Methyl Orange to N, N-dimethylbenzene-1,4-diamine and 4-aminobenzenesulfonic acid. For triphenylmethane dyes, after Malachite Green was decolorized, the analyzed products were found to be a mixture of N, N-dimethyl-benzenamine,3-dimethylamino-phenol and 4-dimethylaminobenzophenone. For anthraquinone dyes, two products (acetophenone and 2-methylbenzoic acid) could be indicated after Reactive Blue 19 decolorization.The TEM result of SiO2-coated nZVI demonstrated the average grain diameter ranges from 15 to 20 nm, the thickness of the outside SiO2 film is consistent and approximately lOnm. SiO2-nZVI is more resistant to oxidation than nZVI and the acidic environment will definitely increase the decolorizaition rate. The co-degradation experiments demonstrated that synthetic SiO2-coated nZVI can accelerate the degradation of dyes.In this study, the anaerobic sludge was acclimated successfully which possesses the ability of degrading azo dyes, anthraquinone dyes and triphenylmethane dyes. Investigate the microbial structure in sludge and the mechanisms during the degradation. Explore the accelerate effect of synthetic SiO2-coated nZVI in this process preliminarily.