Study On The Decolorizing Characteristics And The Catalysis Mechanism Of Redox Mediators During The Azo Dyes Biodegradation Processes

A great variety of synthetic dyes are used for textile dying and other industrial applications. Approximately,10 presents of different dyes used industrially was released into the environment before which was not treated. The characters of azo dyes, including toxicity, mutagenicity, teratogenicity, threaten the health of human seriously. Therefor, it is important to decolor the wastewater which contained all kinds of dyes. Nowadays, the biological method is the most effective and secure.This study is to explore the speed of degradation of azo dyes in anaerobic active sludge by anthraquinone. The decolorizing characteristics of azo dyes by anthraquinone were investigated and the effects of all kinds of factors on decoloration were studied. Analysis the change of strains structure, which was incubated in different carbon sources by anthraquinone mediators. In addition, the mechanism of azo dyes decolorization in anaerobic active sludge by anthraquinone and its step-limited were explored through the inhibitors and electric chain. The anthraquinone immobilized was used in the continuous degradation process to investigate the repetition rate of using. All the above can offer the favor for industrial application of related strains. The results of this study were following:(1) In this study, we took Methyl Orange as that was decolorizated, acclimated the dye-decolorizing anaerobic sludge to explore the acceleration effect on the dye-decolorizing by antheaquinone. The result found that the addition of menadione, lawsone, AQS and bromoamine acid could all accelerate the process of dye-decolorizing. The results demonstrated that the addition of quinoid redox mediators significantly increased the rate of decolorization of Methyl Orange. The research indicative the optimal anthraquinone was the menadione and its concentration was 0.1 mmol/L.(2) In present study, we put different electron donors into the system of anaerobic active sludge of decolorizating dyes to explore the effect on the speed of decoloring Methyl Orange by menadione. The result implied when formate was the sole carbon source, the effect on decolorization of Methyl Orange by menadione was the optimum. In addition, PCR-DGGE analysis was performed to reveal the strains’structure change of degradation Methyl Orange by menadione in an anaerobic active sludge which contained different carbon sources, respectively. Phylogenetic analysis indicated that microbial populations in the anaerobic compartment belong to Hydrogenophaga, Arthrobacter, Paenibacillus, Dechloromonas, Kocuria rosea, Fusibacter, Clostridium, Enterobacte and Citrobacter were present in the anaerobic compartment.(3) In the study, the effects of all kinds of factors on decoloration by menadione were studied, including the temperature, pH and salinity of the culture medium. The results indicated the anaerobic active sludge exhibited a good decolorization ability in ranges of pH from 7.0-9.0, temperature 30℃ and salinity from 0%-1%. During the degradation process, the removal rate of COD was 48.9%. During the continuous seven times repeat experiments, about 95.46% of Methyl Orange was degraded. In addition, in the study, the anaerobic active sludge could decolorizate the concentration of Methyl Orange 4.8 mmol/L. Besides, menadione can accelerate the speed of degradation of different azo dyes, such as Methyl Red, Ponceau S, Gongo Red and Eriochrome Red B, whose decolorization effecience had improved respectively from 1.5 to 21.8 fold. That indicated menadione could accelerate to decolorate varied azo dyes nonspecifically.(4) Under the metabolic transfer inhibitors, we studied the electron carrier participated in biological related process and its rate-limited step of quinine-mediated decolorization of Methyl Orange. In this study, inhibitor rotenone which implied on azo redutase rarely had not inhibited the decolorization of Methyl Orange, which could demonstrate decolorization of Methyl Orange did not reply on azo redutase under anaerobic condition. When NaN3, CuCl2 and dicumarol were regarded as inhibitors, respectively, the decolorizations all decreased, which indicated the decolorization process was replied on the electric transfer of respiratory chain on the cell membrane. Besides, the mechanism for quinine-mediated reduction of azo dyes consisted of two independent reaction steps:first, the quinones are reduced by quinone reductase to the corresponding hydroquinones; second, the hydroquinones reductively cleave azo bond in a purely chemical redox reaction. These results indicated that the reduction of menadione to the hydroquinone form by the anaerobic sludge was the rate-limiting step in the reduction of Methyl Orange.(5) In this study, anthraquinone immobilization beads by CA and PVA, respectively, without bacteria were examined for their decolorizating of azo dye. Repeated-batch operations were performed to examine the reusability of the anthraquinone immobilization beads for azo dye decolorization. Compared with one immobilized by PVA, the immobilized beads by CA had a higher mechanism, a better stability. After 4 runs, the immobilized menadione could keep high catalytic activity to decolorize repeated additions of dye aliquots.