Enhanced Biological Decolourzation Of Azo Dyes By The Quinoid Redox Mediators

Because of their chemical stability, ease of synthesis and versatility, azo dyes are widelyused in printing, paper-making, cosmetic and textile dyeing industries. Azo dyes withcomplex structures and high toxicity are usually difficult to degrade. In this paper, propertiesand treatment methods of azo-dye-containing wastewater was reviewed. Based on analysis ofdisadvantages of various methods, A/O method was believed to be the best one. Enhancementby redox mediator is an effective method to increase the performance of anaerobicdecolorization.An efficient quinone-reducing bacterial community was enriched to increase the rate ofquinone-mediated azo dye decolorization. The enrichment of the community and the growthof the community were reported. Enhancement of decolorization by quinone compounds wasstudied. The effects of several redox mediators were compared.Bacterial community was obtained from the sediments of fresh water river and anaerobicactivated sludge by addition of concentrated substrate. RISA(Ribosomal Irltergenic SequenceAnalysis) was used to analyze the change of the community. The increase of concentrationsof KE-3B and AQDS was helpful for the growth of community in logarithmic phase. It wasspeculated that the azoreduction was in fact anaerobic respiration. Bacterial communityobtained energy through this process, pH=5-8 was suitable for the growth of the community,while pH 5.8-6.4 and 7.0-7.4 was suitable for stable quinone reduction. Glucose concentrationwas in 0-2 g/L, The growth of the community was enhanced with the increase of glucoseconcentration. However, excess glucose led to growth competition between quinone-reducingbacteria and other ones, which inhibited the quinone-reducing activity.Enhanced biological decolorization of azo dyes by the catalysis of quinone redox mediatorswas investigated using quinone-reducing community. The results indicated that the bacterialcommunity can enhance decolorization of many azo dyes with AQDS as a redox mediator.For Reactive Brilliant Red KE-3B, the optimum decolorization conditions were as follows:pH 6～9; glucose, AQDS and KE-3B concentrations between 0.05％～0.1％, 10～100 mg/L andless than 600 mg/L, respectively. Under such conditions, 90％decolorization was reached in18 h. Moreover, the bacterial community could utilize several intermediates of anthraquinonedyes as redox mediator to accelerate the decolorization of Reactive Brilliant Red KE-3B.