Study On Biodegradation And Decolorization Of Azo Dyes By Streptomyces FX645

Azo dye is one kind of toxic compound which contains azo bond and aromatic ring structure related to mutagenesis, carcinogenesis or teratogenesis, and it is difficult to be degraded. Using microbes from the activated sludge to degradate azo dyes is an important approach to treat wastewater containing azo dye.In this thesis, azo dye was treated by microbe fermentation through studying physiological and biochemical assay, Response-Surface Method (RSM) optimizing and the Liqiud Chromatogram Spetrum-Mass Spectum (LC-MS) analysis of degradation products, the strain identification, optimization of degradation condition, degradation pathway and degradation kinetics. And the results were as follows.(1) Five strains with decoloring capability for azo red30(AR30) were isolated from the activated sludge from dyeing workshop of one printing and dyeing factory, and were named as X1-X5, in which the strain X2has the best efficiency of decolorization with the hightest decolorization rate95%.(2) On the basis of the physiological and biochemical characteristics of the strain, the strain X2was primarily identified as Streptomyces. The bacterial16S rDNA gene sequence analysis of X2strain showed that it is mostly close to the Streptomyces variabilis with99%of identity. Therefore it was named as Streptomyces FX645.(3) The effect of aerobic/anaerobic, carbon nutrition, nitrogen nutrition, pH value, dye concentration, cultural temperature, cultural time on decolorization were studied, and it was found that the decolorization process was occurred on anaerobic condition. Glucose is the best carbon nutrition while ammonium chloride is the best nitrogen nutrition. The Streptomyces FX645can keep the higher activity of decolorization and degradation under anaerobic circumstance under pH5-9, dye concentration25-200mg/L and cultural temperature26-40℃. The decoloring conditions were optimized by the RSM, and the decolorization rate could reach95.8%under the conditions of dye concentration109.92mg/L, cultural time36.24h, initial pH value7.34and cultural temperature31.38℃.(4) The UV-visible spectra and LC-MS chromatogram were used to elucidate the degradation products of AR30. The UV-visible showed that the specific absorbance peak at445nm and at289nm almost disappeared, which indicated that azo bond of AR30was broken after degradation. The MS data showed that the degradation products as follows:2,6-dichloro-4-nitrobenzenamine,2,6-dichlorobenzene-1,4-diamine,2-((4-aminophenyl)(2-cyanoethyl)amino)ethylacetate,2-((4-acetamidophenyl)(2-cyanoethyl)amino)ethylacetate,3-((4-acetamidophenyl)(2-acetoxyethyl)amino)propanoic acid. Compared with the structure of the initial azo dye AR30, the decolorization mechanism of AR30could be mainly regarded that the azo-bond was reducted to aromatic amine as intermediate products by azoreductase in anaerobic conditions. According to the MS spectra of biodegradation products, the proposed degradation pathway of AR30of was obtained.(5) Decolorization of AR30conformed to first order kinetics when initial concentration of dye ranged from25to100mg/L under anaerobic condition. In the case of other conditions remain unchanged, the degradation rate is reduced with the increase of initial concentration of azo dyes. Through the kinetic model, hydraulic retention time in biological wastewater treatment can be estimated according to the initial dye concentration.Through the investigations on the decolorization and degradation of azo dyes using sludge bacterial fouded in printing and dyeing wastewater, the optimal degradation conditions, the degradation pathway and mechanism, first order kinetics were obtained which can provide basic data and the theoretical foundation for the in-depth research on the azo dye wastewater treatment procedure.