Screening, Identification, Decolorization Conditions And Mechanisms Of Bacterial Strains For The Degradation Of Azo Dyes

The common characteristics of textile effluent were its high intensity of color, stability of chemical structure and persistence. Such pollutant was regarded as one of the most difficult for remediation. Azo dye had the highest proportion and consisted70%of the total amount of dyes. The physical and chemical methods which deal with textile effluent have many disadvantages, such as high treatment cost, uncompleted and easy to cause secondary pollution. It is need to screen strains which could degrade azo dye efficiently and be used in dye wastewater treatment. In this study, with an integration of microbiology, molecular biology and biochemistry, the degradation conditions of strains and advantages and disadvantages of this method were studied with the provision of corresponding theoretical data and technical support for the application of biological treatment of dyeing wastewater. The main contents in this study include:1. A bacterial strain, ACT1, with ability to decolorize Reactive Black5(RB-5), was isolated from soil samples collected nearby textile factory. Phenotypic and phylogenetic analyses of the16S rDNA sequence indicated that ACT1belonged to Bacillus sp. Through UV random mutagenesis method, a mutant strain was obtained. Compared to Bacillus sp. ACT1, the decolorization rate of RB-5significantly increased. The strain was called Bacillus sp. YZU1.2. Bacillus sp. YZU1showed great capability to decolorize various reactive textile dyes, including azo dye. Static conditions with pH7.0and40℃were considered to be optimum for decolorizing RB-5. Bacillus sp. YZU1grew well in medium containing high concentration of dye (100mg/l), resulting in approximately95%decolorization in120h, and could tolerate up to500mg/l of RB-5. Bacillus sp. YZU1had the ability of tolerating salt and continuous decolorization. The decolorization rate of continuous seven batches had not significantly reduced. Bacillus sp. YZU1could adapt to a wider range of environmental conditions. 3. The study found that the decolorization of RB-5by Bacillus sp. YZU1was mainly depended on biodegradation through the enzyme produced by the strain rather than adsorption. The azoreductase activity in crude protein of Bacillus sp.YZU1was approximately7.50U/mg.When the concentration of RB-5was less than500mg/l, the decolorization kinetic equation of RB-5fitted he first-class kinetics model. The relationship between decolorization rate and dye concentration could be described by Haldane inhibition equation. The degradation rate of RB-5by Bacillus sp. YZU1increased when the the concentration of RB-5was less than300mg/l, but it decreased when the the concentration of RB-5was more than300mg/l.4. The decolorization of mainly used azo dye was higher than70%, indicated that the strain had the potential to treat complex dye wastewater.Based on the above results, the decolorization conditions by bacteria in laboratory-scale was achieved and further investigated could be applied to industrial dye wastewater treatment. The study exhibited an active role in further research by using biological methods to treat dye wastewater.