Isolation of mixed bacterial culture from Rajshahi silk industrial zone and their efficiency in azo dye decolorization

Background: Textile wastewater has become one of the major sources of severe environmental pollution due to the increasing demand for textile products around the world. It contains toxic azo dyes which adversely affect the environment including water bodies, soil and all living organisms. Dye decolorization through microbial community is an area of extensive research; in addition to, removal of azo dyes from contaminated sites using microorganisms is an environmental-friendly and cost-competitive alternative to chemical decomposition processes. Hence, this study aimed to isolate some local bacterial strains, which possessed the ability to decolorize azo dye containing wastewater. Methods: The strains were isolated as mixed bacterial culture from textile effluent collected from Rajshahi silk industrial zone, Bangladesh. Different experiments were set up including-isolation of mixed bacterial culture, growth characteristics observation and optimization, finally treatment of dye containing wastewater. Results: The optimum growth of this culture was observed in LB medium containing 10g/L peptone and 5 g/L yeast extract, and the temperature ranges from 30 to 40°C, pH 7.2 to 7.5 and in the presence of light. Five different (0.5%, 1%, 5%, 10%, 15%) concentrations of dye containing wastewater (ash and green color) was treated in the temperature of 37°C in anaerobic condition and in the incubation period of 0 to 15days. The mixed consortia were more effective on low concentration of dye. Conclusion: The obtained results showed that the selected mixed culture had the ability to cleave azo bonds and thus they are capable to neutralize the textile azo dyes. It indicated that this mixed bacterial culture was able to utilize the dyes as their carbon and energy source. Extracellular enzyme of these bacteria which called azoreductase was responsible to cleave the azo bonds of used textile dyes.