Bacterial decolorization and degradation of azo dyes: A review

A variety of synthetic dyestuffs released by the textile industry pose a threat to environmental safety. Azo dyes account for the majority of all dyestuffs, produced because they are extensively used in the textile, paper, food, leather, cosmetics and pharmaceutical industries. Existing effluent treatment procedures are unable to remove recalcitrant azo dyes completely from effluents because of their color fastness, stability and resistance to degradation. Bacterial decolorization and degradation of azo dyes under certain environmental conditions has gained momentum as a method of treatment, as these are inexpensive, eco-friendly and can be applied to wide range of such dyes. This review mainly focuses on the different mechanisms of decolorization and discusses the effect of various physicochemical parameters on the dye removal efficiency of different bacteria. The enzymatic mechanisms involved in the bacterial degradation of azo dyes, the identification of metabolites by using various analytical techniques, and the nature of their toxicity has been investigated. This review provides an overview of bacterial decolorization/degradation of azo dyes and emphasizes the application of these processes for the treatment of azo dye-containing wastewaters.