Exploiting microbial biomass in treating azo dyes contaminated wastewater: Mechanism of degradation and factors affecting microbial efficiency

Water pollution, mainly occurring from manufacturing industries, has been a serious environmental issue in the contemporary world. Dyeing processes produce a massive amount of dye-contaminated effluent; it is a major culprit for water and soil pollution in developing and underdeveloped countries. The azo dye released from industries poses a severe environmental menace by contaminating the aquatic system and adversely impacting human health. Azo dyes are synthetic macromolecules, which are persistent, recalcitrant, and non-biodegradable. Several physicochemical technologies have been proposed for azo dye mitigation. Still, some limitations are observed, such as high operational cost and energy requirement, complicated procedures, incomplete mineralization, and secondary waste generation. Alternately, remediation by microbes is considered a clean, effective, and safe technology to detoxify azo dyes from wastewater. The biological treatment can exploit fungi, yeast, bacteria, and algae, which have received attentiveness because of their eco-friendliness. This review highlights the decolorization and degradation of dyes by various microbes, acting as biological tools against azo dyes. It also discusses the azo dye degradation mechanism and factors affecting the degradations.