Azo dyes represent the largest and most extensively used class of synthetic dyes in industries such as textiles, leather, paper, food, cosmetics, and pharmaceuticals. Due to their complex aromatic structures and the presence of azo (–N=N–) bonds, these dyes exhibit high chemical stability and resistance to degradation, leading to their persistent discharge into the environment through industrial wastewater. This review provides a comprehensive overview of the chemistry, sources, environmental fate, and toxicological impacts of azo dyes, with a particular focus on microbial remediation strategies. The roles of bacteria, fungi, algae, and microbial consortia, along with their enzymatic mechanisms and influencing factors, are critically discussed. The presence of azo dyes in aquatic and terrestrial ecosystems causes severe environmental problems, including reduced light penetration, disruption of photosynthetic activity, and deterioration of water quality. Moreover, the reductive cleavage of azo dyes can result in the formation of toxic, mutagenic, and carcinogenic aromatic amines, posing significant risks to ecological and human health. Conventional physicochemical treatment methods, although effective in decolorization, suffer from limitations such as high cost, energy demand, sludge generation, and incomplete mineralization. This review identifies key strategies for achieving scalable and eco-friendly solutions for industrial wastewater management.
Gayathri et al. (Thu,) studied this question.