Bacteria-assisted bioremediation of azo dye pollution: challenges, recent progress, and future directions

The widespread use of azo dyes in the textile, food, and leather industries results in the production of large volumes of wastewater, which is considered a major threat to ecosystems and human health. These dyes inhibit photosynthesis in water and may release carcinogenic aromatic amines. Traditional physicochemical methods are usually expensive and energy intensive and produce secondary xenobiotics; therefore, greener methods are needed. Bioremediation with the help of bacteria has become a potential, environmentally friendly, and yet economically viable tool for addressing azo dye pollution. In particular, this review examines the effectiveness of Bacillus spp. in the degradation and detoxification of different azo dyes in textile effluent. It describes the enzymatic processes, especially the involvement of azoreductases and other oxidoreductive enzymes, by which such bacteria break recalcitrant azo bonds under both aerobic and anaerobic conditions. New technological progress in maximizing these microbial processes, such as the effects of key physicochemical variables and the evolution of sophisticated bioreactor technologies to increase degradation and scalability, is discussed. Nevertheless, the buy-down process in the lab in the field is not without challenges, including the complexity of dye structures, the stability of the dye in mixed waste streams, and optimization of the process. These hurdles, which are discussed critically in this review, and future directions, such as genetic engineering of strong bacterial strains and complementing biological approaches with other technologies, are the way forward in ensuring the sustainable treatment of industrial wastewater.