Hamadan University of Medical Sciences Avicenna Journal of Environmental Health Engineering 2423-4583 12 2 2025 12 30 A Review of the Biological Decolorization of Synthetic Azo Dye From Textile Wastewater by Bacterial Strains 128 145 10.34172/ajehe.5491 EN Zahra Emadi https://orcid.org/0000-0002-8448-7842 Mehraban Sadeghi https://orcid.org/0000-0002-0751-1255 Solieman Forouzandeh REVIEW 10.34172/ajehe.5491 2024 04 25 2025 08 06 Artificial dyes are regarded as one of the most problematic environmental pollutants. They are widely applied in the textile, print, paper, paint, pharmaceutical, food, cosmetics, and leather industries. The textile industry produces large volumes of colored wastewater, along with other pollutants such as salts, toxic substances (e.g., heavy metals, biocides, and oxidizing agents), high organic load, nutrients, and sulfur. These dyes adversely affect living organisms and ecosystems by inhibiting photosynthesis and causing health disorders such as skin irritations, allergies, cancer, vomiting, and weakened immune reactions. Thus, they should be removed using physical, chemical, and biological methods. Chemical and physical methods need regeneration processes and chemical agents, and they are expensive. In contrast, bio-decolorization by bacteria, fungi, algae, and plants is an environmentally friendly and cost-effective technique. Bacterial strains can adsorb, degrade, and flocculate dyes. Biodecolorization is positively or negatively affected by operational parameters such as agitation, pH, temperature, dye concentration, carbon and nitrogen sources, salinity, electron donors, and redox mediators. As stated, these parameters have positive (optimum concentration) and negative (beyond optimum) impacts on decolorization efficiency.