A Review of the Biological Decolorization of Synthetic Azo Dye From Textile Wastewater by Bacterial Strains

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.