Abstract
Artificial dyes are regarded as one of the most problematic pollutants in the environment. They are applied in the textile, print, paper, paint, pharmaceutical, food, cosmetics, and leather industries. The textile industry produces high volumes of colored wastewater containing azoic, reactive, acid, basic, mordant, direct dyes, etc. In addition, other pollutants like salts, toxic substances (heavy metals, biocides, and oxidizing agents), high organic load, nutrients, and sulfur are present in the textile industry. Dyes harm living organisms and the environment by inhibiting photosynthesis, causing health disorders like skin irritations, allergies, cancer, vomiting, and reducing immunological reactions. Thus, they should be removed by physical, chemical, and biological methods. Chemical and physical approaches need regeneration and chemical agents, and are expensive. Bio-decolorization by bacteria, fungi, algae, and plants is an environmentally friendly and economical technique. Bacterial strains adsorb, degrade, and flocculate dyes. Biodecolorization is positively or negatively affected by operational parameters like agitation, pH, temperature, initial dye concentration, carbon and nitrogen sources, salinity, dye structure, electron donors, and redox mediators. As stated, parameters have positive (optimum concentration) and negative impacts (beyond optimum) on decolorization efficiency. Due to the characteristics of textile wastewater, different potent bacterial strains with special abilities (decolorizer, metal removal, and salt, alkaline, and thermo-tolerant strains) have been isolated, identified, and applied for treatment during recent decades. It should be noted that co-culture application instead of mono-culture increases the decolorization efficiency and reduces treatment time.