Efficient biodegradation and detoxification of reactive black 5 using a newly constructed bacterial consortium

Abstract

The release of azo dyes into wastewater from textile industries poses a significant environmental challenge due to their toxicity and recalcitrance. Among these dyes, Reactive Black 5 (RB5) is one of the most widely used and environmentally persistent due to its complex aromatic structure, high stability, and extensive use in the textile sector. This study aimed to develop and optimize a highly efficient bacterial consortium for the decolorization and detoxification of RB5. Three bacterial species-Bacillus cereus, Proteus mirabilis, and Stenotrophomonas maltophilia-were isolated from industrial effluents and combined into a consortium based on compatibility testing. The optimization of cultural and incubation conditions using Plackett-Burman Design (PBD) and Central Composite Design (CCD) significantly enhanced RB5 decolorization efficiency, reaching 98.56% under static conditions. Enzymatic analysis revealed the crucial role of NADH-DCIP reductase and azoreductase in azo bond cleavage, while oxidative enzymes facilitated further degradation into non-toxic metabolites. Metabolite characterization using UV-Vis, FTIR, and GC-MS confirmed the breakdown of RB5 into intermediate compounds with reduced toxicity. Toxicity assessments demonstrated a 66.38-21.38% reduction in root growth inhibition, an increase in germination rate from 40 to 93.33%, a decrease in Artemia salina mortality from 86.7 to 23.3%, and a reduction in cytotoxicity from 55.31 to 14.45% in human breast epithelial cells. These findings demonstrate the potential of the developed consortium as an eco-friendly, cost-effective solution for RB5-contaminated wastewater. Future studies should focus on pilot-scale implementation, long-term stability under variable effluent conditions, and regulatory compliance for industrial deployment.