Composite desirability-based multi-objective optimization of textile-dye biodegradation by novel Brevundimonas sp....

Improper discharge of untreated textile effluents comprising synthetic azo-dyes which are characterised by azo bond (-N = N-), poses severe environmental and public health concern due to persistence, toxicity and resistance towards conventional treatment techniques. This has created pressing need for low-cost, eco-friendly alternatives where microbial degradation shows effective remediation compared to chemical and physicochemical treatment methods, which are often costly, energy-intensive, and generate secondary pollutants. In this study, novel azoreductase-producing bacterium, Brevundimonas sp. AJZ05, was isolated from textile effluent and exhibited initial Direct Blue-6 decolorization efficiency of 85.24% and azoreductase activity of 0.172 U/mL. Plackett Burman design identified dye concentration, yeast extract, inoculum level as key variables influencing decolorization efficiency, while glucose, yeast extract, and inoculum level significantly affected azoreductase activity. Multi-response optimization via Response Surface Methodology with desirability functional approach determined optimal conditions: dye concentration (101.76 mg/L), glucose (5.19 g/L), yeast extract (5.87 g/L), and inoculum level (5.45%), achieving maximum decolorization efficiency (98.50%) and azoreductase activity (0.761 U/mL), corresponding to 1.1-fold and 2.83-fold increases, respectively. The optimized process remained effective in the presence of metal ions (Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺, Fe²⁺ at 0.5-1 mM), indicating its robustness under effluent condition. UV-Vis spectroscopy, FTIR, GC-MS and phytotoxicity analysis using Vigna radiata confirmed complete breakdown of DB-6 into less/non-toxic intermediates. Overall, Brevundimonas sp. AJZ05 exhibits strong potential for azo-dye bioremediation and toxicity reduction, showing significant promise towards environmental sustainability.