Optimization of Bioremediation of Phenol, 4-Chlorophenol, and Catechol by a Microbial Consortium Using Response Surface Methodology

Aerobic treatment of pharmaceutical wastewater was carried out using a microbial consortium comprising Brevibacillus formosus, Pseudomonas otitidis, Bacillus timonensis, Bacillus cereus, Bacillus pseudomycoides, and Bacillus paramycoides, isolated from contaminated soil to degrade a phenolic mixture of phenol, 4-chlorophenol, and catechol. Six operational parameters—initial phenolic concentration, pH, temperature, culture volume, inoculum size, and residence time—were optimized using a central composite design (CCD)-based response surface methodology (RSM) with 86 experimental runs. The second-order polynomial regression model validated by ANOVA confirmed significant individual and interactive effects (F-value: 30.59). Optimal degradation occurred at 1,500-mg/L initial phenolic load (500 mg/L each), pH 8.0, 600 mL culture volume, 45°C, 15% inoculum, and 48-h residence time, achieving 99.87% overall degradation. High-performance liquid chromatography (HPLC) confirmed 98.96% removal of phenol, 96.81% of 4-chlorophenol, and 98.60% of catechol. These results demonstrate the high efficiency and applicability of the developed consortium and model for phenolic wastewater treatment. To the best of the authors’ knowledge, this study represents one of the few reports demonstrating simultaneous aerobic degradation of phenol, 4-chlorophenol, and catechol at high total loading (1,500 mg/L) using a bacterial consortium optimized through a six-factor CCD–RSM approach.