Treatment of gaseous toluene in an anoxic hybrid bioreactor: Optimization using response surface methodology

This study focuses on treating gaseous toluene emissions from chemical and petrochemical industries using an anoxic hybrid bioreactor (AnHBR) and optimizing the process using response surface methodology (RSM). By varying the gas flow rate (0.05–0.25 LPM) of toluene, the gas residence time (GRT) within the AnHBR ranged from 0.53 to 2.67 h, resulting in an inlet loading rate (ILR) between 0.36 to 14.33 g/m³ h. Simultaneously, the hydraulic retention time (HRT) of the liquid feed was varied from 24 to 72 h in the AnHBR. The operating parameters were varied to determine the optimal combination to achieve the maximum toluene removal, which remained above 96% throughout the operation. At the optimized combinations (flow rate: 0.15 LPM, GRT: 0.89 h, and HRT: 48 h) in AnHBR, toluene removal reached ∼99%, with end products generated consisting of 1.8% CO₂ and 92.9% N₂ gas. Metagenomics analysis revealed a dominance of toluene degraders (∼38%), highlighting their potential to degrade toluene in the AnHBR. The RSM enhanced toluene treatment in the AnHBR, demonstrating robustness in handling high pollutant loads and its potential for industrial applications.