Process Optimization and Kinetic Evaluation of Toluene Biodegradation Using Response Surface Methodology

Toluene is a major pollutant detected in opium processing industries causing various environmental hazards significantly harming aquatic as well as terrestrial organisms. Toluene toxicity directly affects the central nervous system, liver, kidney, reproductive organs, hearing and vision loss. Effective degradation strategy for removal of toluene from the biosphere is crucial. Accordingly, this work aimed to isolate potent microbial strains for the degradation of toluene. For this, soil samples were collected from a yard of Opium and Alkaloid factory. A mineral salt medium, supplemented with 100 ppm of toluene was used to isolate the bacterial cultures from these soil samples. Biochemical tests and 16S rRNA sequencing showed the selected strain as Bacillus haikouensis . Batch degradation study was conducted with 50–400 ppm of toluene and the optimal process parameters were evacuated for the temperature (32–40°C), pH (4.0–9.0) and inoculum size (2–8 ml per 100 ml). Central Composite Design with Response Surface Methodology (CCD-RSM) mathematical model was used to predict degradation which was eventually validated experimentally. HPLC was used to validate toluene degradation whereas GC-MS was carried out for treated samples to identify degraded products. Under various experimental conditions, toluene degradation achieved was between 77–82% at 100 ppm initial concentration of toluene. A maximum degradation of 83% was achieved in conjunction to the predicted degradation of 89% by CCD RSM. HPLC chromatogram confirmed degradation of toluene to different lighter metabolites. GC-MS showed the presence of derivatives of benzene and benzoic acid, toluene (residual), and benzaldehyde.