Biodegradation of soil-applied polycyclic aromatic hydrocarbons by sulfate-reducing bacterial consortium

In the present study, the potential of polycyclic aromatic hydrocarbons (PAHs) biodegradation by sulfate-reducing bacterial consortium enriched from piggery wastewater was investigated. The batch experiments of soil-applied PAH biodegradation were conducted with a mixture of PAHs, i.e., naphthalene, fluorene, phenanthrene, fluoranthene and pyrene, at a concentration of 50 mu g of each PAH per g of soil. A central composite design (CCD) was applied to determine the experimental conditions of each batch assay. The pH, biomass and ethanol concentrations were selected as independent variables and the PAH removal percentage was considered as a dependent variable. The optimal conditions for PAH biodegradation were found to be a pH between 4 and 6.5, an ethanol concentration less than 35 mg/L and a biomass concentration greater than 65 mg/L. Bench scale experiments were carried out at the optimal conditions. At the end of experiment (27 d), total PAH removals by biodegradation and volatilization were around 74% and 20%, respectively. The order of PAH removal was naphthalene, phenanthrene, fluorene, fluoranthene, and pyrene. Throughout the study, PAH biodegradation was in good correlation with sulfate reduction. Results of the kinetics study indicated a competitive inhibition between PAHs investigated.