Anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aged deep soil pretreated with chemical oxidation

Integrated chemical-biological treatment of polycyclic aromatic hydrocarbons (PAHs) contaminated soil has received much attention. However, previous studies mainly focused on the remediation of soils contaminated with PAHs using oxidation treatment coupled with aerobic biodegradation, rather than anoxic biodegradation. In order to study the feasibility of applying combined chemical oxidation and anoxic biodegradation method to remediate PAHs contaminated soil, the anoxic culture of the soil oxidized by hydrogen peroxide was carried out. It was found that the removal efficiencies of 16 PAHs ranged from 33.3% to 95.9% after hydrogen peroxide oxidation, but the application of hydrogen peroxide resulted in a significant decrease of the number of bacteria in the soil, and the gene copy number of total bacteria in soil decreased by 3.5 orders of magnitude. However, bacterial numbers could be significantly recovered after 180 days of anoxic incubation in the treatment added with nutrients, and higher levels of bacteria were observed in treatments with nutrients and electron acceptor (sulfate) in inoculated soil. The use of nutrients or electron receptor (sulfate) alone could not enhance the biodegradation of PAHs obviously, but the application of both nutrients and electron acceptor could result in obviously biodegradation of PAHs. Moreover, higher biodegradation efficiency was observed for 3-rings and partial 4-rings PAHs (fluoranthene and pyrene) in inoculated soil than that of non-inoculated soil in treatment where both nutrients and electron acceptor were added. Overall, a further PAHs removal of about 15% was observed after anoxic biological treatment compared with chemical oxidation treatment alone.