Enhanced degradability of polycyclic aromatic hydrocarbons by combined chemical oxidation and biodegradation

A laboratory-scale study has been conducted to develop a bioremediation strategy by combining biodegradation and chemical oxidation. The combination was attempted to overcome the inherent bioavailability limitation of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) in a former manufactured gas plant (MGP) soil. Fenton's reagent (H2O2 + Fe2+) was very efficient in the destruction of PAHs from soil including naphthalene, fluorene, phenanthrene, pyrene, and benzo(a)pyrene. However, the optimum pH for the reaction was about 2. The low pH made the process incompatible with biological treatment and poses potential hazards to the soil ecosystem where the reagent is used. In order to overcome such limitations, a Fenton-type reaction was performed at near neutral pH by using ferric ions and chelating agents such as catechol and gallic acid. Calcium carbonate was used to maintain the pH of the system near neutrality throughout the reaction. By the combined treatment of the modified Fenton's reagent and biodegradation, more than 98% of 2- or 3-ring hydrocarbons and between 70 to 85% of 4- or 5-ring compounds were degraded in the MGP soil, maintaining its pH around 6.