Enhanced degradation of polycyclic aromatic hydrocarbons by biodegradationcombined with a modified Fenton reaction

A study has been conducted to enhance degradation of a mixture of polycycli c aromatic hydrocarbons (PAHs) by combining biodegradation with hydrogen pe roxide oxidation in a former manufactured gas plant (MGP) soil. An active b acterial consortium enriched from the MGP surface soil (0-2 m) biodegraded more than 90% of PAHs including 2-, 3-, and 4-ring hydrocarbons in a model soil. The consortium was also able to transform about 50% of 4- and 5-ring hydrocarbons in the MGP soil. As a chemical oxidant, Fenton's reagent (H2O2 + Fe2+) was very efficient in the destruction of a mixture of PAHs (i.e., naphthalene (NAP), fluorene (FLU), phenanthrene (PHE), anthracene (ANT), py rene (PYR), chrysene (CHR), and benzo(a)pyrene (BaP)) in the model soil, no ticeably, 84.5% and 96.7% of initial PYR and BaP were degraded, respectivel y. In the MGP soil, the same treatment destroyed more than 80% of 2- and 3- ring hydrocarbons and 20-40% of 4- and 5-ring compounds. However, the low p H requirement (pH 2-3) for optimum Fenton reaction made the process incompa tible with biological treatment and posed potential hazards to the soil eco system where the reagent was used. In order to overcome such limitation, a modified Fenton-type reaction was performed at near neutral pH by using fer ric ions and chelating agents such as catechol and gallic acid. By the comb ined treatment of the modified Fenton reaction and biodegradation, more tha n 98% of 2- or 3-ring hydrocarbons and between 70% and 85% of 4- or 5-ring compounds were degraded in the MGP soil, while maintaining its pH about 6-6 .5. (C) 2001 Elsevier Science Ltd. All rights reserved.