Removal of PAHs from Creosote Oil Contaminated Soil by Addition of Concentrated H2O2 and Biodegradation

This study describes the combined chemical, i.e. modified Fenton's reaction, and aerobic biological removal of polycyclic aromatic hydrocarbons (PAHs) in creosote oil contaminated soil. The initial concentration of eight selected PAHs (acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene and chrysene) was 4 g/kg soil. The soil was rich in iron (16.4 g Fe/kg soil) and slightly acidic (pH 5-6). Therefore, no pH adjustment or iron addition was performed. Aged contaminated soil was treated with 30% H2O2 in laboratory-scale, packed soil columns. The chemical treatment removed up to 52% of the total PAHs in the soil. The effect of the chemical treatment on indigenous PAH-degrading bacteria was studied by incubating untreated and H2O2 treated soil. Biodegradation of untreated soil removed up to 36% of the total PAHs. The indigenous PAH-degrading bacteria were able to survive aggressive chemical soil treatment with concentrated H2O2 and the combined chemical-biological treatment decreased the PAH-concentration by 55%. Introduction Creosote oil has been used extensively in the wood-preserving industry. Accidental spillage, improper disposal and misuse of creosote oil resulted in contaminated areas, with e.g. high concentrations of polycyclic aromatic hydrocarbons (PAHs) (7) of several grams per kg soil (2). In the Fenton's reaction hydroxyl radicals (HO*) are formed by the catalytical decomposition of hydrogen peroxide with ferrous iron acting as a catalyst (3): Fe + H2O2 — Fe 3+ + HO' + OH (1) Hydroxyl radicals are strong, non-specific oxidants that react with most organic compounds (4). The original Fenton's reaction was carried out at laboratory scale by slowly adding dilute H2O2 to an acidic Fe solution. This kind of procedure is impractical for many applications, such as contaminated soil remediation, thus modifications have been made to the process. Ferric iron containing compounds have been used as the reaction catalyst to minimize the consumption of H2O2 by the oxidation of Fe 2+ to Fe in the presence of H2O2 (5). Further, minerals of iron and other transition metals have been shown