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The ozonation and the Fenton treatment of soil spiked with a mixture of eleven polycyclic aromatic hydrocarbons (PAH) were studied. The efficiency of the treatment was strongly dependent on the matrix of soil (sand or peat). PAH adsorbed on sand undergo degradation more easily and require less oxidants (ozone, hydrogen peroxide) than PAH adsorbed on peat. Soil ozonation and the Fenton treatment were effective not only for the removal of 3-ring PAH, but could effectively degrade also 4-, 5- and more ring PAH. PAH removal from soil with the Fenton treatment in slurry was found to be dependent on the ratio of H2O2/soil/Fe2+, the manner of addition of hydrogen peroxide, and the treatment time. Three-phase ozonation of PAH contaminated soil resulted in a lower PAH removal and required higher ozone doses than two-phase ozonation. An improvement of the biodegradability during the chemical oxidation favours the implementation of combined chemical treatment and biodegradation for remediation of PAH contaminated soil.

This study describes the removal of polycyclic aromatic hydrocarbons (PAHs) from creosote oil contaminated soil by modified Fenton's reaction in laboratory-scale column experiments and subsequent aerobic biodegradation of PAHs by indigenous bacteria during incubation of the soil. The effect of hydrogen peroxide addition for 4 and 10 days and saturation of soil with H(2)O(2) on was studied. In both experiments the H(2)O(2) dosage was 0.4 g H(2)O(2)/g soil. In completely H(2)O(2)-saturated soil the removal of PAHs (44% within 4 days) by modified Fenton reaction was uniform over the entire soil column. In non-uniformly saturated soil, PAH removal was higher in completely saturated soil (52% in 10 days) compared to partially saturated soil, with only 25% in 10 days. The effect of the modified Fenton's reaction on the microbial activity in the soil was assessed based on toxicity tests towards Vibrio fischeri, enumeration of viable and dead cells, microbial extracellular enzyme activity, and oxygen consumption and carbon dioxide production during soil incubation. During the laboratory-scale column experiments, the toxicity of column leachate towards Vibrio fischeri increased as a result of the modified Fenton's reaction. The activities of the microbial extracellular enzymes acetate- and acidic phosphomono-esterase were lower in the incubated modified Fenton's treated soil compared to extracellular enzyme activities in untreated soil. Abundance of viable cells was lower in incubated modified Fenton treated soil than in untreated soil. Incubation of soil in serum bottles at 20 degrees C resulted in consumption of oxygen and formation of carbon dioxide, indicating aerobic biodegradation of organic compounds. In untreated soil 20-30% of the PAHs were biodegraded during 2 months of incubation. Incubation of chemically treated soil slightly increased PAH-removal compared to PAH-removal in untreated soil.

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