Multicycle Ozonation+Bioremediation for Soils Containing Residual Petroleum

The removal of total petroleum hydrocarbons (TPH) and other organic carbon using sequential biodegradation and ozonation in two soils (BM3 and BM4) was studied. The conditions for each step: 5% moisture content for ozonation and 10% moisture and circumneutral pH for biodegradation, were optimized. For the relatively biodegradable TPH in BM3, preozonation and postozonation strategies were equally effective. Meanwhile, the more recalcitrant TPH in BM4 was better treated using postozonation. Carbon analyses along the treatment timeline demonstrated that dissolved organic carbon (DOC) was the dominant substrate for microbial consumption when readily biodegradable TPH was no longer available. The carbon in TPH was more reactive with O₃ than was the rest of dichloromethane-extractable organic carbon (DeOC), and the fate of TPH dictated the changes of DeOC. However, the fate of total organic carbon was controlled primarily by the microbial mineralization of DOC. Ozonation did not directly enhanced the biodegradation rate of the residual TPH after ozonation, but ozone converted TPH into DOC that was microbially mineralized.