Monitoring of petroleum hydrocarbon degradative potential of indigenous microorganisms in ozonated soil Yeonghee Ahn 1, *, Haeryong Jung 2 , Rameshwar Tatavarty 2 , Heechul Choi 2 , Ji-Won Yang 1 & In S. Kim 2 1 Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technol- ogy, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea; 2 Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju 500-712, Korea (*author for correspondence: e-mail: yahn@kaist.ac.kr) Accepted 26 May 2004 Key words: biodegradation, gene probe, ozonation, petroleum hydrocarbon, remediation, soil Abstract This study was performed to investigate the petroleum hydrocarbon (PH) degradative potential of indig- enous microorganisms in ozonated soil to better develop combined pre-ozonation/bioremediation tech- nology. Diesel-contaminated soils were ozonated for 0–900 min. PH and microbial concentrations in the soils decreased with increased ozonation time. The greatest reduction of total PH (TPH, 47.6%) and aromatics (11.3%) was observed in 900-min ozonated soil. The number of total viable heterotrophic bac- teria decreased by three orders of magnitude in the soil. Ozonated soils were incubated for 9 weeks for bioremediation. The number of microorganisms in the soils increased during the incubation period, as monitored by culture- and nonculture-based methods. The soils showed additional PH-removal during incubation, supporting the presence of PH-degraders in the soils. The highest removal (25.4%) of TPH was observed during the incubation of 180-min ozonated soil during the incubation while a negligible removal was shown in 900-min ozonated soil. This negligible removal could be explained by the existence of relatively few or undetected PH-degraders in 900-min ozonated soil. After a 9-week incubation of the ozonated soils, 180-min ozonated soil showed the lowest TPH concentration, suggesting that appropriate ozonation and indigenous microorganisms survived ozonation could enhance remediation of PH-con- taminated soil. Microbial community composition in 9-week incubated soils revealed a slight difference between 900-min ozonated and unozonated soils, as analyzed by whole cell hybridization. Taken together, this study provided insight into indigenous microbial potential to degrade PH in ozonated soils. Introduction Many studies have shown that ozonation is effec- tive in removing contaminants such as petroleum hydrocarbons (PH) from soil (Hus & Masten 1997; Lim et al. 2002; Nelson & Brown 1994; Stehr et al. 2001; Sung & Huang 2002). Molecular ozone or its decomposition products (e.g., hydroxyl radicals) react with organic compounds to convert them into oxidized products. Oxidized products resulted from ozonation can be more water-soluble and/or more bioavailable than parental compounds, which leads to better biodegradation (Gilbert et al. 1983, 1987; Legube et al. 1981). Although the strong oxidizing activity of ozonation can remove PH effectively, ozonation is an expensive process since ozone generation requires a high-voltage electric discharge to oxygen molecules. Studies on pre-ozonation and subsequent bio- degradation have been performed to enhance remediation of soils contaminated with PH com- ponents, such as polycyclic aromatic hydrocarbons Biodegradation (2005) 16: 45–56 Ó Springer 2005