Cultivation of a Functional Microbial Consortium Using Biosolids and Its Effectiveness for Remediation of Soil Contaminated with Diesel Oil Y.C. Song, T.T. Nguyen, S.H. Kim*, G.J. Kim* and H.S. Park**, S.J. Ko***, C.Y. Lee**** Division of Civil and Environmental Engineering, Korea Maritime University, Busan 606-791, Korea (Email: soyc@hhu.ac.kr) *SGR Tech. Co., Ltd., No.701, Education Industrial Center, University of Ulsan, Ulsan 680-749, Korea (E-mail: supray@hanmail.net) **Dept. of Civil and Environmental Engineering, University of Ulsan, Ulsan 680-749, Korea (E-mail: parkhs@ulsan.ac.kr) ***Korea Institute of Maritime and Fisheries Technology, Busan 606-803, Korea (E-mail: kosung001@hanmail.net) ****Department of Civil Engineering, Suwon University, Kyeonggi–do 445-743, Korea (E-mail: chaeyoung@suwon.ac.kr) Abstract: Cultivation of a functional microbial consortium degrading oil using biosolids and its effectiveness for remediation of soil contaminated with diesel oil were studied. The mixtures of dewatered biosolids with three types of thickened biological sludge were put into aerobic fermentation vessels with sawdust and diesel oil. After the start up of the fermentation, the diesel oil added into the biosolids was rapidly degraded during first several days, and the percentages of the degradation were reached to 80 - 87% within 1 week. However, the degradation rates of diesel oil were decreased according to the decreases of diesel oil level contained in the mixtures of biosolids. After start-up of the fermentation, lots of carbon dioxide was produced, indicating the high activity of diesel oil degradation, and then the production was gradually reduced. The contents of diesel oil in the mixtures of the fermentation product with soil were rapidly decreased to 75-80% within 1week, and were amount to around 55ppm after 4 weeks. The degradation rate of diesel oil in the soil was dependent on the amount of the fermentation product mixed into the soil. Keywords: Biosolids; Bioremediation; Functional Microbial Consortium; Oil-contaminated soil. INTRODUCTION In Korea, the biosolids produced from wastewater treatment plant has been dumped into several special sea areas apart from the coastline. However, the ocean dumping for the disposal of biosolids could not be used any more if London convention comes into effect in the near future. Therefore, the biosolids problem concerning its treatment and disposal is a major issue for environmental engineers, now. Traditional methods for the biosolids disposal including landfill, incineration and pyrolysis could be also considered, but these methods also have lots of adverse effects on environment due to the spread of some hazardous pollutants contained in the biosolids (Ting et al., 1999). On the other hand, soil contaminated with oil is also another serious concern to be solved for the environmental engineer. Usually, bioremediation is one of the cost-effective methods for the cleaning of the soil contaminated with oil (Wang and Bartha, 1994). However, lots of bacteria which can degrade pollutants originated from oil and some nutritive substances are required for the bioremediation of soil contaminated with oil. Then, the biosolids from a biological treatment of wastewater is an aggregate of myriad bacteria containing lots of nutritive substances needed in microbial growth, as well as organic matter. The organic matter and the nutritive substances could be easily utilized for the growth of other bacteria during fermentation under substrate limited condition. This indicates that the biosolids has a great potential converting into the materials (inoculum and nutritive materials) for the bioremediation. In the study, it was investigated to determine if the biosolids could be used as a solid medium for cultivation of a microbial consortium utilizing diesel oil as a carbon source, and the effectiveness of the fermentation product for the remediation of soil contaminated with diesel oil was also estimated. 1123