Chiraphorn Kornsitthikul creator Samorn Muttamara Chairperson Takizawa, Satoshi Examination committee Dahl-Madsen, Karl Iver Examination committee Government of the United Kingdom Scholarship donor text th Bangkok Asian Institute of Technology 1998 monographic eng 69 leaves Three treatment systems, namely ozonation, activated sludge and combination of preozonation and activated sludge were investigated for the removal of COD, BOD, Oil & Grease and TSS from petrol station wastewater. All experiments were run in batch mode. The application of ozone in petrol station wastewater was effective to oil removal. Three ozone dosages of 4. 63, 10.30 and 14.08 mg 0 3/L 0 2 were used in this study. The optimum conditions were accomplished at ozone dosage of 14.08 mg 0 3/L 0 2, contact time of 60 minutes and at neutral pH. The removal efficiencies of COD, BOD, TSS and Oil & Grease were be 60.713, 69.103, 53.443 and 65.593 respectively. The pH of wastewater showed great influence on the efficiency of ozonation. Ozonation can promote biodegradability and also destabilize the suspension of wastewater. However, in some cases, ozonation gave negative effect on biodegradability. Biological treatability of this wastewater was also carried out in this study. The activated sludge systems were operated with two organic loading levels (F/M ratio) of 0.25 and 0.38. The removal efficiencies of COD and Oil & Grease with F/M ratio of 0.25 were found to be higher than those of 0.38, but detention time of the former was twice higher than that of the later. Further investigations on effect of preozonation at different pH on perfo rmance of the sequential activated sludge treatment system were also made. The results indicated that the pH conditions of the preozonation step played a significant role in the subsequent biological treatment processes. BOD removal efficiency of preozonation at low pH was higher than that of individual treatment. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development Thesis (M.Sc.) - Asian Institute of Technology, 1998 Sewage Purification Ozonization Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B12748 http://203.159.5.9/ait-thesis/detail.php?q=B12748 011298 20260817162153.0