Muneaki HAMAGUCHI Efficiency of ozone treatment of an excess sludge by a micro bubble Shuji HIMENO,Toshiya KOMATSU Since the excess sludge which occurred by the activated-sludge process widely adopted Japan includes organic matter of non-biodegradable, the efficiency of the methane fermentation is low if excess sludge is used methane fermentation as effective utilization of biomass. Therefore, it expected that the degradabillty of excess sludge is improved by ozone treatment and the efficiency of methanogenesis is enhanced. On the other hand, ozone generation is entail a lot of costs. Therefore, since micro bubble has size of less than 1 mm and efficiency dissolve gases in water, ozone treatment of excess sludge is improved by using micro bubble. The purpose of this study was evaluation of solubilization of excess sludge by micro bubble ozone treatment using staticmixer and confirmation of transition of amount of methane gas generation by using excess sludge after ozone treatment. At first, gas liquid ratio (G/L) was changed between 5 % to 20% at ozone concentration of 140 mg/L because the effects of G/L ratio on solubilization of excess sludge was evaluated. The low G/L ratio was few ozone in exhaust gas and able to efficiency dissolve ozone gases. However, there was no difference of amount of increase soluble COD (S-COD) between each G/L ratio, and it found that amount of increase S-COD was affected by consumption of ozone. The methane fermentation batch experiment(36}1 of mesophilic digestion) was made for 20 days using ozone treatment excess sludge after. Methane fermentation experiments were used untreated excess sludge and ozone treatment excess sludge that S-COD was about 900 mg/L. Amount of methane gas was increased about 10% if G/L ratios of ozone treatment were 5% and 10%. In contrast, Amount of methane gas was increased about 20% if G/L ratios of ozone treatment were 15% and 20%. It considered that ozone treatment of high G/L ratio caused efficient degradation organic matter which contributed to methanogenesis. Moreover, value of S-COD wasnft index of increase of amount of methane gas in methane fermentation, I considered that it is important to resolve to organic matter which contribute to methanogenesis. It was found that ozone treatment could be efficiency resolved of excess sludge in this study. Although the ozone treatment of high G/L ratio discharged a lot of exhaust ozone gases, it suggested that efficient ozone dissolution caused increase of biogas at methane fermentation.