Taku EGUCHI Oxidation and Emission of Dissolved Methane in the System Combined with UASB and DHS Reactors for Sewage Treatment Akiyosi OHASHI, Hideki HARADA UASB effluent inevitably contains dissolved methane, of which the fate generally goes to the air as greenhouse effective gas. In the system with aerobic post treatment process such as DHS, however, it is expected that the dissolved methane is biodegraded in the post process. In this study we investigated how much methane DHS reactor can biologically oxidize to CO2 while methane is physically emitted into the air. On the basis of the methane-oxidization activity, we estimated that the biodegraded methane was only ca. 8 % of the total amount of methane introduced into the DHS. The other methane of 92 % was to be physically released to the air. The methane concentration profile simulated by our developed mathematical model with the mass transfer coefficient and the methane-oxidization activity was significantly coincident with the measured one, supporting that most of the dissolved methane was physically emitted. In other words the function of methane oxidation was unluckily poor. In contrast, the fast gas transfer between the sponge and the air in the DHS reactor rapidly makes the dissolved oxygen in the sponge high, resulting in the excellent performance of aerobic organic removal without an external aeration input.