Comparative Analysis for the Emission Amounts of Methane and Nitrous Oxide, and the Emission Characteristics with Operational Conditions of an Activated Sludge Process.

The emission amounts of CH4 and N2O discharged through each treatment process at a municipal wastewater treatment plant using an activated sludge process as well as their emission characteristics have been examined, taking into consideration such factors as whether the wastewater treatment plant uses nitrification acceleration as well as differences in water temperature between warm and cold seasons. The emission of CH4 was noticeable from both the aeration tank and the sludge thickener. The former is attributable to the fact that the density of CH4 in the wastewater influent increased as the compound passed through the primary sedimentation tank, which tends to be anaerobic, then flowed into the aeration tank and was driven out of it by the aeration action. The latter is attributable to the fact that the high-density organic compound had been stored for a long time. Also, it was revealed that the emission of CH4 is strongly influenced by the water temperature. The emission of N2O from the aeration tank was remarkable and strongly influenced by whether nitrification was occurred or not, and exponentially increased with the amount of NO3 generated during aeration process, which was attributable to variations of both microscopic pH and DO inside the activated sludge. The emission amounts of CH4 and N2O were estimated to be 6,7×109g and 2.5×108g per year in 1995, respectively, based on this study.