STRATEGY FOR CONTROLLING NITROUS OXIDE EMISSION IN OXIDATION DITCH REACTOR BY OPTIMIZATION OF STIRRING METHODOLOGY: CONTINUOUS MONITORING AND LARGE-SCALE EXPERIMENT IN FULL-SCALE SEWAGE TREATMENT PLANT

The purpose of this study is to make stirring method for controlling nitrous oxide (N2O) production with successful nitrogen removal in an oxidation ditch reactor with rotator. Continuous measurements of N2O and water quality were performed under different stirring conditions. As the result, spatiotemporal distribution of dissolved oxygen (DO) and N2O concentration was different depending on the stirring pattern. In the stirring pattern that adequately makes anoxic zone and aerobic zone in the reactor, dissolved inorganic nitrogen removal ratio was accomplished as 74% and N2O emission factor was low as 0.31%, respectively. The N2O production was affected by the profiles of influent, DO, and organic carbon, which implies that existence of anoxic zone and supply of organic carbon promotes the N2O reduction. Based on the results, strategy for controlling the N2O emission in full-scale sewage treatment plant based on the stirring methodology was provided.