Effects of fill modes on N2O emission from the SBR treating domestic wastewater

Nitrous oxide (N2O) gas is emitted as an intermediate in the biological nit rogen removal process. A track study was performed to investigate the chara cteristics of N2O emission depending on the cyclic mode oia sequencing batc h reactor (SBR). A major emission of N2O took place at the aerobic phase, w hile N2O emission at the anoxic phase was insignificant. Especially, the hi ghest N2O emission rate was observed at the initial stage of aerobic phase under the limited dissolved oxygen (DO) condition. Under such a condition, nitrite (NO2-) was transiently accumulated along with significant N2O emiss ion due to incomplete nitrification. In addition, N2O production at the aer obic phase was strongly related with incomplete denitrification by nitrifie rs. N2O emission could be reduced by change in fill modes in the SBR. A sig nificant conversion to N2O took place in the SBR with the anoxic fill mode, while only small amount of N2O was conversed in the SBR with the aerobic f ill mode, Relatively high concentration of ammonia nitrogen (NH4+) accelera ted N2O production at the aerobic phase in the SBR with the anoxic fill com pared to the aerobic fill. For control of N2O emission in the SBR, the aero bic fill mode could be an effective method even if denitrification efficien cy may be reduced at the anoxic phase.