Contribution of dissolved N2O in total N2O emission from sewage treatment plant

Abstract The characteristics of nitrous oxide, N 2 O, from a sewage treatment plant, which conducts nitrogen removal, and the river that receives its effluent water, were investigated by intensive daily surveys in summer and winter. N 2 O production in the sewage treatment plant was promoted in winter when nitrite accumulated in the reaction tank. The dissolved N 2 O concentration in the effluent water was also high in winter, which caused the dissolved N 2 O concentration to increase in the river downstream. In contrast, the N 2 O production inside the plant and the dissolved N 2 O emission through the effluent water, the dissolved N 2 O discharge, was controlled in summer when the nitrogen removal was more complete and there was no-nitrite accumulation. The dissolved N 2 O in the effluent water was rapidly lost after leaving the plant by as much as 26% in summer and 59% in winter. Additionally, the amount of the dissolved N 2 O discharge in winter was almost equal to that of the indirect N 2 O emission. When the nitrogen removal proceeded successfully, the amount of dissolved N 2 O discharge was small. In contrast, when the nitrogen removal was insufficient, the dissolved N 2 O discharge became an important N 2 O source.