The refinement of the N2O emission factor originating from treated sewage water in rivers with different water qualities

Treated sewage water flowing into rivers contains nitrogen (N) compounds, producing nitrous oxide (N₂O) through nitrification and denitrification reactions. In Japan, environmental reference values have been set for water quality for various locations within waterways, and these are classified into six different categories based on the level of water quality. This study aimed to refine the N₂O emission factor originating from treated sewage water by conducting year-round research on the production of dissolved N₂O in rivers with varying concentrations of organic matter, N, and dissolved oxygen. There were differences in the N₂O emission factor derived from the nitrification reaction of ammonium (NH₄)-N due to the impact of N pollution load caused by the inflow of treated sewage water into rivers with different water qualities. The calculated N₂O emission factor for rivers with relatively high water quality concentrations was 0.0028 kgN₂O-N kgNH₄-N^-1, and the calculated average N₂O emission factor originating from treated sewage water in rivers was 0.0026 kgN₂O-N kgNH₄-N^-1.