The refinement of the NO 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 (NO) 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 NO emission factor originating from treated sewage water by conducting year-round research on the production of dissolved NO in rivers with varying concentrations of organic matter, N, and dissolved oxygen. There were differences in the NO emission factor derived from the nitrification reaction of ammonium (NH)-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 NO emission factor for rivers with relatively high water quality concentrations was 0.0028 kgNO-N kgNH-N, and the calculated average NO emission factor originating from treated sewage water in rivers was 0.0026 kgNO-N kgNH-N.