Impact of nitrogen compound variability of sewage treated water on N2O production in riverbeds

Nitrous oxide (N2O), a strong greenhouse and ozone depleting gas, is known to be generated in the river environment. However, the impact of sewage treated water on the production mechanism has not been clarified. In this study, N2O production in the upper reach of a river was evaluated by field survey and activity test. The results demonstrated that the N2O production activity of the river pebbles increased with the inflow of the sewage treated water, which was supported by field survey results, such as the dissolved N2O concentrations and water quality. The emission factors of N2O were determined to be 0.02–0.05% in nitrification and 0.01–0.025% in denitrification. Our study shows that combining a field survey and an activity test improves the reliability of the results and leads to the appropriate quantitative evaluation. From a perspective of controlling the N2O emissions from the sewage treatment plant, N2O generation inside the plant is critical. However, appropriate nitrogen removal in the treatment plant is connected to the reduction of N2O generation in the river environment.