Nitrogen flows with its yearly change and magnitude in urban waste in Tokyo: Implications for nitrogen management

Urban areas are nitrogen (N) hotspots due to rapid urbanization compared to rural areas. Tokyo, as a typical urbanized city, represents an ideal model for analyzing N flows and the emissions of reactive N compounds (Nrs). As the first analysis of N flows in urban waste in Japan, this study calculated N inflow, stock, and outflow of Tokyo's 20 urban wastes (2000–2018), providing insights into their magnitudes and yearly changes. Results show that the total N inflow decreased from 66.26 to 64.71 Gg N yr−1 indicating a decline of 2.3 %. The average annual Nrs emissions including NH3, N2O, and NOx were calculated as 15.28 Gg N yr −1 (2015–2018). Sewage sludge N represented 57 % of the total N inflow, and its incineration contributed significantly to Nrs emissions. Our findings have significant implications for the sustainable management of N in urban waste in Tokyo and other Asian cities.