Making waves: Rethinking our mission for N2O emissions at WRRFs

• Key limitations in estimating WRRF and water body N 2 O using emission factors. • Redefining the source of WRRF N 2 O emissions as the waste itself. • Proposing refined emission factors and holistic approaches to N 2 O mitigation from wastewater. Nitrous oxide (N 2 O) is a potent greenhouse gas with a global warming potential 273 times that of CO 2 , and it is a significant contributor to ozone depletion. Water resource recovery facilities (WRRFs) have been identified as a major source of N 2 O emissions, leading to significant research and policy efforts to mitigate these emissions. As WRRFs undertake these N 2 O mitigation efforts, important questions remain regarding the impact of more intensive nitrogen removal for pollution prevention and public health protection and how reactive nitrogen discharges are emitted as N 2 O in receiving waterways. To answer these questions, this perspective highlights the importance of balancing facility-scale emission factors to estimate N 2 O emissions from wastewater while considering the impacts of nitrogen if discharged to receiving water bodies. This perspective suggests more comprehensive approaches to manage N 2 O emissions, emphasizing the need to account for the reduction in N 2 O emissions achieved through nitrogen removal at WRRFs compared to direct discharge into receiving water bodies. By considering the overall impact of nitrogen from wastewater on N 2 O emissions from both WRRFs and receiving water bodies, WRRFs can reduce their impact on the environment while maintaining their important role in removing nitrogen from wastewater.