Estimation of Unintended Treated Wastewater Contributions toStreams in the Yangtze River Basin and the Potential Human Healthand Ecological Risk Analysis

"Clean water and sanitation"is one of the UnitedNations Sustainable Development Goals. One primary objective ofwastewater treatment is to remove contaminants such aspathogens, nutrient, and organic matter from wastewater, whilenot all contaminants could be removed effectively. Wastewatertreatment plants would inevitably represent concentrated pointsources of residual contaminant loadings into surface waters. Thisstudy focuses on the populated Yangtze River Basin whereemerging contaminants are frequently detected in the rivers in therecent years. A python-based ArcGIS model is developed toestimate the contributions of effluent discharges in water supplysources and quantify fate and environmental risks of human-derived contaminants in the river network. Wefind that one-third of theriver networks are potentially influenced by the effluents through local or upstream inputs. Average fraction of unintendedwastewater reuse in water supply intakes is estimated to be lower than 3% under the averageflow scenario with an average travelingtime of 0.05 day from the nearest effluent input site to water supply intakes. However, under lowflow scenario, the percentage ofeffluent discharge would increase largely, leading to substantial increases in human health and ecological risks. This study provides asystematic investigation to understand extents of impacts of effluent inputs in river networks as well as identify the opportunities toimprove the water management in the densely populated regions