Assessing the contribution of wet-weather discharges on micropollutants release by urban catchments

Wet-weather discharges from integrated urban wastewater systems (IUWS) represent a threat for surface waters. When the system capacity is reached during medium/large rain events, a mixture of stormwater and untreated wastewater is discharged to surface water through Combined Sewer Overflows (CSOs) or Bypass (BP) of Wastewater Treatment Plants (WWTP). The loads of contaminants discharged by CSOs and BP are highly variable in time and space (Petrie, 2021), making it difficult to correctly monitor and assess the environmental risk for a specific catchment. The present work aims at assessing the impact of 12 micropollutants present in wet-weather discharges on receiving surface water, by using an archetype IUWS, defined through a stochastic approach. Monitoring data from literature were retrieved and elaborated to characterize the discharges and to predict the risk posed by micropollutants on a yearly horizon. The calculated risk from wet- weather discharges was compared against that posed by WWTP effluent (EFF).