Ecological impacts of combined sewer overflows on receiving waters

Abstract Receiving water quality is increasingly recognized as a significant environmental issue due to rapid urbanization and climate change. The quality of water in urban streams is notably affected by discharges from waste water treatment plants (WWTPs) and sewer systems, particularly during combined sewer overflows (CSOs). WWTPs are essential for processing wastewater from both point and non-point sources, which is critical for the sustainable development of water supply systems. Nonetheless, the efficiency and performance of these plants can be significantly impacted during heavy storm events. This paper provides a concise overview of the various factors that lead to CSOs, the primary consequences of these overflows on receiving waters, and the mitigation strategies currently implemented to alleviate their adverse effects. Additionally, it discusses best management practices and strategies that have been developed to enhance the resilience of WWTPs against storm events. The paper also highlights contemporary environmental threats, including micropollutants, microplastics, and bioaerosols, while identifying gaps and challenges in the existing literature regarding these pollutants. Finally, it outlines prospective research avenues and recommends effective management strategies to address the impacts of CSOs on receiving waters.