Influencing factors and control suggestions for overflow pollution in areas with combined sewer system

Overflow pollution during flood season in areas with combined sewer system has become an important reason for the return of urban rivers to blackness and odor, and the effective control of overflow pollution plays an important role in improving the water environment quality and enhancing people's sense of well-being, accessibility and security. In view of the prevention and control of overflow pollution in flood season in areas with combined sewer system, the characteristics of overflow wastewater, the influence on water environment quality, and the influencing factors of overflow pollution were summarized. The distribution characteristics of areas with severe overflow pollution were analyzed and the control suggestions were put forward. The study found that the overflow wastewater from combined sewer systems in China had the characteristics of complex composition, large changes in water quantity and quality, and poor quality of initial rainwater, which caused urban non-point source pollution and led to the deterioration of surface water. By analyzing the countrywide distribution of two main influencing factors of overflow pollution, i.e. precipitation and pipe network conditions, it was preliminarily identified that the areas with serious overflow pollution were mainly distributed in the south and east of China. The correlation analysis showed that there was a moderate correlation between precipitation in flood season, pipe network density and regional water quality. In order to strengthen the prevention and control of overflow pollution in areas with combined sewer system, some specific suggestions were proposed, including developing discharge control standards for overflow pollution according to local conditions, updating technologies for controlling and treating overflow wastewater, enhancing the whole process management of overflow pollution in flood seasons, and strengthening effectiveness assessment of overflow pollution control and treatment, and so on, which hopefully could provide support for effective control of overflow pollution and promote water environmental quality continuously.