Accurate Calculation Method for Urban Domestic Sewage Centralized Collection Rate Based on Water Quality and Quantity Variations

Abstract

Rapid urbanization has created significant challenges for domestic sewage management, particularly in accurately assessing sewage collection rate. A systematic analysis of globally adopted indicators for assessing sewage collection reveals a key limitation of existing calculation methods: they do not adequately account for variations in water quality and quantity within sewer networks, leading to biased results. To address this issue, this study proposes a new method for calculating the sewage collection rate. This method incorporates two key parameters-external water BOD₅ concentration and sewer BOD₅ degradation rate-to quantify external water infiltration, and to capture the effects of water quality and quantity variations on sewage collection rate. Applying this method, the domestic sewage centralized collection rates were calculated to range from 83.29% to 90.67% in Changzhou and from 76.40% to 81.88% in Shenzhen. Sensitivity analysis showed that the sewer BOD₅ degradation rate and the external water BOD₅ concentration affected the results by 0.25 and 0.042, respectively. Based on these findings, we propose several strategies to improve calculation accuracy, including developing a BOD₅ degradation rate model, deploying smart drainage systems, establishing cross-sector data-sharing platforms, and formulating standardized guidelines for calculating sewage collection rate. This study provides theoretical support for global sewage management.