Optimizing initial chlorine dosage at an injection point along a water distribution pipe

Abstract

This study proposed a gradient-based optimization framework for determining the optimal initial chlorine dosage at an injection point along a water distribution pipe, with the aim of ensuring microbial safety and regulatory compliance while minimizing chlorine overuse and associated costs. Leveraging the SNOPT (Sparse Nonlinear Optimizer) algorithm integrated within the COMSOL Multiphysics environment, the approach systematically refined dosing strategies based on temperature-dependent chlorine decay dynamics. Prior to optimization, a uniform dosage of 1 mg/L yielded suboptimal outlet residuals; 0.30 mg/L, 0.23 mg/L, and 0.17 mg/L at 290K, 300K, and 310K, respectively. Post-optimization, precise dosing of 0.66 mg/L, 0.87 mg/L, and 1.16 mg/L achieved the target residual concentration of 0.2 mg/L across the same temperature conditions, enhancing disinfection control by 13-17%. The results demonstrate that this method delivers accurate, adaptive chlorine dosing, reducing the risk of harmful disinfection byproducts (DBPs), improving cost efficiency, and supporting sustainable water quality management. The proposed model is suitable for real-time integration into supervisory control systems, offering a practical pathway for advancing water safety, operational effectiveness, and environmental stewardship.