Residual chlorine modelling in drinking water distribution system of Bishoftu Town, Ethiopia
Kenatu Angassa, Mulatu Feyisa, Israel Tessema, Mikiyas Abewaa
Abstract
• Bishoftu town relies on groundwater, with declining quality causing waterborne diseases. • WaterCAD was used to model chlorine residual concentrations and water age in the system. • Residual chlorine concentrations ranged from 0.51 to 0.82 mg/L to 0.07–0.45 mg/L. • Water age exceeded recommended ranges, affecting chlorine levels and water quality. • Modeling residual chlorine and water age is key to improving Bishoftu's water system. The deterioration of treated water quality in distribution systems is influenced by factors such as disinfectant levels, water age, and the presence of microbial contaminants. This study presents a novel approach to analyzing and predicting residual chlorine concentrations and water age in the Bishoftu town water supply network, Ethiopia, using WaterCAD software. While previous studies have focused on chlorine decay, this research uniquely combines laboratory measurements with simulation results for a comprehensive understanding of chlorine dynamics. The laboratory results indicated that the mean residual chlorine concentrations at all junctions ranged from 0.51 to 0.82 mg/L during the first week, exceeding the WHO-suggested maximum of 0.50 mg/L. In subsequent weeks, concentrations decreased to 0.10–0.45 mg/L in the second week and 0.07–0.38 mg/L in the third week. The WaterCAD model effectively simulated chlorine dynamics and water age, with no significant discrepancies between lab measurements and simulation results ( p > 0.05 for all weeks). Notably, the model revealed that water age in the system exceeded the WHO recommended range of 48–72 h in several areas, contributing to accelerated chlorine decay. This study provides key insights into optimizing water distribution system design and operation. Specifically, it recommends the implementation of real-time chlorine monitoring, optimizing injection points to reduce chlorine loss, and redesigning the pipeline system to minimize water age and maintain optimal chlorine concentration. These recommendations are crucial to improve water quality and ensure public health protection in rapidly growing urban areas like Bishoftu.