Modeling of Residual Chlorine on Addis Ababa Water Supply Distribution Systems

Abstract

Most developing countries especially sub-Saharan countries like Ethiopia struggle with poor drinking water quality problems. Hence, this research was conducted to model residual chlorine in the Arada sub-city supply system by using Water CAD ${V}_{8}$ program. The primarily collected data were existing chlorine concentration, bacteriological water quality, pH, and turbidity from thirty-two sample points. Sample points were taken from the water source, treatment plant, storage facilities, distribution network, and points of use. To identify the main problem and optimize the distribution system, the residual chlorine model was developed at the initial concentration under three different scenarios. Scenarios I: residual chlorine at the low hour and peak hour demand, scenario II: effects of old pipe, and scenario III: pressure on the oversized and undersized pipes. Hence, optimizing those scenarios were done by establishing additional chlorine injection point. The study result shows that the residual chlorine concentration was less than the minimum recommended WHO standards of 0.2 mg/L in a remote area and above the maximum recommended value 0.5 mg/L near the treatment plant. Bacteriological analysis showed that 31.4% of the sample point’s level of TC and FC were higher than the maximum permissible limit when compared to the values set by WHO due to the high chlorine demand of the wall decay rate and bulk decay rate. Therefore, there is a critical need to improve the efficiency of chlorination in the distribution system. The above scenario was improved residual chlorine efficiency but more best at low hour consumption scenarios.