Assessment and modelling of residual chlorine in water supply systems: The case of Dangila Town, Ethiopia

Abstract

Application of chlorine for drinking water security in the water supply distribution network for the Dangila town is not well managed. The study was conducted by the help of Water CAD software to evaluate the chlorine dosing and residual chlorine model. The necessary data were taken from primary and secondary sources. Three scenarios were developed for modelling the residual chlorine content in the distribution system. Two scenarios were produced with chlorine dose of 0.6 mg/l at a flow rate of 26 ml/s and chlorine dose of 0.5 mg /l at a flow rate of 22 ml/s, respectively. Residual chlorine concentration above normal limits (0.5 mg/l) was recorded in both scenarios around the injection point whereas four sample points were below 0.2 mg/l. Scenario II, all residual chlorine values were lower than 0.5 mg/l but still lower than 0.2 mg/l at the farthest four sampling points.  In order to solve the above problem, A third scenario was developed with three reservoir injection points, Junction 4 and 55'' within 0.45, 0.15 and 0.2 mg/l of chlorine in order to maintain appropriate residual chlorine concentration.  Hence, the best solution identified from the analysis was the installation of two additional chlorine injection points.