Evaluation and Modeling of Residual Chlorine in Dangila Town Water Supply System

Abstract

Application of chlorine for protection of drinking water in distribution system is not well established for the Dangila town. The study was conducted to assess chlorine dosing and model for residual chlorine using Water CAD software. The necessary dates were collected using primary and secondary sources. The existing maximum residual chlorine concentration at sample point 6 through the samples by 1.5 kg/m 3 chlorine dose with 3 ml/s flow rates was found to be 0.17 mg/l. Even, it was less than the minimum recommended WHO and ESA standard (0.2mg/l). The amount of total Coliform was found 5 colonies per 100ml and pH (8.68-9.1) and the remaining main chemical water quality parameters that analyses were found within WHO & ESA limits. In order to model the residual chlorine content 3 scenarios were developed. Scenario I and II were developed with 0.6 mg/l chlorine dose with 26 ml/s flow rate and 0.5 mg/l chlorine dose with 22 ml/s flow rate, respectively. In both scenarios residual chlorine concentration was recorded above the maximum limits (0.5mg/l) around the injection point which is a bit higher than the maximum limit, while 4 sample points got less than 0.2mg/l. Scenario II, all residual chlorine results were below 0.5 mg/l, but still the farthest 4 sample points got lower than 0.2mg/l. To solve the above problem Scenario III was developed with three injection points at reservoir, Junction 4 & 55`` within 0.45, 0.15 and 0.2 mg/l chlorine dose to keep the residual chlorine concentration acceptable. Therefore, installing two additional chlorine injection points were the best solution that identified from the analysis.