Application of EPANET for the determination of chlorine dose and prediction of THMs in a water distribution system

INTRODUCTION The purpose of this study is to predict the level of chlorine residual and trihalomethanes (THMs) in a drinking water distribution system and to help operators to determine chlorine dose in a drinking water treatment plant (WTP) using EPANET 2.0. Water quality modelling was conducted by chlorine bulk decay and THM formation from bottle tests. Chlorine decay tests for the finished water of the WTP were performed on a monthly basis for one year. As the result, a simple equation for the target chlorine concentration in the finished water was derived by a multiple regression method in relation to initial chlorine concentrations, temperatures, total organic carbon and chlorine decay coefficients. The chlorine concentration after it leaves a WTP, before entering its distribution networks, is critical in maintaining chlorine residual levels throughout the system. It is apparent that the chlorine concen-1 tration of the finished water be maintained to be flexible to keep it at over 0.1 mg L throughout the system because chlorine consumption is different according to the season, flow and pipe networks. These chlorine values of the finished water are the target chlorine concentrations for determining the chlorine dosage to the filtered water in a WTP. As the results of this study using a multiple regression model for chlorine decay and EPANET, the target chlorine concentrations of the finished water were -1 -1 -1 set to 0.5 mg L in spring and fall, 0.55 mg L in summer and 0.45 mg L in winter. These values are slightly lower than the existing target values. .