Technical report: predicting chlorine residuals in water distribution system case study in Penang / Ilya Syakirah Mohamad Sidik, Nik Nuraziemah Ahmad Husni and Syahmin Adiba Abdullah

Chlorination is the most widely practiced form of disinfection in Malaysia. Chlorine plays an important role in maintaining the water quality in distribution system through a residual. In order to determine the optimal chlorine residual, it is necessary to predict the chlorine decay in water distribution network. Firstly, chlorine decay in bulk water need to be described clearly to understand the decay characteristics. The combination of first and second order model of ordinary differential equation was found to be one of the most suitable models for this purpose (Hua et al., 1999). In this report, an analytical solution for this model was developed where the second order decay equation is used for the initial phase to find decay constant k1 while for the second phase the first order decay equation is used to find decay constant k2 (Kowalska et al., 2006). This is because the first 4 hours of the initial phase has immediate consumption and after the first 4 hours the chlorine consumption is slower. From the data obtained, this project use Microsoft Excel and Harmonic Mean Method to find the decay constant k1 and decay constant kz. This project also used Sum of Square Error (SSE) to observe the error between the first order model and the combination of first and second order model. Based on the graph of chlorine residual (mg/L), it shows that the time taken for predictive chlorine residual to reach its minimum level is faster than that the actual chlorine residual. However, the results obtained from the proposed analytical solution was considered accurate in predicting of chlorine decay behavior.