A Study On Optimizing Rechlorination In Water Distribution Systems

At present, chlorine is the most widely employed disinfectant in drinking water treatment. A minimum free chlorine residual level of 0.05mg/L at the most end of the distribution systems is ordered to control the growth of pathogenic microbes as a safe drinking water standard in our country. Reactions of chlorine with organic matter can produce chlorination by-products (CBPs), which may be carcinogenic, teratogenic, or mutagenic. Other disinfectants may be used as an alternative to control the CBPs' concentration, and optimizing chlorination process also works. The study tries to control the CBPs' yield through optimizing the chlorine adding positions and dosages in the distribution system.At the first part of the paper, kinetics of chlorine decay in the water distribution systems are formulated and a first-order model is established on the basis of these. An approach named judging-mode is put out to calculate nodes' concentrations. The approach is translated and edited into Visual Basic langrage and works out the concentrations.Second part is the main content of the paper. Firstly, the optimization goal is put out, which tries to make the chlorine residual concentrations of nodes as low and equable as possible in the whole distribution system, on the premise that microbial security can be assured, through optimizing the chlorine adding positions and dosages in the system. Secondly, the model according to it and being based on the improved Genetic Algorithms (GA) is established.Finally, the performance of the decay model and optimization model presented above is demonstrated by application them into a two sources distribution network. The results show that the concentrations in the network are continuously dropping and becoming uniform. The optimization model works well and applying GA in it is a great success.