As for optimizing performance of chlorine and trihalomethane (THM) in water distribution systems

an expression measuring THM performance and a derivation of THM-I/O model were proposed. And a multi-objective optimization model considering maximizing level of chlorine performance

maximum level of THM performance and minimizing cost of chlorination was also established. Four factors

including bulk chlorine decay coefficient

coefficient of proportionality between THM and chlorine consumption

initial THM concentration in treated water and number of boosters

were evaluated to study their effects on Pareto front of the multi-objective optimization model. Chlorine decay and THM generation were simulated using EPANET_MSX. An improved non-dominated sorted genetic algorithm-Ⅱwith integer code was proposed to optimize the model

and Pareto fronts could be obtained under different conditions. Results show that with the decrease of bulk chlorine decay coefficient

cost of chlorination can be reduced and level of THM performance will be improved. Diminishing coefficient of proportionality between THM and chlorine consumption and initial THM concentration out of reservoir can both improve the level of THM performance

but can not affect the cost of chlorination. Increasing number of boosters can reduce dosage of chlorine

but booster station construction will increase total cost of chlorination. There-fore

reducing the bulk chlorine decay coefficient is the most economical and effective method.