改进的水质服务水平与加氯费用优化分析

为了能够综合表征供水管网中余氯及消毒副产物三卤甲烷(THMs)对水质的影响,建立THMs中不同组分的服务水平表达式,采用平均值、标准差和连乘3种表达式建立关联余氯及THMs服务水平的水质服务水平表达式.为了优化管网二次加氯时的加氯费用,提出考虑加氯点建设费用和基于加氯质量浓度的次氯酸钠溶液消耗量的加氯费用表达式.采用Net3管网模拟余氯衰减和THMs生成,优化算法采用非支配排序遗传算法（NSGA-Ⅱ）,将计算得到的Pareto前沿面进行对比.计算结果表明,加权平均表达式为关联余氯和THMs服务水平的最优方式.随着二次加氯点数量的增加,水质服务水平的最大值增加,较高水质服务水平时的加氯费用降低.管壁余氯衰减系数对Pareto前沿面的影响最大,其次为加氯点数量、基于余氯消耗的THMs生成比例系数和出厂水THMs质量浓度,出厂水最小余氯质量浓度的影响可以忽略.

Optimal analysis of improved water quality performance and rechlorination cost

The expressions of service level about different composition of THMs were built in order to comprehensively describe the effect of residual chlorine and disinfection by-products trihalomethanes (THMs) on water quality in water distribution systems. The expression about water quality service level of residual chlorine and THMs service level was built with three expressions including average values, standard deviation and multiplication. In order to optimize the cost of rechlorination, an expression of chlorination cost was presented by considering construction cost of boosters and the sodium hypochlorite consumption based on initial chlorine concentration. Then an multi-objective model of water quality performance and rechlorination cost was presented. Net3 water distribution system was used to simulate chlorine decay and THMs formation. The non-dominated sorted genetic algorithm-Ⅱwas used to optimize the algorithm and Pareto fronts generated were compared. Results showed that the weighted average expression was the optimal way to correlate service level of chlorine and THMs. With the number of boosters increasing, the maximum value of service level of water quality was increased and the rechlorination cost under higher service level of water quality was decreased. Decay coefficients of chlorine wall had the most effect on Pareto frontier, then number of boosters, proportionality coefficient of THMs concentration in effluent and THMs formation based on chlorine consumption. The effect of minimum chlorine in effluent could be ignored．