Optimizing the locations of sewage treatment plants has enormous practical significance. In this study, a large-system mathematical model was developed for optimizing the locations of sewage treatment plants within a system and designing the associated pumping station pipe network. Head loss of pipe segments in the pipe network was the coupling constraint, the economic flow rate of pipe segments was determined by the feasible region constraints of decision variables, and the design variables were the sewage treatment plant locations, the design head of the pumping stations, the pipeline economic life, and the pipe diameter of divided pipe segments. The minimum total annual cost of the sewage treatment plant(s) and the pumping station pipe network was the objective function. A large-system quadratic orthogonal test-based selection method was used with a discrete enumeration comparison and selection method to determine pipeline economic life. A dynamic programming method was used to determine the pipe diameter of the divided pipe segments. By comparing the total annual cost of the sewage treatment plants and the associated pumping station pipe network corresponding to different pipeline economic lifetimes, the optimal solution that generates the minimum total annual cost can be identified. The sewage treatment plant and pumping station pipe network in Taizhou, China, was used as an example to compare and analyze optimization results. The new optimization method would have produced much lower annual cost than that of the existing system. This study provides valuable theoretical references for probing the layout design of urban sewage treatment plants corresponding to different pipeline economic lifetimes.
Keywords: Annual cost; Enumeration method; Optimization; Orthogonal test; Pipe network; Sewage treatment plant.