Optimization design of vertical subsurface flow constructed wetlands and water distribution engineering

A vertical subsurface flow constructed wetland for the enhanced treatment of wastewater treatment plant tailwater is adopted as the research object. A complex large-scale system mathematical model is established with the head loss of the water distribution network pipeline as the coupling constraint condition; the hydraulic retention time of the constructed wetland, the economic flow rate of the water distribution pipeline, and the optional standard pipe diameter of the pipeline as the feasible domain constraint conditions; the height of the constructed wetland pool and diameter of the water distribution branch and trunk as the decision variables; and the minimum total annual cost of vertical subsurface flow constructed wetlands and water distribution engineering as the objective function. This model is first optimized through orthogonal experiments. Under different experimental combinations, the large system decomposition–dynamic programming aggregation method is used to obtain the annual cost target value of the project. The range analysis method is then employed to obtain the optimal experimental combination. Thereafter, the large system decomposition–dynamic programming aggregation method is used to obtain the minimum annual cost target value of the project and the optimal values of the above decision variables. In this article, the vertical subsurface flow constructed wetland and water distribution engineering of a sewage treatment plant in Jiangsu is chosen as an example for comparative analysis of the conditions before and after optimization. The research results show that the optimization design method proposed in this article can reduce project construction and operation costs and generate economic benefits.