Analysis And Research Of Optimal Intercept Relationship Between Drainage System Of Confluence System

With the development of urbanization,the improvement of combined sewer system and the comprehensive control of the urban black and odorous inland river is a hot topic of research.Pollutant source control is fundamental to improving the environment,and interception ratio is an important parameter in the design of water environmental governance and the rehabilitation of combined sewer system,its value directly affects the overflow pollution of combined sewer system,pollution load,water environmental capacity and project investment.Therefore,it is necessary to synthetically consider the impacts of social,environmental and economic for the determination of interception ratio by means of optimization method.However,the determination and study of interception ratio mainly rely on subjective judgment,which is arbitrary and one-sided.As a result,what matters for the research is quantitative analysis of different interception ratio under the condition of drainage overflow results of the system and economic benefit.Finding the balance between the economy and the environment is the key to determine the optimal interception ratio.Storm Water Management Model?SWMM?was applied on a combined sewer system of the old city center in An long county,using the actual rainfall and monitoring data for the calibration and verification of the model.Simulating the process of intercepting pipe overflow within different return periods,rainfall types and interception ratio,and then compared the simulation results under the condition of different interception ratio with its economic and environmental benefits.By establishing the model of water environmental capacity,the simulation results of SWMM in the study area are combined with the water environmental capacity of the receiving water.Respectively determine the constraint conditions of economic and environment,and then,coupling the two objective functions.At the same time,Establish the optimal cut-off multiple model.Finally,The optimal cut-off ratio is determined by the maximum value of the environmental benefit of the unit investment.The results show that the SWMM model has a certain applicability and feasibility,in which the simulation study of the change process of the overflow hydraulic and water quality of the combined sewer system.In hydraulic simulation,In hydraulic simulation,the Nash-Sutcliffe coefficients E_ns of two rainfall events were 0.83 and 0.85,respectively;Meanwhile,in the water quality simulation,Nash-Sutcliffe coefficient E_ns of the outlet water quality indexes of TSS,COD,TN and TP were 0.84,0.82,0.83,0.86,respectively;Based on the results of n₀=1,along with the increase of interception ratio n₀,the reduction rates of the annual overflow were 15.25%,25.66%,31.79%,34.93%.The interception control rate of COD were 35.15%,38.66%,42.07%,45.10%,47.94%,respectively,while the interception control rate of TN were 38.35%,42%,45.87%,48.48%,51.45%,respectively.At the same time,the interception control rate of TP were 45.15%,50.12%,54.94%,59.27%,63.30%,The check standard of optimization of truncated multiple model functions by the constraint conditions of economic and environment,Taking the maximum environmental benefit of unit investment as the optimization objective,the optimal value of the interception ratio is finally determined to be 4.