Study On Pollution Control Of Overflow Of Combined Flow System Pipe Network Based On SWMM Model

Because some older urban areas have combined drainage systems,which can essentially meet local drainage needs on a sunny day but result in significant amounts of overflow sewage that cause water pollution and even the phenomenon known as"city looking at the sea,"the existing urban layout has failed to meet the requirements of environmental protection as urbanization has accelerated."City looking at the sea"phenomena.In order to study the overflow pollution control aspects of the combined flow system network,a drainage canal will be used as the study’s target.To control overflow pollution,three different strategies will be used:source control,process control,and end-of-pipe storage.The work builds a surface runoff model for a site in Guixi using rainfall data from Guixi.The overflow volume and the pipeline’s interception volume against overflow pollution are simulated for five scenarios with n₀=1 to 5 in order to choose the interception multiplier of the intercepting combined flow network.The five possible scenarios are then cost-analyzed,and the best interception multiplier is chosen using the ideal point approach and normalized calculations to strike a balance between the economy and the environment.The end of the storage is proposed to use the pool to control overflow pollution,using the pool equation to determine the effective volume of the pool,simulating the optimal depth of the pool under various reoccurrence periods,considering economic and environmental factors to select the best depth of storage,and finally analyzing the storage effectiveness of the pool.By evaluating the effects of four LID measures—bioretention ponds,green roofs,permeable pavements,and green roofs—Source Control proposes to LID the study area.This will allow it to choose the most effective retrofit solution based on the area’s current conditions and the interception effect.The entire project’s economic investment study is then completed.The study’s findings are as follows:（1）The interception effect of various interception multipliers on overflow pollution in the low rainfall season and high rainfall season was simulated based on the average precipitation of different months,When n₀=1 is used as the interception multiplier,19.82%to 24.19%of the overflow sewage can be intercepted.When n₀=3 is used,37.47%to 49.21%of the overflow sewage can be intercepted.When n₀=5is used,47.32%to 62.75 percent of the overflow sewage can be intercepted.The optimal point approach and normalisation calculations show that an economic-environmental balance can be reached when the retention factor is n₀=3.（2）The volume of the storagetank was initially calculated to be 2479m³in accordance with the Outdoor Drainage Design Code and combined with the volume of Guixi’s dry season wastewater.The storage depth of the storage tank was then examined under various return periods to determine the best storage depth of 6mm.Pollutant reduction rates for TSS,COD,TN,and TP were correspondingly 50.38%,45.36%,54.9%,and 58.3%.（3）After analyzing the effects of various LID changes,bioretention ponds and permeable pavements were chosen as the final LID facilities and installed on both sides of the road,covering 3.5%and 4%of the research area,respectively.The aforementioned three measures were combined to examine the impact of combined multi-measures on the control of overflow pollution.It was found that the overflow flow and overflow pollutants（TSS,COD,TN,and TP）were reduced at rates of 79.4%,80.2%,77.1%,82.3,and 79.2%,respectively,under the combined arrangement of multi-measures at the return period P=1,and that the reduction effect on overflow increased with the lengthening of As the duration between raindrops grows,the lowering effect of pollutants steadily decreases.The overall project’s ultimate cost analysis came to￥121.553 million.This serves as a guide for upcoming overflow pollution control.