Research On Overflow Simulation And Optimization Of Combined Sewer System

With the development of our society and promote the process of city?Most of the ground in the city is covered by residential,commercial and road areas,which greatly improves the water quality of the urban ground,resulting in the runoff coefficient increases,rainfall infiltration decreases,the surface runoff increases,in the case of heavy rainfall,it is easy to produce road water problems.As one of the drainage systems,the combined sewer system still exists in many old urban areas.Because of the aging of pipelines,it is prone to overflow and cause pollution to the surrounding water during the rainstorm?This paper uses SWMM model to model the old town of Chaohu City,research the rainfall intensity,surface impervious area ratio and the number of days before rain on the overflow of combined sewer system.And then puts forward the corresponding measures to control the pollution of the overflow from the source.Establish models in the study area.According to the land use situation in the study area,drainage direction,divided the area into 23 sub catchment area,23 nodes,25 pipe and3 discharge ports.Design rainfall by using rainfall hydrograph method in Chicago.According to the local rainstorm intensity formula,design rainfall peak coefficient r is 0.4,the rainfall recurrence period were 0.5 years,1 years,2 years,3 years,5 years,10 years of rainfall curve.The analysis of the influence of simulated rainfall intensity on overflow can be seen,the greater the intensity of rainfall,the more nodes in the overflow well,and the more water overflows.In the case of 0.5 year rainfall,there is no overflow,1 years,2 years,3years,5 years,10 years under the conditions,there are 2,3,5,6,8 nodes overflow.The maximum duration of overflow is 15 min.The content of pollution factors in overflow sewage is also affected to some extent.Under the different rainfall return period,the accumulation of TSS,COD,TN and TP showed a slow growth with time,increased rapidly in 40 minutes or so,and gradually reached a steady trend after 70 minutes.When the rainfall intensity meets 1 years from 0.5,there is a big difference in the total amount of pollutant accumulation,and then the change from 1 years to 10 years is not particularly obvious.Impervious surface also affects the quality and quantity of overflow water.The greater the area of impervious surface,the higher the total pollutant content in overflow water of unit area.In the case of different impervious surface area,the concentration of TSS and COD changes with the time at first,then decreases,and reaches the peak concentration inabout 50 minutes.The concentration of TN and TP are all reached the maximum value at the initial moment of the rainfall,with the passage of time,the rainfall,rainfall concentration decreases gradually.In the end,the concentration reaches a minimum value.The water quality and water quantity of the overflow before and after the 1 days,7days and 30 days of rainfall were simulated respectively to analyze the influence of the sunny days before rainfall on the overflow.From the results,we can see that the influence of the two rainfall interval days on overflow water flow is not particularly obvious,and has some influence on the overflow water quality.The accumulation of pollutants in sewage overflow and rain sunny days is proportional to.When the number of sunny days was 30 days,the content of TSS,COD,TN and TN in overflow sewage reached the maximum.