Empirical Research On Combined Sewer Overflow Control Method Based On Watershed Perspective

In recent years,the urban wastewater treatment plant(WWTP)has achieved remarkable results in improving the quality and efficiency in China.On the one hand,black-odor river has been basically eliminateas well as the efficiency of urban domestic sewage collection and treatment has been significantly improved.On the other hand,the problem of "returning black-odor river " caused by combined sewer overflow(CSO)in rainy days is prominent.Although CSO control has become the "standard" for water environment governance in most cities,and some cities have achieved good results,the CSO control standards are not perfect,the "plant-sewerriver" capability is difficult to match,and the performance evaluation is unreasonable.However,such problems cannot be solved in the short term,and the effectiveness of urban CSO control still needs to be improved.This paper uses the method of literature research,data comparative analysis to sort out and summarize the control standards,engineering technology and government supervision of CSO in developed countries.Taking King County in the United States as an example,the composition of the CSO control system including the pipe network system,CSO treatment plant,and sewage treatment plant in the service basin of the West Point Sewage Treatment Plant is introduced in detail.A systematic analysis was made on the systematic operation process,discharge standards and government performance supervision of the West Point WWTP,focusing on the rainy day operation mode,capacity maintenance,discharge standards,monitoring reports,etc.In order to provide reference for urban CSO control engineering practice and river basin water environment management in China.Based on the above research,this paper proposes a set of CSO event division,regulation and storage treatment facility layout and scale determination by means of data statistics and model simulation,taking into account factors such as rainfall characteristics,“plant-sewer” operating condition matching,and CSO control effect.,Control effect monitoring and evaluation methods.Taking the Qingshui River Basin in Guyuan City as an example,through model construction,simulation analysis of measured data and calibration verification,it is determined that the minimum inter-event time(MIET)for dividing independent rainfall events is 12 hours,and the MIET for dividing CSO events is 12 hours.The location and scale of the CSO storage(166,000 m~3)were determined with the target of4 times/year of annual overflow for each CSO overflow.The corresponding annual CSO volume control rate was 71.7%,and the annual average reduction rate of total pollutants is SS89.0%,COD75.5%,TN62.8%,and TP54.1%.The key monitoring points of the pipeline network for real-time control of the operating conditions of the CSO storage tank and the sewage treatment plant are proposed.The CSO effect evaluation monitoring point layout plan was clarified.The monitoring indicators as well as the sampling and calculation methods have been determined.