Abstract
Detention tank is widely used in urban waterlogging control, rainwater runoff pollution control, combined sewer overflow (CSO) control and rainwater utilization, etc. For detention tanks in different types or functions, their design methods, construction forms and ways of operation and management are very different. In recent years, many cities in China have begun to apply or plan to build CSO detention tanks to control the CSO pollution, but there are still many problems and puzzles in designing the tank. This paper summarizes and evaluates the common design methods of CSO detention tank at China and abroad. Based on the physical projects in which the author has participated in, the scale and control effect of the CSO detention tank are studied by model simulation, taking a combined sewer system catchment in the Beijing old city as examples. Based on the analysis, the long-term simulation method is recommended for designing of CSO detention tanks in China, and a design criteria suitable for a larger range can be determined through research and analysis of a typical and representative area if there is no way to research every area. At last, several key factors that affect greatly the scale and pollutant control efficiency of CSO detention tank are summarized and analyzed, including objectives of CSO control, rainfall characteristics, CSO pollutants transport law, interception multiple, capacity of wastewater treatment plant, space conditions and investment, layout of detention tank and operation mode of detention tank. Hope to provide reference for the scientific designing of CSO detention tank and realize cost-effectively controlling CSO in cities of China.
Highlights
The calculation formula of scale design of combined sewer overflow (CSO) detention tank has been provided in the relevant Codes [2], the formula is difficult to meet the actual needs of the projects since the CSO detention tank scale design and control efficiency of CSO pollutants are affected by a lot of factors, besides, there are huge variations in different cities in China
The scale of CSO detention tank is designed according to a relatively clear control objective, such as overflow frequency, overflow amount, CSO amount control and control rate of CSO pollution load, by modeling the drainage network, or by simulating and analyzing a typical area and drawing up correlation curves between the detention amount and control efficiency to choose a rational scale for the detention tank
This paper summarizes the design methods of CSO detention tanks adopted in the United States, Germany, Japan, Italy and some Chinese cities
Summary
CSO pollution status and control objectives directly affect or determine the scale of CSO control measures. The design of the tank scale is usually based on CSO control objectives in some countries. Many cities in China have not yet formulated a clear goal of CSO control, which affects the formulation of CSO control plan and the determination of the scale of detention tank [7, 8]. The CSO control objectives in developed countries include reduction of overflow in amount and times, reduction of total overflow pollutants, control of rainfall events in a certain recurrence period, or "combined sewer system pollution load equals to that of separate sewer system", all of which are based on achieving or upgrading the water quality of the receiving water to a certain target.
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