Study On Confluence Characteristics And Overflow Pollution Control Of Combined Sewer System In Urban Village In Coastal Shallow Hilly Region

At present,black-odor water is a major disease of urban environment in China.Due to the heavy rainfall intensity and high underground water level in coastal areas,and water from mountains and rivers are easy to gather in the shallow hilly areas,and the old facilities in urban villages are difficult to be transformed,the overflow pollution of combined sewer system is particularly serious.Zhuhai is a typical coastal shallow hilly city with a large number of urban villages.The paper takes the combined sewer system of Jiechong village,Zhuhai as the research object,the confluence characteristics and overflow pollution control of the combined sewer system in urban villages in the coastal shallow hilly area were studied.This paper analyzed the monitoring data of water quantity and quality to determine the confluence characteristics and existing problems of combined sewer system.The main problems were:low sewage collection rate,high pipe infiltration rate,insufficient flow capacity during rainfall,and low concentration of pollutants in storm runoff(only the concentration of SS is high).Based on the SWMM model in the MIKE URBAN software,a dynamic model of water quantity and quality was established,and the overflow pollution control strategy and effect analysis of the combined sewer system were carried out.Three control strategies were proposed:1)If pipeline control measures(optimize the interception ratio)were taken,based on the premise that the combined sewer system of Jiechong village contained areas where no sewage was collected and the pipeline infiltration rate was normal(20%),in order to make the annual overflow pollution load of the combined sewer system less than or equal to the annual storm runoff pollution load of the separate sewer system,the combined sewer system needed to meet the maximum flow capacity of 630m~3/h,then the interception ratio was about 4.5.2)If source control measures(sponge city)were taken,the total annual storm runoff volume control rate could reach 66.81%,which was 28.96%higher than that in the current situation,meeting the planning and design requirement.Based on the premise of different maximum flow capacities and normal pipeline infiltration rate,the reduction rates of annual overflow quantity and overflow pollution load were all high,meeting the requirement that the annual overflow pollution load should be less than or equal to the annual storm runoff pollution load of the separate sewer system.3)If storage measures(storage tanks)were adopted,based on the premise of different maximum flow capacities and normal pipeline infiltration rate,the storage tank volume could be designed in accordance with two different standards:the requirement that the annual overflow pollution load should be less than or equal to the annual storm runoff pollution load of the separate sewer system or the EPA(United States Environmental Protection Agency)planning and design standards of combined sewer system,determining the interception ratio after the storage tank was completed and put into operation.