Macro-Assessment And Micro-Analysis Study Of RDII Of High Level Sewer Network In Lowland Urban Area

Sewerage network is an important infrastructure for cities,which is responsible for the collection of urban domestic and industrial wastewater and is the"vein"of the city.Many problems will be encountered in the process of sewage network operation,among which,the Rainfall-derived inflow and infiltration（RDII）problem affects the normal operation of the sewage collection system and treatment system,increasing the operating load of the sewage network and reducing the pollutant treatment rate of the sewage treatment system,which is an important problem that needs to be solved in China.The problem of RDII is particularly significant in the plain river network cities due to the high groundwater level and abundant rainfall.For this reason,this paper carries out research on the RDII problem of high-level sewerage network in plain river network cities based on the idea of layer-by-layer analysis from macroscopic assessment at large and medium scales to microscopic analysis at small scales,and the main findings of this paper are as follows:（1）At the level of large scale assessment of the collection capacity and efficiency of drainage system facilities,a typical plain river network city J is used as an example to carry out large scale assessment,and two capacity assessment indexes,drainage pipe density and drainage pipe coverage,are proposed;in terms of collection efficiency assessment,the rate of change of water quality is proposed,and the relationship between water quality index i（i∈｛BOD,COD,NH₃-N,TN,TP｝）and rainfall is established,and the larger the value,the more serious the problem of the system being invaded by rainwater.In addition,according to the cross-sectional comparison of the five water quality indicators,it is found that ammonia nitrogen is a good choice for value calculation.（2）In the medium-scale assessment of the collection capacity and efficiency of drainage system facilities,a wastewater treatment plant P-1 was selected as the object of study,based on daily water quality monitoring data to carry out a more detailed assessment and analysis,summarize the water quality changes in the treatment plant,and refine the coefficient describing the relationship between water quality indicators and daily rainfall,the larger the value,the more serious the system RDII problem.Based on the calculated values of the influent water quality in the east and west areas of the P-1 wastewater treatment plant,a comparison shows that both drainage systems have serious RDII problems,and the west pipe network is more serious,and the drainage system of P city is in urgent need of quality and efficiency improvement.（3）In the small-scale RDII analysis of the high-level sewage network,firstly,we summarize the operation rules of the DS sewage system operating at high level,and screen out the level and conductivity monitoring data that are more advantageous for RDII assessment of this type of drainage system.conductivity difference,and summarize a set of process methods applicable to RDII assessment and location of wastewater pipe networks operating at high liquid levels,which provides reference for RDII assessment of the same type of drainage networks.