A Study Of The Application Of System Dynamics Model On CSO Pollution Control

Rapid development of cities requires improvement of city drainage system. Nevertheless, some of the existing urban drainage systems still belong to the combined sewer system. Combined sewer system may cause overflow pollution in the rainy days and have certain impact on receiving waters. In this paper, we mainly established a dynamic model of combined drainage pipeline network system by combining an investigation on a market-town combined sewer system in Chengdu. By changing the model parameters, we performed simple research and discussion on the overflow pollution control measures of the whole combined sewer network. The specific research results are as follows:(1) By comprehending the concept and structure of the system dynamics and combining the characteristics of combined sewer system, we established a dynamic model of a market-town combined sewer system in Chengdu, analyzed the basic structure of the model, and divided the market-town sewer system into five subsystems:pollution source subsystem, collection subsystem, treatment subsystem, overflow subsystem and receiving water subsystem.(2) We performed investigation and research on the market-town drainage system in Chengdu mainly by means of monitoring the selected main canals and the overflow vents. Through investigation, we concluded that the market-town had a large number of overflows after entering flood season. A large amount of sewage was directly discharged into the downstream connecting agricultural irrigation channel and eventually into the river, causing water pollution. We performed simulation research with the established system dynamics model.(3) Through the system dynamic model, we simulated variation trends of COD and two water pollutants ammonia and nitrogen. According to the simulation, we found that the variation of COD, ammonia and nitrogen were basically identical in simulated surface runoff and overflow. They all increased along with rainfall intensity, which mainly because the increase of rainfall intensity caused the increase of overflow intensity as well as the increase of pollutant concentration.(4) We validated the simulated data of the established system dynamics model with monitoring data from the market-town sewage investigation and concluded that the pollutant variation trend of the combined sewer system of the system dynamics model basically conformed with the actual variation trend.(5) We performed research on the application of the pollutant control scheme using parameters variation of the system dynamics model and found that pipeline flushing had no obvious effect on overflow sewage volume but had significant effect on pollutant removal, which meant that pipeline flushing could be used as the main control measures to combined sewer overflow pollution. In the meanwhile, we found out through research that the overflow pollution control scheme could be implemented by combining several schemes.