Studies On The Water Quality Safety And Residual Chlorine Control In Municipal Water Supply System

Along with the improvement of people's life, the growth of the social economy, and the carrying forward of the international process, the comprehension of the relationship between the health and the water quality is deepened continuously, and the safety of water quality draws so much more attention that it is becoming one of important topics on the water quality studies. Water quality safety includes the chemical safety and the microbiological safety. Although the chlorination is a crucial measure to ensure water microbiological safety, it produces carcinogenic disinfection by-products (DBPs) which reduce the chemical safety. So it is very important to study the residual chlorine, disinfection by-products and biological stability to enhance the water quality safety in municipal water supply systems.Applied the water quality data of recently years, by means of the cluster method, Xi'an water supply system's subregion was achieved successfully to analyze the water quality variation. The three-step screening method which includes variance analysis, combined evaluation index analysis and maximum irrelation analysis was established to get rid of the interference indexes in order to improve the cluster analysis result.Based on the water quality subregion of Xi'an water supply system, studies on the distribution and variation of DBPs and BDOC in water manifested that the level of DBPs were lower than the limit values in our national water quality standard, while the biological stability was poor so that enough residual chlorine should be needed to guarantee the water quality. In addition, through analyzing the change of BDOC in water treatment processes, pipelines and static experiment, the BDOC variation course in water supply system could be divided into eight stages in view of the mechanism which the variation regularity and reason had been provided.The static experiment analysis indicated that there were two types in the residual chlorine static decay process, one-stage and two-stages. According to the decay rate, the two-stages type had two categories as large-small type and small-large type. The separating time of two-stages wasn't a fix value which it was influenced by the factors such as the initial residual chlorine concentration, the total organic carbon and so on.Based on the principle of joint flow conversion, the theoretical derivation proved that the flowing time of a simplified water network was inconsistent with the actual flowing time. So it was suggested that a flowing time conversion coefficient should be introduced in water quality dynamic modeling in water distribution system.From the causes of the residual chlorine decay in water supply system, its model was decomposed as the product of the initial residual chlorine concentration and some factors which included the bulk decay factor, the mass transfer factor, the corrosion factor, the diffusion factor and the detachment factor. This kind of decomposition would be conductive to comprehend the residual chlorine decay mechanism and to solve the dynamic model.Through the continuously monitor and water flow tracking tests in the westward water supply pipelines of QuJiang water plant, the residual chlorine dynamic model was established and well confirmed. Employing this model, the lowest delivery residual chlorine concentration of the QuJiang water plant was forecasted to reasonably control the chlorine addition, which the expression wasThis study is financially supported by Shaanxi Natural Scientific Foundation. Project name: Online management and optimization of water distribution networks equipped with Supervisory Control and Data Acquisition System (SCADA) System. Project number: 2003E₂21.