Study On The Change And Control Of Disinfection Byproducts In Drinking Water Supply System In Xi'an City

The control research of disinfection by-products in drinking water is a focus of water-treatment field in recent years. The by-products of the chlorination are brought out while it is disinfecting drinking water. Nowadays chlorine disinfection is the most popular disinfection treatment in the world. So it is important to study the formation, variation and control means of DBPs in different water environment.In this paper, detected the water quality variation such as organic matter, trihalomethanes, precursors of trihalomethanes, algae and so on during water treatment process in Qujiang and Nanjiao waterworks and during the water distribution system. Then enhanced coagulation through orthogonal test and single factor experiments was made to find the best enhanced coagulation condition for Xi'an city.Monitoring results showed: THMs was not detected in Xi'an source water. It was formed in water treatment process. CHCl₃ and CHCl₂Br dominated THMs. The concentration of THMs in treated water was about 4～17μg/L. The removal rates of THMs precursors in conventional water treatment process was about 40%. The removal effect of THMs was almost zero. THMs' formation was obvious. Pre-chlorination, post-chlorination and hydraulic residence time were the main influencing factors. Pre-chlorination was the main reason for THMs formation during water treatment, which contributed about 50% to THMs. THMs in water distribution system were crescent, the increasing rate of speed gradually became slowly. The concentration of THMs in some water supply network could be up to 25～30μg/L. As one of the most important source, the detected algae in source water of Xi'an were Bacillariophyta, Chlorophyta, Cyanophyta, Euglenophyta, and Chrysophyta. Bacillariophyta and Chlorophyta were the main algae, respectivlly about 70% and 20%. The amount of algae in treated water was about 2 million per litre. Experiment results showed: The main influencing factors of the enhanced coagulation included types and dosages of coagulant, pH, chlorine dosage and the condition of hydrodynamic mixing. Coagulant dosage and pH were the most important factors to enhanced coagulation. After adding chlorine to water, increasing the mixing speed was rather important. The effect of mixing speed during 250～400r/min was little, but the time of mixing was important. The perfect time was 30 seconds. The best enhanced coagulation condition of the test was chlorine dosage 0.8mg/L, pH 8, hydrodynamic condition d plan, PAC dosage 25～30mg/L and PAFC dosage 30mg/L. The coagulant effct of PAFC was better than PAC.