The Research On Improvement Of Water Quality In Urban Second Water Supply System

The secondary pollution of drinking water in residential quater during transporting and storing up not only makes the tremendous economic losses of society, but also affects seriously the users' health. To solve the problem of secondary pollution has been the key to guarantee the quality of drinking water.The article takes the second water supply system of the special economic zone of Shenzhen as example, the research includes: status of second water supply; effects of reservoir material and hydraulic property; policy of second water quality control.In the examination of the examples, we find that the status of second water supply system in Shenzhen is not optimistic. The research indicates that the erosion, scale, propagation of microorganism, byproduct of chlorine residual, environment second pollution and seepage of reservoir are primary reasons of second water pollution.According to the research of byproduct of chlorine residual and biology film, beton is not an appropriate material for reservoir. For the reservoir of big volume, it is suggested to use beton with vitreous enamel dope. For the small reservoir, stainless steal, fiberglass or stain can be used.The limit of standing time in reservoir is raised by the results of mathematic model and hydraulic property. And then the material is decides accordingly. At the meantime, the water is made flow in reservoir with entering water or assist whirling fluid device.Use the method of CFD instead of pilot testing, Using Fluent software simulation can simplify the research and design of reservoir, we can also get the fluid distribution, in the simulation with different number of guiding plates, the results are similar with the ones of pilot testing. The simulations under different conditions show that increasing the number of guiding plates and inserting perforated plates, changing the shape of turner, enlarging inlet and outlet diameter can also improve the hydraulic efficiency.According to the research, the standing time is under 8h when the temperature is below 20℃, and is under 6h in the area where the temperature is over 20℃. The maximum standing time is under 12h.