Research On Operation Process And Purification Effect Of Treating Luan River By Ultrafiltration Membrane

With the progress of human civilization, population growth and rapid development of industry and agriculture, the issue of drinking water quality becomes more prominent. On one hand, drinking water quality of source water is deteriorating and users share higher requirements for drinking water; on the other hand, water resources distribute uneven in time and space. Both sides stimulate the development of the water treatment technology and the improvement of water quality standards. In China, with the promulgation of the new standards for drinking water quality (GB5749-2006), the demand for water quality becomes higher, and therefore, to some extent, the traditional water treatment process cannot meet the demand of the drinking water quality standards. In order to meet the standards, it is necessary to probe into the improvement of traditional process and the application of new technology.Ultrafiltration as an emerging water treatment technology has not yet been widely applied to waterworks because of membrane fouling and insufficient knowledge of the adaptability of ultrafiltration membrane to various waters in China. In order to detect whether or not the combination of ultrafiltration technology with the existing process in waterworks can guarantee membrane treated water quality and the economy, reliability of the process in treating Luan River, the experiment introduced ultrafiltration membrane to the existing coagulation, sendimentation and sand filter process in waterworks. Experiments lasted one year and experienced three water quality periods, namely, high temperature and algae period, normal water quality period & low temperature and turbidity period. The operating conditions of coagulation—sendimentation—ultrafiltration membrane and coagulation—sendimentation—sand filter—ultrafiltration membrane processes in different water quality periods were systematically studied. The research was on regular indices and non-regular indices in membrane feed water and treated water, the molecular weight distribution of membrane feed water, treated water and membrane backwash water, distribution and concentration of disinfection by-products and their precursors, membrane running cost, operation stability and so on. The conclusions were made based on the research:the existing buildings of waterworks could be fully utilized, and simultaneously the membrane treated water quality was effectively guaranteed and the ability to resist the change of water quality load was stronger, the related parameters were as follows:The optimized operating parameters of the first process during different water periods were as follows. In the high temperature and algae period, the flux was 60 L/h-m2·mH2O, filtration time 30 min, and backwash chlorination 2 mg/L. At the normal water quality period, the flux was 50 L/h-m2·mH2O, filtration time 30 min and prechlorination concentration 1.2 mg/L. As for alleviating membrane fouling, the effect of adding coagulant aid HCA to reaction tank was better than without adding and the effect of addition of sodium silicate was worse than without adding. At low temperature and turbidity period, the flux was 50 L/h·m2·mH2O, filtration time 30 min, prechlorination concentration 2 mg/L and the chemical NaClO. For the second process, the operating parameters were as follows:at low temperature and turbidity period and normal water quality period, the operating parameters were exhibited, Flux was 60 L/h·m2·mH2O, filtration time 30 min and prechlorination concentration 1 mg/L. During high temperature and algae period, the flux was 75 L/h·m2·mH2O, filtration time 20 min, the operation modes were prechlorination and CEB, the CEB time 0.5 h and the CEB cycle 24 h; the CEB chemical was NaClO and prechlorination concentration was 0.5mg/L.As for the water quality indices of membrane treated water in the first process, CODMn and UV254 were higher than that in the second process, but turbidity was contrary. Turbidity values were all smaller than 1 NTU. Except that some of the total bacterial colony number and total coliforms exceeded standards for the first process, other indicators were all better than the demand of the standards. The dissolved organic matter (DOM) in treated water of ultrafiltration membrane was mainly small molecular weight DOM, similarly, this part DOM contributed the greatest contribution to UV254, trihalomethane formation potential (THMFP) and haloacetic acids formation potential (HAAFP).The longer the filtration time was, the faster TMP increased at the beginning, the shorter the filtration time it took to reach stabilization, the longer it took for backwash transmembrane pressure (BTMP) to reach a steady decay, and BTMP was smaller. With the extension of the filtration time, the values of turbidity, CODMn, UV254 and THMFP in backwash water increased, but the change of time had little effect on THMFP and UV254. Most of the DOM in MBW distributed in more than 30 kDa and less than 1 kDa, but for UV254, it was mainly distributed in the range of less than 1 kDa. The fractal dimension of flakes in MBW had a good linear relationship with filtration time. Temperature greatly affected the CODMn in backwash water of the second combined process. The increase of temperature led to increased CODMn value, but it had a little influence on turbidity and UV254 in MBW.The membrane water productivity, power consumption for specific water production of the process when treating the sand filter were better than that of the process treating sedimentation tank produced water, but it was contrary with power consumption for specific water production.