Treatment And Practice Of Drinking Water By Membrane Separation Technology

With the rapid development of our country industry and agriculture, the constant expansion of the urban construction, the demand for fresh water resources has increased dramatically, but due to various pollution water continuously contributed to the lack of the contradiction between supply and demand of water. At the meantime, the new Drinking Water Standard proposes higher demand for drinking water treatment by strengthening requirements in water quality index, including organic matters and microorganisms. Facing increasingly stringent drinking water quality standard and severe water pollution, there is urgent need for the renovation and update for most of the drinking water treatment plants in China.Membrane technology has the advantages of high performances, low energy consumption, non-phase transition, non-pollution et. ac, as compared with traditional separation techniques. Therefore, membrane separation has been widely applied in various industries, and shows promising prospect in the field of environmental protection, including that of water and wastewater treatment.Based on an updated water treatment plant in Laibin, Guangxi Zhuang Autonomous Region in China, performances of ultrafiltration-based membrane technique were studied, following technique of chemical coagulation under typical conditions, by conducting bench-scale and pilot-scale in this paper. The feasibility of ultrafiltration-based membrane technique as an alternate of traditional sand filter was also analyzed from technical and economical viewpoint.Results of bench-scale experiments shows that, flocculation process effluent turbidity range in 2~10 NTU, ultrafiltration process can consider to use cheap PVC(polyvinyl chloride) ultrafiltration membrane, PVC is suitable material for ultrafiltration because of its cost-effectiveness. However, under the condition of higher influent turbidity or membrane fouling, PVDF-based ultrafiltration with the performance of high pollution resistance should be chosen. Considering typical turbidity after coagulation in this WTP, PVC-based ultrafiltration was chosen in the following tests.Results of pilot-scale experiments shows that, turbidity in the effluent after ultrafiltration was lower than 0.2 NTU, well below 1 NTU regulated by the new Drinking Water Standard, with removal efficiency of more that 97%. Since most of turbidity is caused by suspended solids(SS), obviously, ultrafiltration presents a stable removal performance for SS.The overall water purification performance by ultrafiltration is superior to that of traditional sand filter. This lies in that: ⑴turbidity in the effluent after traditional sand filter is significantly influenced by influent turbidity, while influent turbidity has little effect on the removal performance of ultrafiltration. ⑵the average CODMn removal efficiency was 38%, about 26% higher than that of sand filter. The average UV254 removal efficiency was 26%, about 14% higher than that of sand filter. The average removal efficiency of ammonia nitrogen was 34%, about 23% higher than that of sand filter. With regard to micr⑶ oorganism index, total coliforms bacteria in the effluent after sand filter occasionally were above the limits with shock load, while removal of microorganisms was hardly influenced by such factors as high temperature and rainfall.Due to the natural organic matter(NOM) content in the raw water is low,plus after Organic matter in suspended and colloidal state has been effectively removed after pretreatment, including coagulation and clarifier, and dissolved organic matter is predominant in the effluent. On the other hand, ultrafiltration is characterized by cutting colloids and organic compounds with high molecular weight but comparatively poor retention, especially for dissolved organic matter with low molecular weight. So the ultrafiltration membrane for CODMn, UV254 and other organic material removal rate is relatively low.The Qingshui River is typical southern water quality characteristics, obvious seasonal characteristics, high temperature and much rainfall with high turbidity and high incidence of algae. With the increase of water consumption and the constant improvement of water quality detection with strict, waterworks is faced with expansion and the technological transformation. Flocculation- ultrafiltration membrane system in the sensory properties and general chemical indicators, microbiological indexes and organics indexes showed good purification effect; In water at the same time, on the basis of the expansion of the reform of capital construction cost, combined with the characteristics of ultrafiltration membrane system, of coagulants/flocculants, disinfectant dosing dosage, adjust measures to local conditions of the optimization of the overall construction costs, optimization can be used as water treatment plant expansion plan.Membrane fouling is main problems in the application of membrane technology. Through the improvement of membrane materials properties, take the appropriate pretreatment method, the reasonable way of membrane cleaning, etc., Can effectively control membrane pollution, increase the use of membrane cycle, and guarantee the stability of the membrane in practice operation. Membrane fouling mechanism is complex; need further exploration, in order to more effectively guide the engineering practice of water treatment.