Pilot-scale Study On Membrane Fouling And Cleaning Of Drinking Water Treated By Ultrafiltration

With the increasingly stringent drinking water standards and the deterioration of drinking water sources, the traditional drinking water treatment process is difficult to meet the requirements. Ultrafiltration water treatment technology turns to be the leading technology used to treat drinking water, but membrane fouling and which resulting in increasing operation costs and shorting membrane life span come to be its shortcomings. A pilot-scale test carried out on Luan River raw water, membrane fouling factors and cleaning methods were studied.The sedimentation pond water treated by hollow fiber ultrafiltration membrane was studied, the results showed, during the long-term continuous operation, the treated water quality was superior to the Standards for Drinking Water Quality (GB5749-2006), stable and safe. The membrane used to treat sand filter water was better than used to treat sedimentation pond water.Considering water quality and operating conditions, based on ultrafiltration process transmembrane pressure, decreasing rate of membrane specific flux (SF) and decay rate of SFσ, membrane fouling factors were studied. Membrane inlet water quality, coagulation species and dosage, membrane flux and ultrafiltration period, pre-chlorination and or chlorinated backwash water, dosing activated carbon in raw water etc. were the factors which influence membrane fouling rate. The main conclusions are as follows: during different duration of water quality was that: low temperature and turbidity > abnormal temperature and turbidity > high temperature and algae. Coagulant constituted by FeCl3, PAC and HCA which membrane flux rate is lower than coagulant constituted by FeCl3, PAC and Sodium. With the increasing of SF filtration time extension during one period, decreasing rate of membrane specific flux (SF) and decay rate of SFσspeeded, and membrane fouling becoming serious. Pre-chlorination water membrane fouling was faster than chlorinated backwash water case. Dosing appropriate amount of activated carbon (5mg/L) help to reduce membrane fouling, however, excessive dosing (10mg / L) will speed up the membrane fouling.The effect that using physical cleaning, alkaline chemical cleaning and off-line chemical cleaning to control membrane fouling were studied, results showed, backwashing could reduce transmembrane pressure, but the reduction was limited. In process of flux maintenance, membrane equipment was used to treat sedimentation pond water, during abnormal temperature and turbidity high temperature and algae period alternate NaClO medial immersion with HCl lateral immersion, during low temperature and turbidity period using NaOH medial immersion combined with HCl lateral cycling. When the equipment used to treat sand filter water, NaClO medial immersion performed better. Overall, medial immersion has advantages over lateral washing. Transmembrane pressures were reduced to different extents, no matter using NaOH, NaClO, HCl or citrate alkaline chemical cleaning. Alkali washing is better than acid washing in removal of organic. Acid washing is better than alkali washing in removal of inorganic. Membrane inorganic ionic fouling mainly caused by magnesium, calcium, iron, aluminum and silicon. X-ray diffraction results showed, the major irons that cause membrane fouling were aluminum ion and silicon ion. Aluminum ion could be removed by chemical cleaning; however some silicon ions and iron ions couldn't be removed by chemical cleaning, which caused irreversible membrane fouling.Membrane equipment operating costs and stability were analyzed, the results showed, in the stage ultrafiltration membrane was used to treat treatment sedimentation pond water, processing per cubic meter water, the average pharmacy costs was 0.140 yuan, the average electricity costs was 0.082 yuan, the average membrane depreciation expense was 0.058 yuan, the average total costs was 0.280 yuan. In the stage ultrafiltration membrane was used to treat sand filter water, processing per cubic meter water, the average pharmacy costs was 0.021 yuan, the average electricity costs was 0.103 yuan, the average membrane depreciation expense was 0.045 yuan, the average total costs was 0.169 yuan. During the process there was 26 times breakdown, membrane equipment itself failure frequency only was 5%, other failures were occurred in the ancillary facilities. The membrane system could be a good guarantee on the overall stability of the process.