Research On The Preparation And Anti-pollution Performance Of The EVOH Membrane And The Modified EVOH/PVDF Membrane

With the increase of population and the acceleration of industrialization,the situation of water pollution has become more and more serious.Membrane separation technology is often used to treat sewage.However,the membrane separation technology has membrane fouling in water treatment and membrane fouling on the membrane surface,which has become a key factor restricting the further development of membrane separation technology.Researchers have delayed film fouling by means of hydrophilic modification of the membrane,but this method often suffers from chain instability,group shedding and other problems that cause the membrane to lose functionality.Therefore,in this study,the membrane elements were prepared by blending hydrophilic materials,and the anti-contamination performance was examined while ensuring the mechanical strength.Ethylene vinyl alcohol（EVOH）has both hydrophilic and hydrophobic groups and is widely used.In this study,hydrophilic EVOH membrane was prepared by immersion phase conversion method,and the main factors influencing the separation performance and mechanical properties of the films were examined by single factor tests.Finally,the optimal working conditions for the preparation of hydrophilic EVOH membrane were as follows:EVOH concentration 20%,magnetic stirring time 8 hours,casting liquid temperature 60°C,coagulation bath temperature at room temperature（15°C²0°C）.Through the detection of the surface morphology,XRD,water contact angle and maximum pore size of the membrane by scanning electron microscopy,the test results show that the EVOH membrane has high hydrophilicity.The mechanical properties of the EVOH hydrophilic membrane are poor,the mechanical strength was 80N,and the elongation at break was 15.47%.Therefore,the membrane is modified with PVDF to improve its mechanical strength.Through single factor tests,the main factors affecting the separation performance and mechanical properties of the membrane during the membrane manufacturing process were investigated.Finally,the total EVOH/PVDF mass fraction was determined to be 20%,and the M_（EVOH）:M_（PVDF）blend ratio was 8:1,the stirring time was 15 h,the casting solution temperature was 60℃,and the coagulation bath temperature was room temperature（15℃²0℃）conditions are the optimal conditions for preparing hydrophilic EVOH/PVDF blend membranes.The mechanical strength of the membrane was 113N,the elongation at break was 9.72%,and the mechanical properties of the membrane were greatly improved.In order to investigate the anti-pollution properties of the membranes,membranes were subjected to typical contaminant tests of bovine serum albumin（BSA）,polysaccharide（SA）,and humic acid（HA）membranes,membrane flux recovery assays,and sequencing batch bioreactions（MSBR）pilot test.The test results showed that the membrane fouling was mainly caused by the blocking of membrane pores,the formation of mud cake layer on the membrane surface and the compaction of the membrane.Physical washing can only wash away surface contaminants.Chemical cleaning and ultrasonic cleaning can wash out membrane pores.Membrane flux recovery rate of up to 90%.Through the MSBR pilot test,both membranes have a turbidity retention of more than 97%in the MSBR reactor,EVOH membranes reach 40 days in the use cycle,the blend membrane can reach 45 days,and have higher anti-pollution effect.