Preparation Of Polyphenol-metal Complex Modified Membrane And Its Manganese Removal Performance

Membrane separation technology is one of the most effective methods of alleviating water shortage,but membrane fouling reduces the separation efficiency and seriously restricts its application in water treatment.Manganese widely exists in the environment,but the overdose of manganese in drinking water may threat to people’s health.In this work,modified membrane was prepared by coating the solution of tannic acid and ferric chloride layer by layer onto the surface of PVDF microfiltration membrane,and its antifouling and manganese removal properties were investigated.Permeation and selectivity properties showed that layer by layer method can successfully coat polyphenol-metal complex film on the surface of PVDF membrane.After optimization,the optimum coating method and concentration were determined as TA 4g/L-Fe 1.9g/L.Membrane surface characteristics showed that the increasing TA-Fe coating layers led to the increase of the content of tannic acid on the surface of modified membrane,and the enhancement of hydrophilicity and selectivity property,while the surface roughness did not change significantly compared with the base membrane.Negative surface charge of the surface of single layer and double layer coating modified membrane was enhanced in the range of p H=3-10.The rejection rate of humic acid（HA）,bovine serum albumin（BSA）,E.coli and Mn O₂ colloidal particles with negative charge was increased by electrostatic repulsion.The retention of pollutants could also be enhanced due to the increase of filtration resistance of the three layers coating modified membrane.During ultra-low pressure pollution filtration of humic acid solution,bovine serum albumin solution and E.coli solution,which were used as model pollutants,at 1500 Pa,the specific flux decrease of polyphenol-metal complex coated membrane was less than that of PVDF,which proved that the modified membrane had better antifouling property against humus,protein and microbial contaminants.XDLVO theory and classical membrane pollution model were used to analyze the antifouling mechanism.The main antifouling mechanism of the modified membrane was that the hydration film was formed on the surface of the membrane due to the enhancement of hydrophilicity and the enhancement of electrostatic repulsion force due to the increasing negative charge by polyphenol-metal complex layer,thus hindered the adhesion of pollutants to the membrane surface.The modified coating layer can inhibit the growth of microorganisms and reduce the microbial fouling on the membrane,which was confirmed by the result of CLSM after E.coli fouling.Due to the increased negative charge and phenol hydroxyl group of the coating layer of the modified membrane,at the initial stage of filtration under 600 Pa,the retention rate of the modified membrane to the Mn²⁺ions were 90.5%,50.9%higher than that of PVDF.The retention rate of the modified membrane to Mn O₂ colloidal particles under 1500 Pa was 87.6%,while 69.0%for PVDF.In the short time periodic operation of the actual water containing manganese,the flux decrease of the modified membrane was lower,which illustrated the better antifouling property of the modified membrane.The turbidity,manganese content and ATP content of the effluent of the modified membrane were also lower than that of PVDF.In the process of long-term operation without cleaning after pre oxidation,the final stable flux of the modified membrane is higher,and the performance of removing manganese and organic matter is improved compared with that of the base membrane.Manganese content of effluent of both modified and unmodified membrane were lower than the limit value of GB5749-2006.The results show that the membrane modified by polyphenol-metal complex has application prospects in the treatment of manganese containing water with complex composition.