Preparation And Characterization Of PVDF Composite Forward Osmosis Membrane By Interfacial Polymerization

Forward osmosis is new developing membrane separation processes in the recent years.Interfacial polymerization is the most effective and developmental future for preparation composite forward osmosis membrane.The poly(vinylidene fluoride)(PVDF)composite forward osmosis membranes were prepared in this paper.A nonsolvent thermally-induced phase separation(NTIPS)method was first proposed to fabricate hydrophilically-modified poly(vinylidene fluoride)(PVDF)support membranes to overcome the drawbacks of conventional thermally-induced phase separation(TIPS)and nonsolvent-induced phase separation(NIPS)methods.And a series of composit forward osmosis membranes were fabricated by the interfacial polymerization supported on hydrophilically-modified PVDF support membranes,and the relationship between performance and conditions of membrane preparation were discussed.The effects of testing conditions on separation property of membrane were studied.The PVDF/PVA support membranes and its composite forward osmosis membranes were tested in forward osmosis membrane bioreactor(OMBR),and their water treatment results were analyzed.The support membranes of composite forward osmosis membranes were studied.The property of the composite forward osmosis membrane was directly affected by the support membranes.In this paper,hydrophilically-modified PVDF membranes were successfully prepared by blending in hydrophilic polymer polyvinyl alcohol(PVA)and ?-caprolactam(CPL)at 140 oC.A series of PVDF/PVA blend membranes were prepared at different total polymer concentrations and blend ratios.As the total polymer concentration increased,the tensile strength of the membranes increased.Meanwhile,the membrane pore size,porosity and water flux decreased.With the PVDF/PVA blend ratio increased from 10:0 to 8:2,the membrane pore size and water flux increased.The dynamic water contact angle of these membranes showed that the hydrophilic properties of PVDF/PVA blend membranes were prominently improved.The higher hydrophilicity of the membranes resulted in reduced membrane resistance and,hence,higher permeability.The total resistance of the modified PVDF membranes decreased significantly as the hydrophilicity increased.The irreversible fouling related to pore blocking and adsorption fouling onto the membrane surface was minimal,indicating good antifouling properties.The PVDF composite forward osmosis membranes were prepared on the support of hydrophilically-modified PVDF membranes with m-phenylenediamine(MPD)as aqueous monomer and trimesoyl chloride(TMC)as organic monomer.The preparation conditions,such asmonomer concentration,curing temperature,and time of polymerization,were systematically studied.The results showed that with the PVDF/PVA blend ratio increased from 10:0 to 8:2,the polyamide surface of composite forward osmosis membranes showed more uniform and denser,and with lower structure parameter and high intercept performance.The optimum conditions were as follows: the reaction time was 5 minutes,the curing treatment temperature was 80 oC,the MPD concentration was 2wt% and the TMC concentration was 0.15wt%.The PVDF/PVA support membranes and its composite forward osmosis membranes were applied to the OMBR.For the problem of salinity accumulation in OMBR system,the support membrane and its composite forward osmosis membranes were used together in OMBR(UFO-MBR).The results showed that the accumulation of salinity in the UFO-MBR was controlled and the flux of the composite forward osmosis membranes was improved.The effluent CODMn from OMBR and UFO-MBR were essentially less than 3 mg/L.The turbidity of the effluent of the two systems was significantly lower than 1 NTU.The composite forward osmosis membranes,which covering with a dense skin layer,had efficient interception effect on organic pollutants.In UFO-MBR system,the PVDF/PVA blend membrane on the unsaturated structure of organic pollutants removal rate was low,while the removal rate of organic compounds with large conjugation system was higher.The combination of hydrophilic modified PVDF support membranes and composite positive permeable membrane can effectively improve the removal rate of ammonia nitrogen in OMBR system.