Hydrophilic Modification Of PVDF/loofah UF Membrane To Improve Antifouling Performance Based On Wastewater Recycling

In recent years,polyvinylidene fluoride(PVDF)has been widely applied in water treatment as a main material of ultrafiltration membrane.However,it has been limited because the hydrophobicity of PVDF makes membranes susceptible to fouling.Therefore,hydrophilic modification of PVDF membranes was widely recognized as an effective way to reduce the membrane fouling.Besides,the loofah sponge belongs to renewable green resources,and it shows excellent anti-fouling performance in oil pollution.In this paper,the lithium chloride/dimethyl acetamide(Licl/DMAc)was selected as solvent,and the orthogonal experiment was designed to investigate the solution condition of loofah sponge.The PVDF/loofah fiber UF membranes were modified by controlling the content of loofah fiber,polyvinyl alcohol(PVA),polyethylene glycol(PEG)and PVDF in casting solution from the aspects of membrane morphology and structure and hydrophilicity.In addition,the membrane fouling experiments of typical foulants and the effluent of secondary treatment were perfomed to assess the antifouling performance of modified membranes.The main results were shown as follows:(1)As the results of orthogonal analysis,The optimum solution conditions of loofah fiber were obtained at 6%LiCl,10 h the stirring time at room temperature,80℃ heating temperature with 2h heating time.(2)The PVDF/loofah ultrafiltration membranes were prepared through blending method.The addition of loofah fiber showed less influence in membrane porosity,but significant effect on the structure of membrane surface and section.At the same time,the hydrophilicity of the membranes has been improved in terms of water contact angle measurement.With the content increase of loofah fiber from 0% to 2.0%,the membrane flux increased from 58.7L/m2 h to 182.6L/m2 h when PVDF was 14%,and from 75L/m2 h to 257.7L/m2 h when PVDF was 16%.Nevertheless,the rejection rate of bovine serum albumin(BSA)of the prepared membranes were maintained all above 92%.The addition of loofah fiber could improve the membrane fouling resistance significantly,and when the content of PVDF and loofah fiber was 16%,1.2% respectively,the membrane was highest,increasing from 49.85% to 94.19%.(3)Blending and copolymerization of PVDF/loofah and PVA have been successful approached,and the PVDF/loofah membranes have been effectively endowed with high and durable hydrophilicity by controlling the content and degree of polymerization.The lower the polymerization degree of PVA,the higher the hydrophilicity of modified membranes.When the ratio of PVDF:PVA was 4:1,the water contact angle of membrane that added PVA2488,PVA1788,PVA0588 was 93.4°,66.5°,28.8° respectively.Besides,the membrane flux recovery rate under the PVDF: PVA ratio of 4:1 was higher than PVDF:PVA of 8:1 during the membrane fouling experiments of BSA.Considering the membrane properties and the performance parameters,the PVDF/loofah membranes could achieve better effect when the ratio of PVDF: PVA1788 was 4:1.(4)The morphology and structure of PVDF/loofah/PVA flat UF membranes were optimized by the addition of PEG to the casting solution.Based on the scanning electron microscopy(SEM)images,PEG has obvious effects to the membrane pore formation.With the increase of the content of PEG,the microporous on membrane surface increased obviously as well,in addition of bigger aperture of support layer and thinner of the skin layer.The hydrophic membrane flux and rejection of BSA were all increased first then decreased with the increase of PEG content.When the addition of PEG content was reached to 2%,the membrane showed higher flux,at the same time,the rejection rate was the highest.Furthermore,the antifouling performance of the modified membrane can be achieved when PVDF content was 14% and PEG content was 2%.(5)The antifouling performance of modified membranes was analyzed in terms of hydrophilicity and morphology structure.It is found that the hydrophilic components are more likely to cause membrane fouling than the hydrophobic components in the process of simulating the wastewater with different ultrafiltration membranes.The membrane flux was decreased rapidly and the pollution was more serious than that of the simulated wastewater by using the self-made ultrafiltration membrane to treat the effluent from the two stage effluent treatment.