Hydrophilic Modification Of Ultrafiltration Membrane By Using Nano-size Materials Embedment And Characteristic

Polyvinylidene fluoride?PVDF?ultrafiltration membrane has been obtained increasely concerns and widely used for water and wastewater,due mainly to its high thermal and mechanical stability and chemical resistance.However,the intrinsic surface charge and strong hydrophobic properties of PVDF resulted in severe membrane fouling and permeability loss during its application,which inevitably reduce membrane spanlife and increase the maintenance cost.Membrane surface hydrophilic modification has been deemed as one feasible way to mitigate fouling problems in PVDF.Hence,in the present work,three nano-size materials,i.e.,nano-alumina,nano-titanium dioxide and graphene oxide were used respectively to blend into PVDF membrane surface during membrane fabrication.In contrary to conventional PVDF membrane,these modified UF membrane have stable antifouling capability with high hydrophilicity surface during treating real sewage in an MBR.The obtained results herein give new insight to the fouling mitigation and control in MBR and provide technique guideline for modified PVDF application.Firstly,PVDF/TiO₂ and PDVF/Al₂O₃ UF membrane were prepared by in-situ embedment methods during PVDF membrane fabrication,and the modified membrane performances,including filtration performance and surface properties were investigated The results displayed that the embedment of nano-particles increased membrane hydrophilicity,and then improve the membrane permeability without impact the organic rejection capabilities.From the direct SEM observation,the modified membrane embedded with nano-particles had a comparable dense and finger-like structures with PVDF membrane,where nano-size TiO₂ and Al₂O₃ were uniformly dispersed on its surface and rarely affect the membrane morphological characteristics.PVDF/GO ultrafiltration membranes were prepared by in-situ blending of GO nanoparticles into PVDF membrane.The SEM observation results demonstrated that the effective pore on the modified UF membrane were increased and the finger-like structure of the membrane cross-section were enlarged significantly,resulting to eventually increasing of membrane permeability.The fabricated PVDF/GO membrane has a high hydrophilicity,but the membrane rejection capabilities declined in bovine serum albumin and polymeric organic matters,since its high flux under the same driving force and low total resistance during filtration.Excellent ultrafiltration membrane were selected to evaluate membranes anti-fouling and anti-biofouling propensities.During the filtration of organic substances including humic acid,protein and polysaccharide,by using these modified membranes,their membrane fouling,especially the irreversible fouling were significantly controlled,evidencing that these embedment of nanoparticles had higher hydrophilicity and filterability.After employment of these modified UF membrane into an aerbic membrane bioreactor to treat real sewage,it was found that the rate of transmembrane pressure?TMP?increase was rather slow that un-modifed PVDF membrane.Meanwhile,the MBR using modifies PVDF membrane could remove up to 95% COD and 96% NH₄⁺-N.The antibiofouling tests also revealed that the microbial abundance and and population diversity on the modified membrane surface were lower than those on PVDF membrane,indicating that the embedded nanoparticles exhibited anti-adhersion ability.