Fabrication Of RO/NF Membranes With Anti-biofouling And Chlorine Resistance Properties

The irreversible decrease of the membrane performance caused by biofouling and chlorination is the critical problem to the development of reverse osmosis(RO)and nanofiltration(NF)membranes technology.To solve this problem,we improved the anti-adhesive property,anti-microbial property and chlorine resistance of the RO/NF membrane,without sacrificing the permselectivity of the membrane.The modified RO/NF membranes will have longer service life and energy and cost of the membrane processes will reduce.The zwitterionic polymer modification improved the water flux and anti-biofouling property of RO membrane.A commercial available aromatic polyamide RO membrane(TE)was modified by the redox initiated graft polymerization of N,N?-dimethylaminoethyl methacrylater(DMAEMA),followed by the surface quaternization reaction with 3-bromopropionic acid(3-BPA)to obtain the zwitterionic carboxybetaine methacrylate polymer(PCBMA)chains on the membrane surface.The water flux of the modified membrane increased 22.55% than that of the unmodified membrane,while the salt rejections of the membranes were nearly the same.The aqueous solution containing lysozyme and bovine serum albumin were used to analyze the anti-adhesive property of the membranes.The water fluxes of the modified membrane all decreased less than those of the unmodified TE membrane,and after the membranes were cleaned,the water flux recovery rates of the modified membrane were more than 92%,which were far higher than those of the unmodified TE membrane.Moreover,the mortality of Escherichia coli and Bacillus subtilis(1×106 cfu/ml),after contacted with the modified membrane,could reach to 99%.The zwitterionic polymer modification also improved the anti-biofouling property of NF membranes,and we also discuss the universality of this modification method.The zwitterionic PCBMA was grafted on two commercial nanofiltration(NF90 and NF270)membranes surfaces to improve the anti-adhesive and anti-microbial properties of the membranes.The Na Cl and Mg SO4 solutions were used to analyze the permselectivity of the membranes,which changed little after modification.After fouling tests,the decreases of the modified membranes water fluxes were significantly lower than those of the unmodified membranes,and after the membranes were cleaned,the water flux recovery rates of the modified membranes were about 95%.The anti-microbial property of the membranes was analyzed by contacting with Escherichia coli and bacillus subtilis,and the mortality of which could reach to 99%.The aromatic polyamide RO membrane modified by second interfacial polymerization of quaternized 2,6-diaminopyridine had improved the anti-biofouling and chlorine resistance properties without compromising salt rejection and water flux.A novel reverse osmosis membrane with high anti-biofouling and chlorine resistance properties was prepared by second interfacial polymerization of 2,6-diaminopyridine(2,6-DAP)and followed by the quaternary reaction with 3-bromopropionic(3-BPA).The modification was based on the aromatic polyamide RO membrane which prepared by interfacial polymerization of m-phenylenediamine(MPD)and trimesoyl chloride(TMC).The water flux and salt rejection of the unmodified and modified membrane were nearly the same.After the chlorination test(chlorine contents 500~2500 ppm ×1 h,p H 4.0),the water flux and salt rejection of the modified membranes all decreased less than those of the unmodified membrane,and the salt rejection of the modified membrane was still higher than 98%.Moreover,the mortality of Escherichia and Bacillus subtilis,after being contacted for 2 h with modified membrane,could reach to 99%.