Fabrication Of Nanomaterial Modified Ultrafiltration And Nanofiltration Membranes Based On The In-situ Embedment Approach

Membrane fouling is a big problem during the application of ultrafiltration and nanofiltration membranes in water and wastewater treatment. Nanomaterials were used to modify ultrafiltration and nanofiltration membranes in order to enhance the antifouling abilities. Nanomaterial embedded ultrafiltration membranes were prepared using the in-situ embedment method, which were then used as the support membrane for nanomaterial modified nanofiltration membrane fabrication via interfacial polymerization. The properties of the unmodified and modified membranes were evaluated by conducting contact angle measurement, filtration test, bacteria adhesion test, bacterium inactivation test, biofilm formation test and rejection test for trace organic substances.Among the several aluminum and/or silicon oxide nanoparticles tested, alumina(Al2O3) and Linde type L(LTL) zeolite nanoparticles(500 mg/L in water bath) were stably embedded which could be evenly dispersed on membrane surface with high coverage ratio(37.7% and 48.9%, respectively). The in situ embedment of nanoparticles did not alter the cross section and bottom morphologies of the ultrafiltration membranes, but increased the surface roughness. The contact angles of the nanoparticle embedded ultrafiltration membranes(UF-Al2O3 and UF-LTL) were 63.2° and 49.4°, respectively, lower than that of the control ultrafiltration membrane(UF-C)(66.2°), and the membrane resistance of UF-Al2O3 and UF-LTL were 70.0% and 72.3% of that for UF-C. Though UF-Al2O3 and UF-LTL had no bacteriocidal effect on E. coli, they exhibited a high anti-adhesion efficiency to both E. coli and P. aeruginosa. The anti-biofouling ability of UF-Al2O3 and UF-LTL mainly benefited from the anti-adhesion ability attributed to the embedded nanoparticles.Nanomaterial modified nanofiltration membranes(NF-LTL) were prepared by interifacial polymerization of piperazine in the aqueous phase and trimesoyl chloride in the organic phase using UF-LTL as a support layer. Nanoparticles had a good dispersion in the polyamide thin film layer with a relative high coverage without NaOH in the aqueous phase. LTL nanoparticles had no impact on membrane hydrophilicity, but could effectively reduce membrane resistance. The membrane resistance of NF-LTL was half of that for the control nanofiltration membrane(NF-C). NF-LTL exhibited a 93.4% rejection rate to MgSO4 and a 27.7% rejection rate to NaCl, showing a slight decrease as compared to NF-C. The channels that LTL had through which water molecules could pass and some defects occurred during the formation of the thin film layer as the embedment of nanoparticles might be responsible for the decrease of membrane resistance and salt rejection rates. In addition, the LTL nanoparitlces in the polyamide thin film layer had no influence on the rejection rates for trace organic substances. As nanoparticles were buried in the thin film layer, NF-LTL showed no anti-biofouling abilities.