| In recent years,Membrane bioreactors (MBRs) as a versatile technique have been widely used in wastewater treatment and water reuse.However, membrane fouling is a major obstacle to the wide application of MBRs, which leads to shorter membrane life, more frequent chemical cleaning, reduced membrane flux and higher operational costs.Thus, developing low cost and antifouling membrane material is the highlight of study. It is essential for the application of membrane steadily and development of MBR. In this work, a novel membrane material, which was fabricated by modification the non-woven fabric (NWF) with hydrophilic poly(N-Vinyl-2-pyrrolidone) (PNVP) using the Atom Transfer Radical Polymerization (ATRP) method, was developed according to the fouling characteristics in MBR. The preparation conditions, characterization and antifouling property of modified membranes were investigated. Results are shown as follows:(1)A hydrophilic polymer, poly(N-Vinyl-2-pyrrolidone) (PNVP), was grafted on the surface of Polypropylene non-woven fabrics (NWF) membrane via ozone surface activation and ATRP to improve the hydrophilicity and antifouling property. Effects of grafting time, grafting temperature and monomer concentration on the grafting degree of PNVP were systematically investigated, which results demonstrated the controlled fashion of ATRP.(2) The FTIR spectrum indicated that PNVP was successfully immobilized on the surface of NWF membrane; SEM pictures demonstrated that the membrane was covered by a thick polymer layer and had a smaller pore size. The results of measured water dynamic contact angles indicated that the hydrophilicity of the modified membrane was enhanced with the grafting time increasing, and water dynamic contact angles decreased from 113.0±1.2°for the original NWF to 52.1±3.0°.The surface free energy measured by water angle and octane angle increased with an increased grafting time, and the polar groups of PNVP on the membrane surfaces played a crucial role in the increase of the total surface free energy.(3)Static BSA adsorption tests were conducted to evaluate the NWF fouling potential caused by NWF surface-protein interaction. The average amount of BSA adsorption for the original NWF membrane was 122.47 mg/m2, while the least value for the PNVP-modified was 21.5 mg/m2 and decreased by 82.5%,indicating that protein adsorption of NWF can be improved obviously by the immobilization of PNVP. (4) The permeation experiments were carried out to measure the antifouling property of the modified membranes.The results showed that the modified membranes had higher permeation fluxes with enhanced rejection rates, improved flux recovery, lower flux loss. When filtrating the supernatant solution of activated sludge, modified membranes had an enhancing tendency toward antifouling property with increasing the grafting time, which was shown by the decrease of relative flux reduction (RFR),from 92% for the nascent NWF membrane to 74% for the modified membrane with 6 h grafting time.(5) The bacterial adhesion on the membrane surface was also conducted to evaluate the anti-bacterial adhesion activity, which results showed that the amount of bacteria adhered on the original NWF membrane surface increased as the ionic strength of bacteria solution increased;however,the amount of adhered bacteria on PNVP-modified membrane surface decreased sharply and was independent of ionic strength, the bacteria reversibly attached on the membrane surface can be mostly washed away by physical cleaning, indicating the reversible adhesion. This conclusion will largely improve the application of NWF in MBRs.
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