Layer-by-layer Self-assembly Preparation Of PVDF/TiO₂ Modified Membrane And Its Application In Membrane Bioreactor For Wastewater Treatment

Membrane bioreactor?MBR?is a new high-efficiency wastewater treatment technology of combining the biological treatment process with membrane separation technology.MBR has been gradually popularized and used for treating municipal/domestic and industrial wastewater due to its excellent effluent quality,low sludge yield,compact device structure and small footprint.The membrane fouling is a major bottleneck of MBRs which restricts MBRs application in wastewater treatment.For membrane fouling control,surface modification of membrane materials has become one of the research hotspots in MBR systems.The Polyvinylidene fluoride?PVDF?/TiO₂ modified membrane with different TiO₂deposition layers were fabricated via electrostatic dip-coating layer-by-layer?Lb L?assembly.PVDF/TiO₂ modified membrane performances were characterized by scanning electron microscopy,Fourier transform infrared,Xray diffraction,energy dispersive spectrometer and atomic force microscope.Photocatalytic and anti-fouling properties of PVDF/TiO₂ modified membranes were investigated.The result showed that?TiO₂/PSS?₇modified membranes exhibited excellent photocatalytic activity and anti-fouling performance.The flux and anti-fouling properties of PVDF/TiO₂ modified membranes were higher than those of PVDF membrane,which indicated that the deposition of TiO₂nanoparticles on the membrane surface could improve the hydrophilicity and endow the membrane with photocatalytic activity.Synergistic effect of TiO₂photocatalysis and membrane separation enhanced the removal efficiency of foulants and reduced the trans-membrane pressure in membrane reactor.The Lanasol Blue 3R?LB?and bovine serum albumin?BSA?degradation experiments demonstrated that the PVDF/TiO₂modified membrane had a self-cleaning ability,which was assisted by photocatalysis.The antifouling performance of the PVDF/TiO₂ modified membrane was obviously enhanced,which was attributed to the decrease in adsorption interaction between PVDF/TiO₂modified membrane and bovine serum albumin during the initial adhesion phase as evidenced by the thermodynamic analysis of the interaction between the modified membrane and foulants by the extended Derjaguin–Landau–Verwey–Overbeek?x DLVO?theory.A novel moving bed-UV-photocatalytic-modified membrane bioreactor?MB-UVPMBR?was proposed to investigate wastewater treatment and membrane fouling behavior.The results showed that the effluent quality and anti-pollution performance of MB-UVPMBR system were better than that of moving bed membrane bioreactor?MBMBR?system.Under the same operating condition,the cleaning cycle of PVDF/TiO₂modified membrane was 43 days,which was 2.5 times longer than that of the original membrane.Compared with the original membrane,the cake layer resistance decreased 83%and the membrane pore plugging resistance decreased 88%of PVDF/TiO₂ modified membrane in the MB-UVPMBR system,which significantly alleviated the total membrane filtration resistance.The hydrophilicity of the modified membrane helped mitigate foulant deposition and cake layer formation on the membrane surface.The modified membrane effectively reduced the contents of soluble microbial products and foulants deposited on the membrane surface by photocatalysis.Additionally,the PVDF/TiO₂ modified membrane still has a high flux recovery rate after 5 times of fouling-self-cleaning cycle,indicating that the PVDF/TiO₂ modified membrane has a certain self-cleaning property.MB-UVPMBR system showed a high removal effect on organic matter,and the removal efficiency of LB reached 85.1%significantly higher than that of MBMBR system.A part of LB was degraded by PVDF/TiO₂ modified membrane under UV irradiation,thus improving the dye removal efficiency of the system.By analyzing the membrane resistance distribution of the two systems,it was found that the main formation of membrane fouling was mainly accribed to the deposition of cake layer on membrane surfaces.The total filtration resistance of the membrane in the MB-UVPMBR decreased by 67.5%compared with MBMBR due to the hydrophilicity and photocatalysis of the PVDF/TiO₂ modified membrane.Overall,the removal efficiency of organic pollutants by MB-UVPMBR system was better than that of MBMBR system.