In-situ Advanced Oxidation Processes In External Membrane Bioreactors For Fouling Control

Microbial quorum sensing(QS)induces biofilm formation on the membrane surfaces and leads to severe biofouling,which remains a major bottleneck for the widespread application of membrane-based technology.Two in-situ advanced i.e.,photocatalysis and UV/O3,were studied for membrane fouling control and advanced wastewater treatment in external membrane bioreactors.The experiment was divided into two phases.Phase I(photocatalytic phase),Ti O2 nanoparticles immobilized in polysulfone-alginate polymer as the porous photocatalysts beads were used in an integrated upflow anaerobic sludge blanket – photocatalytic membrane reactor(UASBPMR)system and a ceramic membrane reactor(CMR),and the fouling control performance was examined under different UV light conditions with synthetic wastewater and real textile wastewater,separately.Phase II(UV/O3 phase),a ceramic membrane reactor(CMR)combined with a UASB reactor was used to treat real textile wastewater,and the membrane fouling control efficiencies of in-situ UV and(or)O3were examined the transformation mechanism of dissolved organic matter(DOM)in textile wastewater was also explored.The results are as follows:1.The UASB-PMR system showed a 7-folds higher efficacy in membrane fouling control than the UV photolytic QQ system(19.1±2.4 d vs.2.7±1.0 d),where vacant polymeric beads without Ti O2 were used,under intermittent UV irradiation(17 % of total operation time).Confocal laser scanning microscopy(CLSM)and scanning electron microscopy(SEM)images confirmed mitigation of biofouling in photocatalysis.2.The reactive oxygen species(ROS)generated by the UV-excited Ti O2 not only oxidized the foulants on the membrane surface,but also quenched N-acyl-homoserine lactones(AHLs),the QS signal molecules,thus reduing biofilm formation.Additionally,almost complete disinfection of the effluent was realized in the photocatalytic system.Therefore,photocatalytic system retard membrane fouling to the maximum extent.3.In-situ ozone treatment in CMR showed high potential in color removal but resulted in an increase in the membrane fouling rate with the increasing ozone dose;the continuous UV(254 nm)exposure significantly retarded membrane fouling by 16 folds,but increased soluble chemical oxygen demand.In contrast,when intermittent(15 min ON: 15 min OFF)UV exposure and ozonation(UV/O3)were applied simultaneously,94 % color removal was reached and a synergistic effect on membrane fouling control was prominent,which reduced the fouling rate by 2.95 and 10.13 folds as compared to the standalone application of UV or ozone,respectively.4.CLSM observation revealed proteins and polysaccharides as the prominent foulants in O3 and UV treatment,respectively.UV-Vis spectroscopy and 3-D excitation emission matrix fluorescence spectra(EEM)confirmed the wastewater advanced treatment synergitic effects of UV/O3 in degradation of UV280 and UV254 absorbance and fluorescent DOM.This study provides a new approach for the treatment of textile or other industrial wastewater by external membrane bioreactor(MBR)with in-situ photocatalysis or UV/O3 as the fouling control measure,which not only has a high efficiency of fouling control,but also partially mineralizes the organic pollutants in the effluent.