Application Of Fe₃O₄ Coated With Chitosan （Fe₃O₄/CS） To Alleviate The Fouling Rate Of MBR Membrane

Compared with the traditional activated sludge process,membrane bioreactor（MBR）has gradually become an innovative and promising technology for wastewater treatment.MBR has a great deal of advantages,such as high quality of effluent,small occupation of land,less discharge of surplus sludge,and so on.However,membrane fouling greatly increases the energy consumption and operating costs of MBR process,which restricts its industrial application.Previous studies revealed that chemical agents such as flocculants improved the properties of activated sludge mixed liquor,which alleviate membrane fouling rate.However,adding flocculants has negative effects that may change the composition of the effluent and affecting microbial activity.In addition,in order to obtain stable effect of water treatment,a large number of flocculants should be added continuously,which increased the cost of operation.In recent years,magnetic powder,a new type of coagulant aid,has been widely used to reduce membrane fouling.The present study suggested that adding magnetic powder could enhance the utilization of SMP and EPS by microorganisms,thus reducing the concentration of SMP and EPS.Moreover,granular sludge was found in the reactor added with magnetic powder and flocculant,which effectively alleviated membrane fouling.However,the mechanism of magnetic powder to alleviate membrane fouling is unclear and needs to be further studied.In this study,Fe₃O₄ coated with chitosan（Fe₃O₄/CS）was prepared to enhance the effect of magnetic powder on controlling membrane fouling.The rich amino groups of chitosan improve the surface characteristics of Fe₃O₄,which enhance its adsorption capacity to microorganisms and promote sludge granulation.The prepared Fe₃O₄/CS were characterized by transmission electron microscopy（TEM）,X ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,Zeta potential analysis,and N2 adsorption desorption technique.The results showed that Fe₃O₄/CS with high specific surface area and high density charge were prepared by hydrothermal synthesis method.In the continuous test,the optimal dosage of Fe₃O₄/CS was 80 mg/L.At this time,the membrane bioreactor’s sustainable filtration time reached 13 d,which was 2.16 times as much as that of the control group,which significantly slow down the membrane fouling.The activity of dehydrogenase was increased by Fe₃O₄/CS,and the dehydrogenase activity increased to 117.5mg/L at the optimal dosage,while the control group stabilized at 67.8mg/L,which reduced the concentration of SMPp and EPSp in the liquid.At the same time,a large number of surface amino of Fe₃O₄/CS can effectively reduce the Zeta potential of mixture,which was believed to facilite the aggregation of activated sludge flocs,Magnetic granular sludges with core of Fe₃O₄/CS were formed in reactor,which further strengthen the magnetic powder to slow down the membrane fouling.Furthermore,the characteristics of mud cake on the surface of the membrane were investigated by Fourier-transform infrared spectroscopy,scanning microscopy,energy dispersive spectrometer and so on,and the mechanism of Fe₃O₄/CS to mitigate membrane fouling was further analyzed.