Mitigation Of Membrane Fouling Through Adding Flocculant And Magnetic Powder In Membrane Bioreactor

Membrane bioreactor(MBR)is considered as an efficient way to remove physical,microbiological as well as chemical contaminants from the treated water.While membrane fouling remains the bottleneck for its widespread application,MBR operation with flocculant addition can effectively mitigate the membrane fouling in MBR.Membrane fouling alleviation by addition of poly dimethyl diallyl ammonium chloride(PDMDAAC)and magnetic powder(Fe3O4)was investigated in this study.It was found that PDMDAAC associated with magnetic powder had a good performance on mitigation of membrane fouling,improvement in dehydrogenase activity and enhancement of biomass growth.The optimal dose of PDMDAAC was determined by using constant pressure dead-end filtration unit.Maximum permeate flux was attained at 400 mg/L of PDMDAAC addition.Continuous experiment was conducted in a submerged membrane bioreactor(MBR)system and biomass parameters such as soluble microbial products(SMP: mainly contains protein(SMPp)and carbohydrate(SMPc)),extracellular polymeric substances(EPS: mainly contains protein(EPSp)and carbohydrate(EPSc)),dehydrogenase activity,zeta potential,and capillary suction time(CST)were analyzed.The results indicated that addition of 400 mg/L of PDMDAAC revealed a minor impact on microbial activity and the effluent COD,and also PDMDAAC had better performance in SMPc and EPSc reduction.While the addition of magnetic powder could effectively improve dehydrogenase activity especially at the suitable temperature.Dehydrogenase activity reached to 97.1 mg/L at the optimal dose of 120 mg/L of magnetic powder.whereas magnetic powder played a major role in decreasing SMPc and EPSp,resulting in mitigation of membrane fouling.In comparison with the MBRs supplemented PDMDAAC alone,widowed caterpillars and numbers of vorticellae as well as larger flocs were observed in the MBRs with addition of PDMDAAC and magnetic powder from the microscope.And sustainable filtration time of 20 d was obtained with a combination of 120 mg/L of magnetic powder and 400 mg/L of PDMDAAC.