Preparation Of Magnetic Coagulant And Its Application In Mitigating MBR Membrane Fouling

A large amount of domestic sewage is produced every day,and it must be effectively purified before it can be reused.Membrane bioreactor（MBR）is a high-efficiency wastewater treatment device.It has been widely used in wastewater treatment and reuse.However,the disadvantages of flux decline and operating cost increase caused by membrane fouling severely limit the larger application of MBR.Mitigating membrane fouling plays an important role for MBR technology.In this study,a magnetic composite coagulant was prepared and added into the MBR.Following,the influence of the magnetic composite coagulant on the sludge properties,the pollutants removal and the microbial communities were comparatively investigated.It is aimed to explore new methods and processes for mitigating membrane fouling and reveal the underlying mitigating mechanism in the MBR,which will improve and enrich the theory of mitigating membrane fouling in the MBR by magnetic activated sludge process.It may provide reference for the practical application of magnetic coagulant.In this study,magnetic nano/micro-particles and coagulant polyaluminum chloride（PAC）are compounded to prepare a magnetic polyaluminum ferric chloride（PFAC）coagulant for mitigating membrane fouling in the MBR.The magnetic particles,PAC and PFAC were characterized by physical properties,structure and morphology.Through the characterization of the coagulant,it was found that the experiment successfully chemically compounded the PAC with the magnetic particles.The composite magnetic coagulant changed the distribution of various forms of Al,and the surface of the coagulant become rougher and more porous,which were benefit to the coagulation effect.The terminal filtration experiment also proved that the addition of magnetic coagulant could significantly mitigate the membrane fouling.Subsequently,PAC and PFAC were added into the MBRs,and the performance was systematically investigated.It was found that the PFAC-MBR provide the better removals on COD and NH₄⁺-N than that of CAS-MBR,the sludge size increased from 64.35μm to 75.63μm,the dehydrogenase activity was also greatly enhanced,the proportion of macromolecular substances decreased,and the SMP and EPS in the sludge liquid also decreased by 24.16%and44.14%respectively.Macroscopically,the TMP of CAS-MBR reached 35 k Pa,while the TMP of PFAC-MBR was only 13 k Pa.The membrane fouling rate was reduced by nearly 62.8%.Together with the protein and polysaccharide in SMP and EPS were with the TMP profiles,they indicated a consistent trend.Analysis of microbial communities from the MBRs indicated that adding magnetic coagulant could increase the microbial diversity,and improve pollutants removal.In addition,it was found that the changes of the microbial communities were beneficial for mitigating membrane fouling.It is speculated that the introduction of magnetic coagulant inhibits the stability of Proteobacteria species that are easy to cause membrane fouling,and promotes the growth of species that are conducive to slowing membrane fouling.Therefore,the addition of magnetic coagulant in the MBR is a practical method to mitigate membrane fouling.