Mechanism Of Membrane Fouling Control And Trace Organic Compounds Removal By Electric Field Enhanced Microfiltration

Microfiltration（MF）technology is now widely used in reclaimed water treatment processes,but membrane fouling formation and low removal of pollutants such as trace organic compounds（Tr OCs）during operation are the main challenges.In this study,the electric field was applied in the microfiltration system to analyze the relationship between the structural change of typical foulants and the formation of membrane fouling in the electric field,and explore the removal mechanism of electric field for Tr OCs in the treatment for the synthetic water and the secondary effluent of an sewage plant with laboratory scale,providing the theoretical basis and technical reference for the development of membrane fouling control and Tr OCs removal technology.Eight common Tr OCs in reclaimed water were chosen as target Tr OCs.A solid-phase extraction-liquid mass spectrometry detection method was developed for the determination of Tr OCs.The effects of membrane materials,inorganic ions,and p H on the removal of Tr OCs and the performance of electric field coupled MF on Tr OCs removal were investigated.It was verified that the electric field could strengthen the removal of Tr OCs from less than 40%to more than 90%during the MF process.A dynamic small-scale reactor was constructed with a hollow fiber membrane to investigate the structural changes of typical foulant proteins in an electric field.The active chlorine generated on the anode led to protein denaturation and unfolding.Under the action of electrophoretic migration,the denatured proteins aggregated into flocs with much larger particle size than the membrane pore size,and thus prevented the blockage of membrane pores.At 3 V,the formation of hydraulic irreversible membrane fouling could be reduced by 70.5%.In the electric field,electrophoretic migration could also increase the contact time of Tr OCs and oxidants,and the removal of Tr OCs was improved from 6.3%～13.8%to 34.4%～91.6%.As a typical cation in water,Ca²⁺always aggravates the membrane fouling and affects the removal of Tr OCs.Ca²⁺inhibited the effect of electric field on membrane fouling control and Tr OCs removal.At 3 V,due to the bridging interaction between Ca²⁺and carboxyl functional groups on protein molecules,denatured protein tended to form compact floc particles with small size and better settleability,which reduced the deposition of protein on the membrane surface and tended to form a thin and porous membrane fouling structure,achieving the 64.5%membrane fouling reduction and nearly 100%protein removal.In the electric field coupled coagulation and activated carbon adsorption system,the electric field changed the surface charge distribution of dissolved organic matters and inorganic particles,reduced the electrostatic repulsion between pollutants,promoted the aggregation of pollutants and the formation of flocs,which reduced the deposition of pollutants on the membrane and thus alleviated the membrane fouling.The transmembrane pressure could be reduced by 80.7%at 2.5 V.Electrochemical oxidation was the main contributor to the Tr OCs removal,which could also prolong the effective adsorption time of PAC by removing Tr OCs absorbed on PAC.The secondary effluent from a sewage treatment plant was used as feed water.The electrolysis process on the electrodes reduced the p H in the electric field and generated the active chlorine,which inhibited the adhesion of microorganisms on the membrane surface,and changed the organic components of the membrane fouling from protein and polysaccharide to humic substances and polysaccharide.The electrophoretic migration and acidic environment promoted the aggregation of humic substances and led to the formation of the hydrophilic porous membrane fouling structure.Under the applied voltage of 3 V,a 70.8%transmembrane pressure reduction and 35.9%～84.8%removal of Tr OCs could be achieved.