Study On The Fouling Mechanism Of Ultrafiltration Membrane Of Natural Organic Matter And Nano Silver Mixed Foulant

With the increase in the production and application of nanomaterials,nanosilver has been widely used in many fields such as biotechnology,electronics,medicine,environmental remediation,biosensors,agriculture and food industry.After discharge of AgNPs to land or aquatic environment,their conversion or interaction with natural organic matter in the environment may increase the possibility of ecotoxicity.Therefore,the release of AgNPs into natural aquatic ecosystems containing NOM must be evaluated in a specific environment,to explore more effective methods of removing nano silver in water.At present,ultrafiltration is the most promising and reliable technology for removing nanoparticles in water.However,membrane fouling in the process of membrane filtration will cause a decrease in membrane flux and an increase in filtration resistance,seriously reducing the sustainability and economic benefits of the membrane.It has become a major obstacle to the widespread application of ultrafiltration technology.The higher surface area/volume ratio of nanosilver makes nanosilver have unique physical and chemical properties,and discharge into water will cause very complicated changes with NOM and other aqueous solution conditions.This study uses XDLVO theory to understand and analyze the impact of different membrane materials and different solution conditions on the mechanism of AgNPs-HA ultrafiltration membrane fouling.It can also deeply analyze the main mechanism that the interaction energy can control the ultrafiltration membrane fouling of the AgNPs-HA mixture.In this study,the linear interaction between the interface interaction and the membrane fouling trend is explored and the applicability of the XDLVO theory to quantitatively evaluate the mechanism of the ultrafiltration membrane fouling of the AgNPs-HA mixture is provided.The experimental results provide theoretical support for selecting the optimal operating conditions in the actual operation of the membrane process to reduce membrane fouling.The results show that under low ionic strength and low solution pH,the ultrafiltration membrane fouled by AgNPs-HA mixed foulant is more serious.Compared with PES and PVDF membranes,the relative flux of hydrophobic PVDF membranes declines more.Compared with PES100,the membrane fouling of PES50 with smaller molecular weight was more serious.At low ionic strength,ultrafiltration membrane fouling is more serious,because Ag+ released by nano silver in water and Cl-generate more stable and negatively charged AgCl.This phenomenon causes the increasing of negative charge density and potential value of mixed foulants and membrane.This increases the electrostatic repulsion of the substance and hinders the accumulation of foulants.As the ionic strength increases,the more AgCI is generated,the electrostatic repulsion in initial and later stages increase,and the attractiveness of the interface in initial and later stages decrease,so membrane fouling is not serious.At the same pH,the membrane fouling caused by the AgNPs-HA mixture is lighter than the membrane fouling caused by the mixture of other nanoparticles and natural organic compounds.Because the background electrolyte is NaCl and the AgCl generated reduces the membrane fouling.The physical cleaning efficiency increases and the chemical cleaning efficiency decreases with ionic strength decreasing and pH increasing,indicating the increasing of corresponding reversible fouling resistance.At this time,the interface attraction between membrane-foulant and foulant-foulant decreases.Irreversible fouling mainly occurs in the initial stage of membrane filtration.Since membrane fouling behavior in the initial stage is mainly controlled by the interaction between the membrane and the foulants.The fouling mainly occurs in the pores of the ultrafiltration membrane.It can't be removed by simple physical cleaning and the proportion of irreversible fouling increasesAccording to XDLVO theory,AB interaction energy and LW interaction energy dominate the total interaction energy.At low ionic strength and low pH,interaction energy between the membrane-foulant and the foulant-foulant is smaller.In other words,the more attractive the interface is,the more serious the membrane fouling is The interaction energy of the three membranes is:PVDF 100<PES50<PES100,and the severity of membrane fouling trend is:PES 100<PES50<PVDF100.The interface energy of the initial stage and the later stage under different conditions is linearly fitted with the membrane fouling index,and it is found that the membrane fouling index and the interface interaction have a good negative linear correlation,so the XDLVO theory can be used to quantitatively analyze the membrane fouling of AgNPs-HA mixture.