Three-dimensional Analysis Of The Spatial Distribution Of Contaminants In Hollow Fiber Membrane Filtration And Backwashing

Ultrafiltration(UF)membrane system is an attractive option in drinking water production and waste water treatment due to its ability to provide high effluent quality and minimize plant footprint.However,membrane fouling remains a major obstacle to wide application.In the present work,Bovine albumin serum(BSA)and sodium alginate(SA)were chosen as a model foulant,and the fouling behaviors of the membranes at different operating conditions were characterized by fluorescence labeling and confocal laser scanning microscopy(CLSM).Qualitative and quantitative analysis of foulant in and on membranes were given by Image J software,exploring the mechanism of membrane fouling.Firstly,during the filtration process of using a single pollutant(BSA),the fouling behaviors of the membranes with different filtration time were investigated and the results showed that pollutants were accumulated in the junction of finger pores and sponge structure,after reaching saturation,the pollutants migrated internal with the extension of the running time.Finally,BSA evenly distributed inside the membrane and formed cake layer on the membrane surface.The influence of different flux on membrane fouling were investigated and the results showed that under the certain flux condition,the internal adsorption reaching saturation and the accumulation of BSA on the membrane surface formed a thick cake layer at the same time.This flux is defined as critical flux,and membrane fouling is more serious at this time.The effect of membrane surface adsorption on the distribution of BSA on/in the membrane was studied and the results showed that static adsorption for a period of time could reduce the internal adsorption,which effectively slow the membrane fouling process.In addition,the effect of different washing conditions on the removal of BSA on/in the membrane and flux recovery,results showed that the way of backwashing and a certain concentration of caustic washing could enhanced remove the pollutants on/in the membrane.Secondly,the influence of BSA and HA coexistence on membrane surface fouling layer and internal adsorption were investigated and the results showed that SA formed gel layer on the membrane surface and not to enter into internal formation plugging at separate filtering SA solution,but the gel layer was difficultly removed byhydraulic cleaning.Both interactions of BSA and SA coexistence leaded to adsorption and adhesion together each other,which prevented the BSA molecules into the film pores.At the same time,the presence of BSA influenced the formation of SA reunion gel layer,due to improving the dispersion of the SA.At last,the influence of the dopamine hydrophilic modification on membrane pollutant distribution was investigated and the results showed thatthe modification of membrane surface was benefit to slow adsorption of BSA and alleviate membrane fouling.The gel layer of the membrane surface adsorption formation was larger contribution to the membrane resistance growth and belonged to reversible fouling.The irreversible fouling had little contribution to membrane resistance because membrane pore internalwall adsorbed BSA.Therefore,the existence of BSA made SA molecules into membrane pores,adsorbed in membrane or entered into the effluent,which aggravatesirreversible fouling and reduces retention rate.This paper provides a reliable scientific basis for optimizing the operating conditions and improving the cleaning process in the practical application,laying the theoretical foundation for the future development of membrane separation technology for water purification process.