An electrokinetic model for combined fouling during cross flow filtration of electrolyte solution and charged Colloids

摘要

Colloidal fouling, formation of a cake due to deposition of colloids on to a membrane, is commonlyencountered in pressure driven filtration processes, such as nanofiltration and reverse osmosis.The influence of these deposited charged colloids on the ion concentration polarization,ion rejection and the overall permeate flux is the focus of the present work. A common situationencountered during membrane filtration is the combined influence of charged colloids and the associatedelectrolyte on the flux decline and rejection. In this context, coupled model of concentrationpolarization (CP), cake layer formation by charged colloidal particles and ion transport through theinterstitial spaces of the cake layer has been developed to predict the permeate flux decline andobserved salt rejection during cross flow filtration of an electrolyte and colloidal mixture. The suspensionstructure of the cake layer is considered as a swarm of colloidal particles, represented usingthe Kuwabara cell model. For this system, the electroosmotic flow is calculated analytically usingthe Levine-Neale model. The analysis is then combined with the standard film theory of cross flowmembrane filtration to predict the flux decline, observed rejection, cake layer thickness and resistance,and osmotic pressure difference. The model illustrates the combined influence of electricaland physical properties of colloids and electrolytes, mass transfer coefficient or crossflow conditionand membrane resistance on the separation process. This approach provides a comprehensiveinsight into the mechanism of cake enhanced concentration polarization for charged colloids.