Colloidal Fouling of Salt Rejecting Nanofiltration Membranes: Transient Electrokinetic Model and Experimental Study

Abstract

Membrane separation processes are widely used for separation of colloids, macromolecules, organic and ions. Among different processes, nanofiltration (NF) is being increasingly used for removing multiple molecular weight and size solutes using a single membrane. Fouling is a commonly encountered phenomena in membrane processes, adversely influencing the permeate flux and membrane life. In this work, a transient electrokinetic model has been developed to predict the performance of salt rejecting NF membranes in presence of colloidal particles. The model combines the transient growth of colloidal cake layer and cake enhanced concentration polarization (CECP) of the salt to predict the performance. The study provides fundamental insight into the development of streaming potential and electroosmotic back flow due to transport of ions around the charged spherical particles of the cake layer based on the Levine-Neale cell model of electrophoresis. This model is then coupled with film theory to assess the permeate flux decline and salt rejection during NF. To validate the model with experimental results, cross flow NF was conducted with silica particles and sodium chloride solution over a range of operating conditions. The model predictions of flux and cake layer fouling were found to be in good agreement with the experimental results.