Colloidal fouling of salt rejecting nanofiltration membranes: Transient electrokinetic model and experimental study.

摘要

Membrane separation processes are widely used for separation of colloids, macromolecules, organic matter and ions. Among different membrane processes, nanofiltration (NF) is being increasingly used for removing multiple molecular weight and size solutes ranging from colloidal particles to salt using a single membrane barrier. Fouling is a commonly encountered phenomenon in membrane processes, adversely in uencing the permeate flux and membrane life. However, models of membrane fouling by multiple rejected components in the feed are mostly empirical. In this work, a transient electrokinetic model has been developed to predict the performance of salt rejecting 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 permeate flux and observed salt rejection. The study provides fundamental insight into the development of streaming potential and electroosmotic back ow 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 ow NF was conducted with silica particles and sodium chloride in aqueous systems 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.;Keywords: Membrane Filtration, Nanofiltration, Cake Enhanced Concentration Polarization, Film Theory, Kuwabara Cell Model, Levine-Neale Electrophoretic Mobility, Electroosmotic Back Flow.