Performance decline due to cake enhanced concentration polarization in cross flow membrane filtration: An transient electrokinetic model and experimental observation

摘要

Fouling of nanofiltration membranes by multiple rejected components adversely increases the operatingpressure, decreases the performance and requires cleaning. Considerable attention has beendevoted toward understanding the fouling phenomena and developing models. However, the models aremostly empirical and fail to establish mechanistic link between the different phenomena. In this context,a transient model has been developed to predict the performance decline due to colloidal fouling ofnanofiltration membranes. The model combines the transient growth of cake layer and cake enhancedconcentration polarization (CECP) phenomenon to predict the permeate ux and observed rejectiondecline during cross flow membranefiltration. The cake layer has been considered as a swarm of noninteracting,incompressible, spherical, charged particles and represented using the Kuwabara cell model.The model also provides fundamental insight to the development of streaming potential and electroosmoticback flow, due to transport of ions around the charged colloidal particles of the cake layer, in lightof classical Levine-Neale model of electrophoresis in concentrated dispersions. The CECP phenomenahas been accounted by considering the hindered back diffusion of ions through the tortuous path of thecake layer. These phenomena are then combined with the film theory of cross ow filtration for predicatingthe permeate ux and observed rejection. In order to validate the developed model fouling ofnanofiltration membrane by colloidal silica particles were carried out and the results were compared withthe model predictions. Statistical analysis reveals the model is in good agreement with experimentalresults with only one adjustable parameter, cake porosity.