Study on solute transport through RO/NF membranes

Abstract

The overall purpose of this research was to investigate the mechanisms and behaviors of the solute transport through RO/NF membranes. In this work, the Nernst-Planck-Donnan model incorporated with Freundlich isotherm has been developed for loose membranes. Electrostatic interactions on ion transport through RO/NF membranes have been oversimplified by electroneutrality assumption in NPD model, but it can be well described with the newly developed unsteady-state model by using Nernst-Planck-Poisson equations with dynamic boundary conditions. Transport mechanisms have also been investigated in terms of diffusion, electromigration and convection. Simulation results show that an electric field is noted to be induced by the imbalanced charges across the membrane. The transports of different ions are coupled and regulated by electro-migration within the membrane. Moreover, in multi-electrolyte solutions the addition of a third ion can increase the permeability of more permeable ion and increase the rejection of less permeable ion.