Influence of concentrative and dilutive internal concentration polarization on flux behavior in forward osmosis

Osmosis through asymmetric membranes has been studied as a means of desalination via forward osmosis and power generation through a process known as pressure retarded osmosis. The primary obstacle to using asymmetric membranes for osmotic processes is the presence of internal concentration polarization, which significantly reduces the available osmotic driving force. This study explores the impact of both concentrative and dilutive internal concentration polarization on permeate water flux through a commercially available forward osmosis membrane. The coupling of internal and external concentration polarization is also investigated. A flux model that accounts for the presence of both internal and external concentration polarization for the two possible membrane orientations involving the feed and draw solutions is presented. The model is verified by data obtained from laboratory-scale experiments under well controlled conditions in both membrane orientations. Furthermore, the model is used to predict flux performance after hypothetical improvements to the membrane or changes in system conditions.