Modeling reverse draw solute flux in forward osmosis with external concentration polarization in both sides of the draw and feed solution

Abstract

A model was developed for realizing the theoretically predicted performance of a forward osmosis (FO) system with an asymmetric membrane. The developed model has the capability to describe significant physical processes occurring in the FO system, such as reverse draw solute flux and internal (ICP) and external concentration polarization (ECP). The model was verified using existing experimental data and was used to investigate the effect of operating conditions such as cross-flow velocity and solute concentrations of both feed and draw solutions. It was found that the effects of the reverse draw solute flux and ECP were not negligible for predicting the water flux in some operating conditions, such as in a feed solution with a high solute concentration. However, previous FO modeling studies have generally assumed that their effects are insignificant. The effect of ECP increases with the solute concentration of the feed solution. The cross-flow directly affects the diffusion of the solute on the surface of the membrane and the ECP change could possibly affect ICP in the support layer. In this study, the simulation result confirmed the effect of the cross-flow on ECP, ICP, and water flux. These phenomena can simultaneously be simulated by the model developed in this study.