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Durham University

Department of Engineering

Staff Profile

Publication details for Professor Jun Jie Wu

Wu, Jun Jie (2019). On the application of the Spiegler-Kedem model to forward osmosis. BMC Chemical Engineering 1: 15.

Author(s) from Durham

Abstract

In Forward Osmosis the diffusion of the solute is counter to that of the solvent i.e. there is so-called “reverse salt
diffusion”. Furthermore, the ratio of the two fluxes is generally taken to be a constant because of the assumption of
ideal semi-permeability. However with the Spiegler-Kedem (S-K) model there is an allowance for a minor deviation
from ideal semi-permeability and the ratio of the solute flux and solvent flux is no longer constant. The theoretical
variation of the solute flux with increasing draw solution concentration is illustrated for various degrees of deviation
from ideal semi-permeability. A novel variant of the S-K model is also introduced and predictions compared with
those obtained using the standard form. With the acceptance that the form of “breakthrough” involving co-current
flow is impossible, a limitation is imposed upon the S-K model but even with this limitation the theoretically
predicted variation of solvent flux with increasing draw concentration is for certain sets of parameters of an
unexpected form for minor deviation from ideal semi-permeability. That intriguing counter-intuitive outcomes can
result from application of the S-K model indicates a need to rethink its formulation of the equations and the
expressions for the coefficients. This will have implications for forward osmosis and possibly reverse osmosis modelling.