In this work, transport of mono and divalent ions through nanofiltration membranes using Donnan-steric pore model and dielectric exclusion (DSPM-DE) has been simulated. Dielectric effects were based on Born and image force effects. Donnan equilibrium was used for electrical effects. The model predicts rejection of ions, Donnan potential, and interaction energy due to image forces in the nanofiltration process. The model findings predict the rejection of symmetric monovalent ions as a function of the membrane charge density. It is indicated that a significant decrease in the interactions among the ions and their images causes the Donnan exclusion to be predominant at higher membrane charge densities. Consequently, higher membrane rejections are obtained. The findings of the developed model are valuable in predicting the nanofiltration behavior at various operating conditions as well as different membrane characteristics. (C) 2011 Elsevier B.V. All rights reserved.