The combined ion exchange-membrane filtration system, whereby an active filtration layer is formed using a slurry flow of resin beads and water, has the potential to reduce energy usage and increase the quality of purified wastewater. The hydrodynamic design of these systems is in its infancy and there is a need for numerical methods to analyze such systems. In this work, computational fluid dynamics coupled with the discrete element method (CFD-DEM) is utilized to analyse the hydrodynamics of the combined ion exchange-membrane filtration system, and the formation of the filtrating bed and the parameters affecting it are studied by varying the flow conditions. As a result, the details of the bed formation with insights on the parameters affecting these phenomena and suggestions for an improved hydrodynamic design of the combined ion exchange-membrane filtration system are presented. (C) 2019 Elsevier Ltd. All rights reserved.