A spacer element (1) is disclosed having an integral screen for use in filled cell electrodialysis. The spacer (1) has a continuous portion (2) impermeable to flow and a screen (3) which spans a centrally-located flow treatment region that contains active treatment material, such as ion exchange beads. The screen (3) may perform a structural function, allowing operation at elevated pressure, and may also define a minimum gap between adjacent membranes and enhance mixing along the flow path and at cell boundaries. The spacer element (1) may be configured to enhance hydraulic filling of the cells, and cell architecture is readily implemented in a wide range of useful flow path geometries utilizing the screen spacer element (1).