Ion-Expulsion Ultrafiltration to Remove Chromate from Wastewater

In ion-expulsion ultrafiltration, a water-soluble colloid with the same charge as the target ion to be removed is added to water. This stream is then treated by ultrafiltration with membrane pores small enough to reject the colloid. In this study, chromate was removed from water using polystyrene sulfonate as the colloid in both batch-stirred cell and spiral-wound ultrafiltration devices. At very low pressures, Donnan equilibrium could be used to describe the permeate chromate concentration. As the pressure increased, diffusional effects caused the separation to become poorer. A spiral-wound unit resulted in a much higher separation efficiency than a stirred cell in this process.