Simulation of an energy self-sufficient electrodialysis desalination stack for salt removal efficiency and fresh water recovery

Abstract

Electrodialysis is a commonly used desalination method. In this study, we investigate its hybridization with its reverse process, where reverse electrodialysis (RED) harvests the salinity gradient power to provide the driving force for electrodialysis. In particular, the desalination performance (rejection and recovery) and their tradeoff relationship are simulated for the first time for an energy self-sufficient RED-ED desalination stack (REDD). The simulation results show that these two parameters can be simultaneously optimized by tailoring ion exchange membranes in the stack, i.e., using more selective membranes in the ED sub-cell (EDcell) and less selective membranes in the RED sub-cell (REDcell). Our analysis shows that a considerable driving force (e.g., a salinity ratio of high salinity stream to low salinity stream over 30 and a volumetric ratio over 0.5) is required to fully unleash the desalination performance of REDD, leading to a favorable shift of the rejection-recovery tradeoff line. In addition, multi-pass treatment is demonstrated to further enhance rejection at the expense of lower recovery. Similarly, a multi-stage configuration can be applied for higher recovery. This study reveals the operational constraints of a novel desalination REDD technique and provides insights into performance enhancement.