Development of an integrated capacitive-electrodialysis process (CapED) for continuous, low-energy electrochemical deionization

Abstract

A membrane stack configuration with activated carbon electrodes was developed to integrate the capacitive and electrodialysis contributions for continuous, low energy desalination. • A cell was developed by stacking IEMs between capacitive electrodes. • During the charging step, the ions were removed by electrosorption/electrodialysis. • During the discharging step, the ions were removed by dialytic separation. • The continuous desalination was achieved by a cyclic charging/discharging process. • High charge efficiency and low energy consumption were achieved. Significant efforts have been made to develop advanced energy-efficient desalination technologies for delivering freshwater. Capacitive deionization and electrodialysis represent electric field-driven separation technologies for water desalination. In this study, a new design for a membrane stack configuration based on an integrated capacitive-electrodialysis process (CapED) was proposed for continuous and energy-efficient desalination. From the activated carbon anode to the cathode, an anion exchange membrane (AEM), a cation exchange membrane (CEM), an AEM, and a CEM were placed in order (anode/AEM/CEM/AEM/CEM/cathode). Herein, three chambers between two capacitive electrodes were separated by a CEM and an AEM, which enabled simultaneous and continuous generation of desalinated and concentrated solutions. During charging, capacitive electrosorption and electrodialytic separation accounted for desalination. During discharging, the energy stored by capacitive electrosorption was utilized for desalination through dialytic separation. Therefore, continuous desalination could be achieved by a cyclic charging/discharging process. In addition, the salt removal amount was enhanced by increasing the voltage with respect to the different capacitive and electrodialytic contributions. The energy consumption ranged between 0.53 and 1.45 kWh/kg with high charge efficiency, indicating a low energy requirement. Our research showed that CapED was effective when integrating capacitive and electrodialytic contributions for electrochemical water desalination.