Capacitive Deionization: A Promising Water Treatment and Desalination Technology

Since the 1960s, the research community exploring electrochemical water treatment methods has shown considerable interest in Capacitive DeionizationCapacitive deionization (CDI). The operational model of this technology relies on the adsorption of ionic constituents onto high surface area electrodes, facilitated by the application of a low voltage across the system. This voltage initiates the generation of an electric field, propelling ions toward their respective countercharged electrode. These ions will be temporarily stored inside the electrical double layersElectrical double-layer (EDLs) of the porous electrodes, thereby resulting in water deionization. After saturation, these electrodes will subsequently desorb the solvated ions when the potential is switched off. Unlike other membrane and thermal desalination techniques like reverse osmosis (RO) and multi-stage flash distillation (MSFD), CDI technology interestingly targets the solutes instead of the solvent. This makes it a highly effective desalination technology for brackish water consuming less energy with a driving electric force of low 1.0–1.4 V potential with the possibility to control the desalination rate simply by adjusting the hydraulic retention time and electrical charge (cannot be done with other membrane or thermal-based desalination technologies). This chapter reviews capacitive deionizationCapacitive deionization as an electrochemical water desalination technology, its theoretical and technological aspects, the history of its development, its material and architectural aspect with extension to its counterparts which are membrane capacitive deionizationCapacitive deionization (MCDI) and flow electrode capacitive deionizationCapacitive deionization (FCDI), and attempts toward its optimization for scaling up and commercialization. This chapter also presents a critical review of the technology’s advantages and limitations.