Capacitive deionization for water desalination: Cost analysis, recent advances, and process optimization

Capacitive deionization (CDI) is a promising and developing electrochemical technology utilized to desalinate salt water and produce fresh water. Multiple technologies, such as reverse osmosis, humidification-dehumidification, nanofiltration, and multi-stage flash, have been developed for water desalination and treatment. CDI significantly increases water desalination efficiency while maintaining an acceptable cost and energy consumption. Another essential advantage of the CDI is the removal of the dissolved ions in a selective manner. CDI system utilizes a pair of charged electrodes through which the feed water will pass forward; the charged ions in the feed water are extracted by applying an electrical voltage across the electrode pairs, and the charged ions tend to drift to the oppositely charged electrodes. This paper critically reviews the state of the art of CDI technology and its development since its invention in the mid-1960. Moreover, membrane capacitive deionization (MCDI) and flow electrode capacitive deionization (FCDI) are two essential types of CDI technology, which are discussed in detail. The CDI electrodes' materials and composition, electrochemical properties, and characterization techniques are addressed. An analytical cost framework for CDI, MCDI, and FCDI according to the levelized cost of water is provided. In addition, recent advances in CDI, including hybrid CDI-desalination technologies and CDI's sustainability and environmental impact approach, are also discussed. Lastly, process optimization and the current market of CDI technology are highlighted.