Capacitive deionization for wastewater treatment: Opportunities and challenges

Capacitive deionization (CDI) is an emerging method for removal of charged ionic species from aqueous solutions, based on electrostatic interactions between (mostly) inorganic ions and porous carbon electrodes. Inspection of recent publications related to CDI processes, revealed that the majority of the publications are related to the removal of salt (NaCl) from the water (desalination) or electrosorption processes. However, such a water desalination is only one process in the improvement of the quality water, it is interesting to review the literature in the context of CDI processes for other water treatment processes. Herein wastewater treatments are discussed. In this paper, we critically review the last publications that relate to capacitive deionization with wastewater treatments. Since wastewater treatments may involve broad aspects, we address in this review four specific water treatment processes that are thought to be connected with CDI processes: organic fouling of CDI cells, removal of heavy metals by CDI processes, removal of organic micropollutants with CDI processes and disinfection with CDI processes. We also evaluate herein the status of several research efforts in this area and suggest future directions.