Application of capacitive deionization technology in water treatment and coupling technology: a review

Due to the growing demand for water in human society, the shortage of water resources has become the bottleneck of ecological civilization construction and social and economic sustainable development. Therefore, the circulation and development of water resources are important measures to ensure water resources and water security. Capacitive deionization technology (CDI) offers numerous advantages, including high efficiency, energy savings, ease of operation, and renewability. It has been actively developed as a promising new technology. Following decades of research, the application of CDI has become increasingly widespread. Most of the existing literature reviews, however, are only related to seawater desalination. Consequently, this paper mainly emphasizes the most current research progress in various application fields of CDI in water treatment. The focus of this paper is on the application principles and progress of CDI in water treatment, introducing and analyzing potential research findings of CDI in water desalination, water softening, removal of heavy metals, purification of industrial wastewater, and removal of nutrients. The summary and comparison include CDI and other ion treatment technologies, such as reverse osmosis, electrodialysis, and membrane distillation. Secondly, the latest research progress on CDI coupling technology is discussed. Finally, some suggestions on the presentation present the progress of CDI technology and the prospects for the future.