Progress and outlook for capacitive deionization technology

Capacitive deionization (CDI), an emerging desalination technology, has received considerable attention in recent years due to porous carbon development, new cell designs, and unique operational modes providing higher performance for capacitance-based salt removal. The energy cost of this separation process has also been rigorously evaluated through a variety of efficiency calculations, and direct comparisons are now being made with more conventional membrane-based separation systems. Currently, the thermodynamic energy efficiency (TEE) of CDI is quite low with values typically below 5%, although there are examples where this efficiency can reach 10% or higher under the proper conditions. As the development of CDI and analogous capacitive processes continue, the TEE should remain a metric for comparison to conventional techniques. In addition, the ability of CDI to perform selective separations for trace compounds, resource recovery, and contaminant removal should be more heavily investigated.