A new open access paper was recently published in Desalination that compares the energy use of RO and CDI.
Porada et al. “Energy consumption in membrane capacitive deionization and comparison with reverse osmosis”, Desalination (2020), https://doi.org/10.1016/j.desal.2020.114383.
According to the authors, "the work presents the first fair energy consumption comparison of desalination with MCDI and RO. The comparison is based on experimental data, and the data is compared with results from state-of-the-art theoretical models. We find that the energy consumption difference between RO and CDI is much less than recently reported by the group of Prof. Elimelech (Yale, USA), see weblink."
The authors emphasize that two technologies can only be compared when all metrics are used in the same uniform way, and when for each technology state-of-the-art is considered. A new operational mode for CDI is introduced with a long "hold time" during salt release, leading to unprecedented high values of water recovery obtained in CDI with high feed water salinity of 40 mM NaCl solution.