Impact of Improvements in Energy Efficiency in Capacitive Deionization Systems
Overall, CDI systems are considered to be more efficient than RO membranes for many lower concentration salt streams (<5000 ppm) due to differences in its separation mechanism.4 Shown in Figure 1 is an energy cost comparison of CDI and RO technologies as a function of salt concentration. CDI is shown with energy recovery values of 0, 25, and 50%. As the concentration of NaCl decreases, there is a distinct region where the energy cost of this separation can best RO.
The more recent addition of ion-exchange membranes in a membrane capacitive deionization (MCDI) process can further increase the charge efficiency to over 100% in certain instances and aid in further decreasing energy costs.5 The efficiency of both the CDI and MCDI process make them attractive options for many larger scale applications where energy cost becomes a dominant factor in choosing the water treatment system. In this talk, a comparison between the energy costs of RO and CDI/MCDI will be given. The use of recent surface chemistries to increase the charge efficiency will be shown to decrease the energy cost of CDI/MCDI processes further. Finally, applications will be reviewed where CDI and MCDI can be used as a standalone option as well as interface with existing membrane processes.
The authors are grateful to the U.S. - China Clean Energy Research Center, U.S. Department of Energy for project funding (No. DE-PI0000017).
1. S. Porada, R. Zhao, A. van der Wal, V. Presser and P. M. Biesheuvel, Progress in Materials Science, 58, 1388 (2013).
2. E. Avraham, M. Noked, I. Cohen, A. Soffer and D. Aurbach, Journal of The Electrochemical Society, 158, P168 (2011).
3. X. Gao, A. Omosebi, J. Landon and K. Liu, Journal of The Electrochemical Society, 161, E159 (2014).
4. Y. Oren, Desalination, 228, 10 (2008).