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Energy Efficiency of Electro-Driven Brackish Water Desalination: Electrodialysis Significantly Outperforms Membrane Capacitive Deionization
journal contribution
posted on 2020-03-05, 22:29 authored by Sohum
K. Patel, Mohan Qin, W. Shane Walker, Menachem ElimelechElectro-driven
technologies are viewed as a potential alternative
to the current state-of-the-art technology, reverse osmosis, for the desalination of brackish waters.
Capacitive deionization (CDI), based on the principle of electrosorption,
has been intensively researched under the premise of being energy
efficient. However, electrodialysis (ED), despite being a more mature
electro-driven technology, has yet to be extensively compared to CDI
in terms of energetic performance. In this study, we utilize Nernst–Planck
based models for continuous flow ED and constant-current membrane
capacitive deionization (MCDI) to systematically evaluate the energy
consumption of the two processes. By ensuring equivalently sized ED
and MCDI systemsin addition to using the same feed salinity,
salt removal, water recovery, and productivity across the two technologiesenergy
consumption is appropriately compared. We find that ED consumes less
energy (has higher energy efficiency) than MCDI for all investigated
conditions. Notably, our results indicate that the performance gap
between ED and MCDI is substantial for typical brackish water desalination
conditions (e.g., 3 g L–1 feed salinity, 0.5 g L–1 product water, 80% water recovery, and 15 L m–2 h–1 productivity), with the energy
efficiency of ED often exceeding 30% and being nearly an order of
magnitude greater than MCDI. We provide further insights into the
inherent limitations of each technology by comparing their respective
components of energy consumption, and explain why MCDI is unable to
attain the performance of ED, even with ideal and optimized operation.