Energy Recovery in Membrane Capacitive Deionization

TLDR

MCDI is a water desalination technology that applies a cell voltage between porous carbon electrodes, with ion‑exchange membranes and a spacer guiding the water flow. The study demonstrates that up to 83 % of the energy used to charge the electrodes during MCDI can be recovered during regeneration. Energy recovery is achieved by controlled constant‑current charging and discharging of the electrodes. With energy recovery integrated, MCDI consumes as little as 0.26 kWh m⁻³ to lower salinity by 10 mM, outperforming reverse osmosis, yet measured consumption still exceeds thermodynamic minima, highlighting the need for further efficiency gains.

Abstract

Membrane capacitive deionization (MCDI) is a water desalination technology based on applying a cell voltage between two oppositely placed porous carbon electrodes. In front of each electrode, an ion-exchange membrane is positioned, and between them, a spacer is situated, which transports the water to be desalinated. In this work, we demonstrate for the first time that up to 83% of the energy used for charging the electrodes during desalination can be recovered in the regeneration step. This can be achieved by charging and discharging the electrodes in a controlled manner by using constant current conditions. By implementing energy recovery as an integral part of the MCDI operation, the overall energy consumption can be as low as 0.26 (kW·h)/m3 of produced water to reduce the salinity by 10 mM, which means that MCDI is more energy efficient for treatment of brackish water than reverse osmosis. Nevertheless, the measured energy consumption is much higher than the thermodynamically calculated values for desalinating the water, and therefore, a further improvement in thermodynamic efficiency will be needed in the future.