Energy consumption in membrane capacitive deionization for different water recoveries and flow rates, and comparison with reverse osmosis

• New method of data analysis for (membrane) capacitive deionization is presented.
• Energy consumption and energy recovery (during discharge) of MCDI is analyzed.
• Constant current operational mode for MCDI results in a stable effluent salt concentration.
• Membrane capacitive deionization is compared with reverse osmosis.

Membrane capacitive deionization (MCDI) is a non-faradaic, capacitive technique for desalinating brackish water by adsorbing ions in charged porous electrodes. To compete with reverse osmosis, the specific energy consumption of MCDI needs to be reduced to less than 1 kWh per m3 of freshwater produced. In order to investigate the energy consumption of MCDI, we present here the energy consumption, and the fraction of energy that can be recovered during the ion desorption step of MCDI, as a function of influent concentration, water flow rate and water recovery. Furthermore, the energy consumption of MCDI based on experimental data of our lab-scale system is compared with literature data of reverse osmosis. Comparing with literature data for energy consumption in reverse osmosis, we find that for feed water with salinity lower than 60 mM, to obtain freshwater of ~ 1 g TDS/L, MCDI can be more energy efficient.