Flow-electrode capacitive deionization (FCDI) is a novel electrochemical technology for water desalination and reclamation that has major advantages in energy and flow efficiencies when the electrodes are operated in short-circuited closed-cycle (SCC) mode, though little attention has been paid to a critical parameter, i.e. water recovery rate which determines the amount of brine waste generated. Results of this study show that an extremely high water recovery rate of ~95% can be achieved when desalting a 1000 mg NaCl L−1 brackish influent to a potable level of 150 mg L−1. Double current-step chronopotentiometry indicates that the decrease in energy cost is related, at least in part, to the alleviated concentration polarization at the membrane/electrolyte interface as a result of continuous regeneration of the electrode that facilitates equilibration between ion diffusion in the membranes and bulk solution. However, current efficiency further decreases with an increase in water recovery rate, which is ascribed to inevitable co-ion leakage since the flow electrodes reject salt ions with the same charge. As such, the development of membranes with higher functional densities would be in great need of.

Polarization alleviation in flow-electrode CDI enables extremely high water recovery rate in desalination and reclamation

2019 Fall National Meeting

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