Staged voltage mode in membrane capacitive deionization: Comparison with constant voltage and constant current modes

The most typical membrane capacitive deionization (MCDI) operating modes, constant voltage (CV) and constant current (CC), respectively, exhibit their own limitations on energy consumption and removal efficiency. Therefore, a staged voltage (SV) mode was first investigated as a method to take advantage of the CV and CC modes. To verify the feasibility of the SV mode, a two-staged voltage mode (2SV) was primarily operated by ascending and descending the applied voltage under various TDS concentrations of the feed solution. Then, the removal efficiency and energy consumption of the 2SV, linearly (LSV) and exponentially staged voltage (ESV) modes, were systematically estimated. From our experimental results, the applied voltage at the stage as well as the voltage difference was identified to be critical factors for both the removal and energy issues. Although the CC mode was determined to be the most energy efficient, limited removal efficiency could be the dilemma, and thus, our proposed SV mode is believed to be the most adequate strategy for MCDI operation for meeting the required water quality with lowest energy consummation.