New operation method of a membrane capacitive deionization system with a dual-solution mode for improving the desorption rate

Abstract

A new operation method of a membrane capacitive deionization (MCDI) system with a dual-solution mode was proposed. In this method, the concentration of the solution supplied to the cell was different during the adsorption and desorption processes. After adsorption was performed for the adsorption solution (AS) of 10 mM NaCl, desorption was performed while changing the concentration of the desorption solution (DS) to 10–70 mM. As the DS concentration increased, the discharge rate (desorption rate) linearly increased. The average discharge rates at DSs of 10 and 70 mM are 0.187 and 0.278C/g·s, respectively, which increases by approximately 1.5 times. As the DS concentration increases, the time constant (product of the electrical resistance and capacitance) of the cell decreases, resulting in an increase in the desorption rate. At the end of the desorption process, some DS remained inside the cell, reducing the charge efficiency of the subsequent adsorption process. By changing the flushing time, it was possible to control the charge efficiency and the water recovery.