Concentration of High-Salinity Brine Using Single-Stage Membrane Capacitive Deionization

Concentrating saline water is essential for zero liquid discharge (ZLD) of wastewater. However, prevailing membrane-based technologies, such as reverse osmosis (RO) and electrodialysis (ED), can hardly handle high concentration differences (ΔC) in a single stage, where multi-stage operation is needed, which increases the operational difficulties and energy input. However, membrane capacitive deionization (MCDI) is theoretically applicable to high ΔC. This study explored the feasibility of employing an MCDI in brine concentrating and proposed several regulating measures on the electrode's porosity, electrical quantity for charging-discharging, and desorption conditions. Based on the determination of salt and water fluxes, these measures were confirmed to mitigate water transfer across the membrane, thereby facilitating salt transportation for brine concentrating. To address the mass imbalance between adsorbed and desorbed, a novel pre-charge strategy was designed, which enabled successful MCDI continuous operation over 50 cycles. A concentration difference of 161 g/L NaCl was achieved per single stage, which is the highest reported result among RO, ED, and MCDI studies. The concentrating rate was as high as 38.4 g/(m2·h) with a comparative energy consumption at RO and ED. This study demonstrated that MCDI is an optional technology for the future application of brine concentrating in ZLD facilities.