Principal Investigator Jongyoon Han
While the conventional electrodialysis (ED) relies on bipolar ion conduction employing two ion exchange membranes, anion exchange membrane (AEM) and cation exchange membrane (CEM), our group has pro- posed unipolar ion conduction, so-called ion concen- tration polarization (ICP) desalination, employing only CEM to enhance energy efficiency. Because chloride ion, the majority salt in nature, has faster diffusivity than sodium ion, ICP desalination theoretically has a cur- rent utilization (CU) of 1.2, but the ED has only that of 1. To facilitate the ICP desalination, our group has devel- oped series of technology from Bifurcate ICP system to Trifurcate ICP (Tri-ICP) system. Here, we have developed a return flow (RF-ICP) desalination system with a newly designed flow path for improving energy efficiency.
A schematic of RF-ICP desalination system, which has three channels separated by two nano-porous membranes is shown. The three channels consist of a concentrate channel on the anodic side, a diluate channel on the cathodic side, and an intermediate channel in between. A feed solution flows through the inlet of intermediate channel with the highest pressure and flows through the outlet of both side channels with the lowest pressure. As the feed solution flows through the channels, a portion of the feed solution flows through the porous membrane (Por-flow) due to the pressure difference. The Por-flows facilitate two types of flow barriers, a suppressor for a chaotic electroconvection in the diluate stream and a preventer for a salt leakage from the concentrate stream. The remaining solution returns at the end of channel (RF-flow) and induces the effect of sweeping a mass on the CEM surfaces by shear stress.
We demonstrate that the developed RF-ICP system reduces a power consumption compared to the previously developed Tri-ICP system. Also, the RF-ICP system showed symmetrical product concentrations between diluate and concentration (data not shown), and the recovery rate increased to 50% compared to the Tri- ICP system, which was 25%. To improve the performance of RF-ICP system, more optimized system would be developed by various operating controls for recovery rate increase or spacer designs for energy efficiency increase.