Electro-osmosis-based electrodialysis without concentrate recirculation for direct recovery of high-concentration...

Water transport by electro-osmosis (EO) and osmosis (OS) in electrodialysis (ED) is generally considered a limitation because it dilutes the concentrate stream and restricts the production of highly concentrated brines. In this study, a novel electro-osmosis-based electrodialysis (EO-ED) process was developed and experimentally validated, in which water transport is utilized as the driving force for concentrate discharge without concentrate recirculation. The desalination performance and water transport behavior of EO-ED were evaluated using Na₂SO₄ solutions under various operating conditions. Stable desalination and concentrate recovery were achieved without a concentrate circulation pump. The estimated EO water transport remained nearly constant, whereas the estimated OS water transport strongly depended on the concentration gradient and operating time. Increasing the current density or cell voltage reduced the cumulative OS water transport at a given cumulative charge by shortening the operating time, resulting in lower water-to-salt transport ratios and higher concentrate concentrations. A maximum discharged concentrate concentration of 287 g/L was obtained during extended operation, while current efficiency remained above 92.8%. Although EO-ED exhibited slightly higher electrical resistance than conventional ED, comparable current efficiencies were maintained. These results demonstrate the feasibility of EO-ED as a new non-recirculating ED configuration that utilizes membrane water transport for concentrate discharge while simplifying the process configuration.