Advances in electrochemical separations for desalination and resource recovery
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Electrochemical ion separation, which integrates electrochemical processes with membrane and electrode materials, represents a promising frontier in desalination, water reuse, and resource recovery. By leveraging electrochemical principles, this approach enables precise and highly selective control of ion transport, thereby contributing to water sustainability. Notably, the global semiconductor industry has experienced rapid growth in recent years, resulting in increasing resource demands and the generation of large volumes of process wastewater. In response to zero liquid discharge (ZLD) policies, semiconductor companies in Taiwan are increasingly adopting green manufacturing practices that emphasize water reuse and resource recovery. This presentation will address recent advances in electrochemical separation technologies, including membrane capacitive deionization (MCDI), redox-mediated electrodialysis (RMED), and electrochemical membrane reactors, with a focus on their underlying mechanisms, associated challenges, and performance metrics.
Membrane capacitive deionization (MCDI), which employs nanoporous carbon electrodes and ion exchange membranes (IEMs), relies on electrosorption to separate ions via the formation of electrical double layers. In particular, the incorporation of cation exchange membranes (CEMs) and anion exchange membranes (AEMs) into the separation process effectively mitigates co-ion effects and enhances both salt adsorption capacity and charge efficiency, thereby enabling the development of MCDI. As a result, MCDI offers several advantages, including high energy efficiency (TDS < 4000 ppm), high water recovery, minimal chemical additives, and environmental sustainability. We have successfully scaled up MCDI for practical applications, such as reclaimed water from municipal wastewater treatment plants and the treatment of circulating water in cooling towers and scrubbers, particularly for low- to moderate-salinity water streams. In addition, MCDI has been demonstrated for resource recovery applications, including fluoride and ammonia enrichment in high-tech industrial processes. Beyond MCDI, we have recently developed a promising electrochemical separation technology, termed redox-mediated electrodialysis (RMED). Featuring a multichannel cell architecture, RMED utilizes redox couples as electrolytes, enabling ion separation at relatively low operating voltages (< 1 V). Furthermore, we have explored strategies to enhance ion selectivity, for example toward nitrate and rare metals, by fine-tuning the functional groups in IEMs.
Future work will focus on system-level optimization to enable full-scale implementation, as well as the selective separation of pH-dependent ions, such as boron. Overall, these electrochemical and membrane technologies are well positioned to progress from pilot-scale demonstrations toward real-world commercialization.
Keywords: Electrosorption; electrodialysis; ion exchange membrane; desalination; selective separation
Dr. Chia-Hung Hou is a Professor at the Graduate Institute of Environmental Engineering, National Taiwan University. He received his bachelor’s and master’s degrees from National Taiwan University and his Ph.D. from the School of Civil and Environmental Engineering at the Georgia Institute of Technology. Dr. Hou’s research focuses on advanced carbon nanomaterials, electrochemical and membrane separations, desalination technologies (including capacitive deionization and redox-mediated electrodialysis), water reuse, and resource recovery. His research group is at the forefront of developing pilot-scale studies for innovative water technologies aimed at achieving water–energy sustainability. He has been recognized for his outstanding research contributions with several honors, including the Academic Research Award from the National Science and Technology Council (Taiwan). In addition to his research activities, Dr. Hou has held various international roles, including serving as a committee member of the International Working Group on CDI & Electrosorption, a management committee member of the International Water Association (IWA) Membrane Technology Specialist Group, an editor for Desalination and Water Treatment and the Journal of Environmental Chemical Engineering, and a member of the editorial board of Desalination.