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35 בריאות, חקלאות וסביבה Integrating Divalent-Selective Electrodialysis in Brackish Water Desalination L i or Monat1 , Ru L i u1 , Menachem Elimelech2, Oded Nir1* 1. Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sde Boker Campus, Midreshet Ben- Gurion, Israel 2 . D e p a r t me n t o f C h em i c a l a n d Environmental Engineering, Yale University, New Haven, Connecticut, United States Keywords: Ion-ion selectivity, selective ion- exchange membranes, reverse osmosis pretreatment , reverse osmosis post- treatment, circular desalination. Introduction.Brackishwater(BW)desalination is an alternative source of freshwater in inland areas. Reverse osmosis (RO) is the dominant desalination technology but is limited due to high-salinity brine production and depletion of essential minerals for human health and plant growth in the low- salinity permeate. Electrodialysis (ED) is an alternative desalination technique, driving the ions through ion-exchange membranes under applied voltage. Separation between counter-ions depends on the membranes’ characteristics and operational parameters. Most studies, specifically BW desalination, focus on monovalent-selective ED. Our proposed novel approach (Figure 1) integrates divalent-selective ED (DVS-ED) with BWRO desalination. DVS-ED can transfer divalent ions directly from BW feed into the BWROpermeate, therefore gaining two goals: (1) supplementing the desalinated water with essential minerals and (2) decreasing the scaling potential in the RO step, thus increasing water recovery and reducing the brine volume. Experimental/methodology. Electrodialysis batch experiments with natural brackish water to track ions and water transport were conducted under varied constant current using different cation-exchange membranes. The diluate water quality was analyzed according to standards and regional regulations. Techno-economic analysis was conducted based on the experimental results to assess the practical. Results and discussion. The applied current significantly influenced the selectivity between mono- and divalent catios, promoting divalent selectivity in low current density. The DVS-ED enabled the desired high-quality water for domestic and agricultural uses of desalinated water while reducing the scaling potential in the BWRO step and minimizing the brine volume by 20%. This result demonstrates the potential of DVS-ED as a dual-function pretreatment and post-treatment step. The DVS-EDprocess cost (considering the main components – electricity and capital costs) was 4-21% BWRO desalination cost, enabling reduced scaling potential and remineralization of the BWRO permeate without external chemical addition. The capital costs of ion-exchange membranes contributedmost significantly to the overall cost, emphasizing the critical need for cheaper and more selective membranes. Our results call for more research directed to divalent-selective membranes for ED appilcations.