Emerging investigator series: Capacitive deionization for selective removal of nitrate and perchlorate: Impacts of ion selectivity and operating constraints on treatment costs

Treating toxic monovalent anions such as NO₃^- or ClO₄^- in drinking water remains challenging due to the high capital and environmental costs associated with common technologies such as reverse osmosis or ion exchange. Capacitive deionization (CDI) is a promising technology for selective ion removal due to high reported ion selectivity for these two contaminants. However, the impacts of ion selectivity and influent water characteristics on CDI life cycle cost have not been considered. In this study we investigate the impact of ion selectivity on CDI system cost with a parameterized process model and technoeconomic analysis framework. Simulations indicate millimolar concentration contaminants such as nitrate can be removed at costs in the range of $0.01-0.30 per m³ at reported selectivity coefficient ranges (S = 6-10). Since perchlorate removal involves micromolar scale concentration changes, higher selectivity values than reported in literature (S > 10 vs. S = 4-6.5) are required for comparable treatment costs. To contextualize simulated results for CDI treatment of NO₃^-, CDI unit operations were sized and costed for three case studies based on existing treatment facilities in Israel, Spain, and the United States, showing that achieving a nitrate selectivity of 10 could reduce life cycle treatment costs below $0.2 per m³.