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Per- and polyfluorinated alkyl substances (PFAS) are persistent contaminants that have been continuously detected in groundwater and drinking water around the globe. Hexafluoropropylene oxide dimer acid (tradename GenX) has been used to substitute traditional PFAS, such as PFOA, but its intense use has caused widespread occurrence in water streams and often in high levels. Here, we evaluate a redox-copolymer, poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl- co -4-methacryloyloxy-2,2,6,6-tetramethylpiperidine) (PTMA- co -PTMPMA), for the selective electrochemical removal of GenX. The amine functional groups promote affinity towards the anionic PFAS, and the redox-active nitroxide radicals provide electrochemical control for adsorption and desorption. Faster kinetics and higher uptake (>475 mg g −1 adsorbent) were obtained with the redox-copolymer when applying 0.8 V vs. Ag/AgCl potential compared to open circuit. The copolymer electrosorbents were evaluated over a wide pH range and diverse water matrices, with electrostatic-based mechanisms dependent on the state of protonation of the PFAS. Moreover, we translated the redox-electrodes from a batch to flow-by cell configuration, showing successful adsorption and release of GenX under flow and electrochemical control. Finally, prolonged exposure of GenX at reduction potentials generated smaller PFAS fragments at the redox-electrodes. To fully defluorinate GenX, the copolymer-functionalized electrodes were coupled with a boron-doped diamond (BDD) counter electrode for integrating separation and defluorination within the same device. The combined system demonstrated close to 100% defluorination efficiency. Thus, we highlight the potential of electroactive redox platforms for the reactive separation of fluorotelomers, and point to future directions for their practical implementation for water treatment. 

Treating toxic monovalent anions such as NO 3 − or ClO 4 − 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 m 3 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 NO 3 − , 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 m 3 .