Fluoride Removal from Water by Membrane Capacitive Deionization with a Monovalent Anion Selective Membrane

Contamination of groundwater by monovalent anions, for instance, fluoride (F-) and nitrite (NO2-), leaves an adverse impact on human health. This study aims at investigating the feasibility of the application of membrane capacitive deionization (MCDI) combined with a monovalent anion permselective exchange membrane (PSM) for the removal of fluoride from water. In this study, various parameters (anion composition and concentration, pH, operating voltage, flow rate, and time) were studied for the purpose of attaining the maximum selectivity. Evaluation of the selectivity for monovalent anions was performed with the help of a lab-made MCDI with a model aqueous system (F-/SO42-). As revealed by the empirical findings, the removal of both F- and SO42- anions increased with the increase in anion concentration and pH, in addition to the increase in the selectivity for monovalent anions (F-). The removal of anions and selectivity also exhibited an increase with flow rate and operating time. Contrarily, the selectivity declined with the applied voltage. A monovalent anion selectivity of 1.43 was obtained subjected to the conditions of 1.0 V operating voltage, together with 10 min adsorption time and 30 mL/min feed flow rate. The results in this study are capable of helping develop the PSMCDI (permselective exchange membrane capacitive deionization) technology and expand its application for the removal of fluoride from drinking water.