Fluoride\nRemoval from Brackish Groundwaters by Constant\nCurrent Capacitive Deionization (CDI)

Abstract

Charging capacitive\ndeionization (CDI) at constant voltage (CV)\nproduces an effluent stream in which ion concentrations vary with\ntime. Compared to CV, charging CDI at constant current (CC) has several\nadvantages, particularly a stable and adjustable effluent ion concentration.\nIn this work, the feasibility of removing fluoride from brackish groundwaters\nby single-pass constant-current (SPCC) CDI in both zero-volt and reverse-current\ndesorption modes was investigated and a model developed to describe\nthe selective electrosorption of fluoride and chloride. It was found\nthat chloride is preferentially removed from the bulk solution during\ncharging. Both experimental and theoretical results are presented\nshowing effects of operating parameters, including adsorption/desorption\ncurrent, pump flow rate and fluoride/chloride feed concentrations,\non the effluent fluoride concentration, average fluoride adsorption\nrate and water recovery. Effects of design parameters are also discussed\nusing the validated model. Finally, we describe a possible CDI assembly\nin which, under appropriate conditions, fluoride water quality targets\ncan be met. The model developed here adequately describes the experimental\nresults obtained and shows how change in the selected system design\nand operating conditions may impact treated water quality.