Effective fluoride removal from brackish groundwaters by flow-electrode capacitive deionization (FCDI) under a continuous-flow mode

Herein, we demonstrated the suitability and effectiveness of utilizing flow-electrode capacitive deionization (FCDI) for treatment of fluoride-contaminated brackish groundwater. By comparing operational modes of short-circuited closed-cycle (SCC), isolated closed-cycle (ICC) and single cycle (SC), it was found that SCC mode was the most advantageous. In SCC configuration, the effects of different parameters on the removal of F- and Cl- were investigated including current density, hydraulic residence time (HRT), activated carbon (AC) loading and feed concentration of coexisting NaCl. Results indicated that the steady-state effluent Cl- concentration dropped with elevated applied current, and the decreasing rate got faster with the increase of HRT or AC loading. However, for the steady-state effluent F- concentration, it dropped to a value under a small applied current and maintained stable in spite of the increase in applied current, and both HRT and AC loading had insignificant effects on the steady-state effluent F- concentration. F- was preferentially removed from the treated water compared with Cl-, and a higher ion selectivity could be obtained at lower applied current and smaller HRT with the trade-off being that operation under these circumstances would generate outlet water with little change in conductivity compared to the influent. The removal efficiencies of F- and Cl- both decreased with increasing feed concentration of coexisting NaCl. This study should be of value in establishing FCDI as a viable technology for treatment of fluoride-contaminated brackish groundwater. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study demonstrated the effectiveness of utilizing flow-electrode capacitive deionization (FCDI) for treating fluoride-contaminated brackish groundwater. The study found that short-circuited closed-cycle (SCC) mode was the most advantageous operational mode. Factors such as current density, hydraulic residence time (HRT), activated carbon loading, and feed concentration of coexisting NaCl were found to affect the removal of F- and Cl-. F- was preferentially removed from the treated water compared with Cl-, and the removal efficiencies of both ions decreased with increasing feed concentration of coexisting NaCl.