Performance of Electrodialysis for Fluoride Removal: Using Overlimiting Current Conditions

Abstract

Water is essential for life, but contamination has become a significant global problem, particularly with groundwater, which serves as a vital source of drinking water for millions. One of the pollutants is fluoride, which, when present in high concentrations, can lead to serious health problems such as dental and skeletal fluorosis. Electrodialysis (ED) is an efficient and sustainable method to remove fluoride from contaminated water. This study investigated the application of electrodialysis (ED) under different electric current conditions to optimize fluoride removal efficiency. The study aims to evaluate fluoride removal both in monocomponent solutions, such as sodium fluoride (NaF), and in multicomponent solutions, represented by a real water sample collected from the Bambuí Aquifer in Bahia, Brazil. This dual approach allows for a better understanding of the electrodialysis performance in simplified systems, and in complex naturally occurring water matrices. The applied currents included both the conventional value commonly adopted in the literature, corresponding to 80% of the limiting current, and overlimiting current values, since operating in this regime can significantly impact the process, either positively, by reducing treatment time, or negatively, by increasing energy consumption and promoting precipitate formation, highlighting the need for careful optimization to maximize efficiency and system longevity. The results showed that operating at overlimiting currents can improve ion transport, significantly reducing treatment time by up to 37% in certain solutions. However, this increase in efficiency may be associated with a higher energy consumption and membrane fouling, particularly in multicomponent real water matrices. These findings suggest that although overlimiting currents can improve fluoride removal rate, careful optimization is required to balance energy efficiency and system longevity.