Electrocoagulation as an affordable technology for decontamination of drinking water containing fluoride: A critical review

This review addresses the removal of fluoride contained in different natural groundwater samples from various parts of the world using the electrocoagulation (EC) process. A detailed analysis of different metals (Fe, Al) and Al alloys used as sacrificial electrodes is carried out. The best performance in removing high concentrations of fluoride from natural groundwater (2–10 mg L−1), until fulfilling the World Health Organization (WHO) recommendation (<1.5 mg L−1), is obtained using aluminum and aluminum alloys. The fluoride removal occurs through the substitution of a fluoride ion by a hydroxyl group from aluminum flocs, highlighting that the presence of coexisting ions such as hydrated silica, sulfates, phosphates, bicarbonates, magnesium, calcium, and so on, do not impede the fluoride removal. On the other hand, the modest removal of fluoride with iron impedes satisfy the WHO guideline. Total operating costs for the removal of fluoride with Al electrodes are between 0.38 and 0.62 USD m−3. Among the different continuous EC reactors, those with parallel plates stand out, because they allow control the flow rate and the wear of the electrodes is uniform, in addition to being relatively easy to scale-up. The importance of mathematical modeling and the use of computational fluid dynamics (CFD) simulations to understand the EC process and design smart reactors is also analyzed. Finally, an in-depth analysis of EC’s scientific challenges in the treatment of groundwater contaminated with fluoride is presented.