Fluoride removal from water by electrocoagulation with aluminium electrodes: effect of the water quality

Treatment of fluoride from natural water by electrocoagulation (EC) using aluminium electrodes has been investigated in this study. The efficiency of discontinuous treatment of 10 mg F/L of two water-based fluoride solutions, after addition of sodium chloride for sufficient conductivity, has been compared. One was prepared from deionised water and the other from tap water. Although the treatment of the two solutions could be carried out with comparable electrical charge, aluminium consumption from the electrode plates depends largely on the coexisting ions. Aluminium amount dissolved on water solution depends not only on the current density but also on chloride concentration which causes electrode corrosion. Use of tap water leads to formation of inhibiting calcite film on the cathode surface due to the presence of calcium and hydrogen carbonate. At the same conductivity, treatment of tap water-based fluoride solutions required nearly two times less aluminum than that with solutions prepared with deionised water: this is to reduce the amount of aluminium sludge hydrogen carbonate-containing water, resulting in lower costs for Al plates and decreased environmental issues induced by disposal of this sludge. Experiments conducted with various current densities are discussed in terms of fluoride-over-aluminium ratio, with the support of adsorption-based EC model.