Fluoride removal from aqueous solution by Ca-pretreated macrophyte biomass

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Abstract
Environmental context. Fluoride concentrations in drinking water above 1.5 mg L–1 may be detrimental to human health. Many methods have been developed for removing excessive fluoride from drinking water. The use of an aquatic macrophyte biomass (Eleocharis acicularis) pretreated with Ca2+, a low-cost natural material, could be a technique for rural populations in developing countries that cannot afford treated or bottled water for daily consumption. The use of an aquatic macrophyte biomass (Eleocharis acicularis) pretreated with Ca2+ as a low-cost natural material for the removal of fluoride from aqueous solution was studied. Batch experiments were carried out to determine fluoride sorption capacity and the efficiency of the sorption process under different pH, initial F– and macrophyte biomass doses. The experimental data showed good fitting to Langmuir and Freundlich isotherm models. The maximum F adsorption capacity was 0.110 mmol g–1 with an efficiency of 64.5% (pH 6.0; 5.0 g L–1 Ca-pretreated biomass). The binding of Ca2+ to the biomass increased the removal efficiency over 100%. The F– removal kinetics were rapid, less than 30 min, and best described by the pseudo-second order rate model. The rate constant, the initial sorption rate and the equilibrium sorption capacity were determined. These results may be useful for deprived rural population water supply schemes in Mexico and in other developing countries.