Fluoride uptake characteristics of activated carbon from agricultural-waste

Removal of excess fluoride from ground water to within the permissible limits of 1.0-1.5 mg/L is the only way to control fluorosis. Batch and column type experiments were carried out for the adsorption of fluoride using activated carbon prepared from palm seed coat (PSCC) by dolomite process. In the batch study, influence of pH, adsorbent dose, contact time and initial fluoride concentration was investigated. Adsorption of fluoride was pH dependent and higher removal efficiencies were observed in the pH range of 4-8. Fluoride removal increased with dosage of carbon. A low concentration aluminium sulphate solution (2 per cent) effectively regenerated the exhausted carbon bed. The adsorption process obeyed Freundlich adsorption isotherm. The kinetic studies revealed that the forward rate constant was comparatively much higher than the backward rate constant. Continuous flow experiments in fixed bed columns were carried out with ground water in order to assess the feasibility of this carbon for field application. The performance of the carbon in fluoride removal was studied as a function of flow rate, initial fluoride level and particle size of the adsorbent. Fluoride removal increased with decreasing particle size of the carbon. The interesting feature of the study was that the defluoridation capacity increased with increase in the initial fluoride ion concentration. The pH, total alkalinity, total hardness, total dissolved solids of the treated water did not change appreciably indicating success of this technique for field application.