Aluminium hydroxide impregnated sawdust adsorbent: An eco-friendly and low-cost strategy for defluoridation of water

Abstract

Environment-friendly and cost-effective adsorbent is necessary for removal of excess fluoride from water to control the spread of fluorosis among people in fluoride-rich area. Plant-based cellulosic materials are the preferred choice for this purpose. In this work, aluminium hydroxide impregnated sawdust (AHSD) adsorbent has been prepared, characterized and applied for defluoridation of water through batch and fixed-bed adsorption. Fluoride adsorption capacity of AHSD in batch adsorption experiment is 4.45 mg/g for the initial fluoride concentration between 5-50 mg/L. At low fluoride concentration, the Freundlich isotherm model fit reasonably well, while at higher fluoride concentration (> 40 mg/L) the Langmuir model show better fitting with the experimental data. The adsorption kinetics follow pseudo second-order kinetic model. In fixed-bed column adsorption, 4 g of the adsorbent is capable of bringing down the fluoride concentration from 5 mg/L to < 1.5 mg/L (WHO limit) for 690 mL of contaminated water. Residual aluminium in the treated water was within permissible limit of WHO. The reasonably good adsorption capacity and effectivity in both batch and fixed-bed column adsorption suggests that AHSD is an environment-friendly, cost-effective and promising adsorbent for defluoridation of water.