Adsorptive removal of fluoride using biochar - A potential application in drinking water treatment

Fluoride as a geogenic contaminant is commonly encountered in groundwater-based drinking water sources. In the present study Watermelon Rind (Citrullus lanatus) Biochar (WMRBC) was investigated for its defluoridation potential. The factors affecting the removal of fluoride, including pH, adsorbent dosage, initial concentration, and contact time were investigated. The experimental data were fitted well by Freundlich isotherm and pseudo-second-order model, the maximum fluoride adsorption capacity being 9.5 mg/g. Thermodynamic parameters indicated that the fluoride adsorption process was a spontaneous exothermic process. The presence of other anions like HCO3- , CO32- , Cl- , SO42- , and NO3- (100 mg/L) had little effect on the adsorption of fluoride at 50 mg/L. Characterization studies of WMRBC before and after fluoride adsorption by SEM, ATR, EDX and XRD techniques, indicated that the adsorption of fluoride may be by electrostatic attraction through protonated basic functionalities present in WMRBC and by precipitation at the mineral sites. WMRBC could be a viable adsorbent for effective removal of fluoride from drinking water and industrial wastewater.