Tuning charcoal to functional reactive filter materials for groundwater defluoridation

Abstract

Generally, the surface of a carbonaceous material is modified to increase the surface area and modulate the surface functional groups for a tailored purpose. However, the process can be highly technical, tedious, and expensive. Therefore, a simple, economical, and efficacious procedure is required to produce functional reactive filter materials for water treatment. Herein, the surface of charcoal was tinkered to boost the carbon surface oxides for high defluoridation efficiency in drinking water. Raw charcoal was modified with Piranha solution and the effects of the modification procedure on the surficial features, textural properties, elemental composition, and chemical state were determined. Using synthetic feedwater, the defluoridation efficiency of the modified charcoal was evaluated in a batch reactor to derive the process operating parameters, and the field application was tested with groundwater in a column reactor. The modification procedure had a significant impact on the defluoridation efficiency, and surficial, textural, elemental, and chemical state of the charcoal. Relative to the raw charcoal surface, the atomic concentrations of oxygen-containing functional groups (e.g., CO, O–CO, SO₄²⁺) were boosted in the modified charcoal. The pseudo-second order kinetic equation gave the best fit (r² > 0.9) to the defluoridation process, and the rate parameters K₂ (g mg⁻¹ min⁻¹) and q_e2 (mg g⁻¹) were initial fluoride concentration dependent. The defluoridation efficiency was highly susceptible to the variations in the system process variables (i.e., pH, ionic strength, anionic interference, and organic load). In the simulated field operation, significant temporal improvements in the defluoridation efficiency, pH value, and electrical conductivity were observed, and the permissible fluoride concentration of 1.5 mg L⁻¹, as recommended by the World Health Organization, was achieved.