AQUEOUS FLUORIDE BIOSORPTION USING CALCIUM-SPIKED AND NON- SPIKED Moringa oleifera SEED POWDER: INFLUENCE OF DOSAGE, PARTICLE SIZE, AND PROCESS PARAMETERS

Abstract

Excessive fluoride concentrations in drinking water pose serious public health risks, including dental and skeletal fluorosis, particularly in rural, semi-arid and arid regions of developing countries where groundwater is the primary source of potable water. Traditional defluoridation methods remain costly, chemically intensive, or environmentally unsustainable, prompting the search for low-cost, eco-friendly alternatives. Moringa oleifera seed powder (MOSP) has emerged as a promising biosorbent, though its native adsorption capacity remains limited. This study aimed to enhance fluoride removal efficiency by modifying MOSP with calcium (Ca-MOSP) and to evaluate the influence of key process parameters including adsorbent dosage,particle size,pH,contact time, temperature and initial fluoride concentration; adsorption equilibrium behaviour, kinetic rates, and thermodynamic properties. Batch experiments were conducted under controlled laboratory conditions using both calcium-spiked and non-spiked MOSP to assess the effect of dosage, particle size, contact time, pH, temperature, and initial fluoride concentration. The biosorption performance was analysed using Langmuir and Freundlich isotherm models, pseudo-first-order and pseudo-second-order kinetics, and thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°), and Gibbs free energy (ΔG°). Results showed that calcium spiking significantly improved fluoride removal efficiency, with Ca-MOSP achieving over 90% removal under optimal conditions (2 g/50 mL dosage, 40 mesh size, pH 7-, and 120- minute contact time), compared to 78% for the non-spiked powder. Finer particle sizes led to increased surface area and binding site availability, while increased dosage improved performance up to a saturation threshold. Adsorption was found to be pH- dependent, with neutral pH offering the best removal efficiencies for both biosorbent types. The adsorption isotherm data fitted best with the Langmuir model, suggesting monolayer adsorption on homogeneous surfaces. Ca-MOSP exhibited a higher maximum adsorption capacity (q e = 4.98 mg/g) and affinity constant (Kₗ = 0.442 L/mg) than the non-spiked variant. Kinetic data followed the pseudo-second-order model, indicating chemisorption as the dominant uptake mechanism, with high R² values (>0.99) and strong agreement between experimental and theoretical adsorption capacities. Thermodynamic analysis confirmed that biosorption was endothermic (ΔH° = +28.45 kJ/mol for Ca-MOSP), spontaneous (ΔG° < 0), and associated with an increase in system randomness (ΔS° = +85.6 J/mol·K). Thus, calcium-modified Moringa oleifera seed powder offers a significantly enhanced, sustainable, and low-cost alternative for fluoride remediation in drinking water. The findings support its potential for practical application in areas with fluoride endemism, particularly in rural and resource-limited settings. Recommendations include adopting Ca-MOSP in decentralised treatment systems and optimising operational conditions for field deployment. Future research should explore regeneration potential, competing ion effects, and long-term performance in continuous- flow and field-scale systems.