Effects of Adsorbent Dosage and Particle Size on Fluoride Removal Using Calcium-Spiked Moringa oleifera Seed Powder

Abstract

Access to safe drinking water remains a major challenge in fluoride-endemic regions, where excessive fluoride concentrations can lead to dental and skeletal fluorosis. This study evaluated the effects of adsorbent dosage, particle size, and particle size classification (mesh size) on the fluoride removal performance of Moringa oleifera seed powder (MOSP) in both calcium-spiked and non-spiked forms. A three-factor factorial batch adsorption experiment was conducted using initial fluoride concentration of 1ppm, dosages of 0.25–2.0 g/100 mL, particle sizes of <250 μm, 250–500 μm, and >500 μm, and mesh classifications of 20 (850 μm), 40 (425 μm), and 60(250 μm). Response variables included fluoride removal efficiency, residual fluoride concentration, and adsorption capacity (qe), measured using a fluoride ion-selective electrode. ANOVA and linear regression were applied to evaluate the dose and size response relationships. Results showed that calcium-spiked MOSP consistently outperformed non-spiked MOSP across all parameters. Fluoride removal efficiency increased with dosage, reaching 88.95% for spiked and 70.34% for non-spiked MOSP at 2.0 g. Finer particle sizes and smaller mesh fractions significantly enhanced removal efficiency and reduced residual fluoride levels, with spiked MOSP at ≤250 μm achieving 89.80% removal and residual fluoride below WHO guidelines. Regression analysis confirmed strong inverse relationships between particle size/mesh size and fluoride removal performance, and positive correlations with dosage. The improved performance of calcium-spiked MOSP is attributed to increased surface-active Ca2+ sites enabling precipitation of CaF2 and enhanced adsorption via electrostatic attraction and ion exchange. These findings indicate that calcium-spiked MOSP, optimally prepared at fine particle size and moderate dosage, is a viable, locally sourced defluoridation medium suitable for rural water treatment systems.