Operational Control of Fluoride Removal Using Calcium-Modified <i>Moringa </i><i>Oleifera</i> Seed Powder: Influence of Dosage and Particle Geometry

Adsorption-based separation processes continue to attract scientific interest as low-energy strategies for modifying aqueous chemistry under resource-limited conditions. Within this context, plant-derived materials offer a flexible platform for turning surface reactivity through simple chemical and physical modifications. This study examined how calcium modification and particle-scale control influence fluoride uptake behaviour in <i>Moringa oleifera</i> seed powder (MOSP), with emphasis on operational performance rather than material synthesis. Batch experiments were conducted to quantify fluoride removal efficiency, residual fluoride concentration, and adsorption capacity using calcium-spiked and non-spiked MOSP across a range of adsorbent dosages, particle sizes, and mesh size classifications. Statistical analysis demonstrated that adsorbent dosage significantly affected all fluoride removal indicators (p < 0.001). Increasing dosage enhanced overall fluoride removal efficiency while reducing mass-normalised adsorption capacity, indicating distinct scaling behaviour between system-level removal and material-level uptake. Physical structuring of the adsorbent exerted a strong influence on performance. Finer particle fractions consistently produced higher removal efficiencies and lower residual fluoride concentrations than coarser fractions, a trend confirmed using both particle size and mesh size classifications. Interaction mapping revealed that fluoride removal efficiency was maximised under combined conditions of fine particle size and moderate-to-high dosage, particularly for calcium-spiked MOSP. In contrast, non-spiked MOSP exhibited a narrower operational window, with reduced performance across most dosage-particle size combinations. Across all experimental conditions, calcium-spiked MOSP outperformed the unmodified material, achieving higher removal efficiencies and lower residual fluoride concentrations. These results demonstrate that fluoride removal using MOSP is not solely dependent on chemical composition but is strongly governed by operational configuration. The findings highlight the importance of integrating chemical modification with particle-scale optimisation when designing adsorption-based water treatment systems. Calcium-modified <i>Moringa oleifera</i> seed powder therefore represents a scientifically tractable and operationally adaptable material for fluoride control in decentralized and low-infrastructure environments.