Green Approach to Ampicillin Removal: Modified Rice Husk as a Sustainable Adsorbent

Widespread occurrence of the antibiotic ampicillin in water bodies, due to incomplete removal by conventional treatments, contributes to antimicrobial resistance and environmental risks. This study evaluated the adsorption performance of acid-treated rice husk (ARH) for the removal of ampicillin from industrial wash off, incorporating kinetic, thermodynamic, and statistical optimization frameworks. Rice husk was treated with tetraoxosulphate (VI) acid (H2SO4), noted as ARH and then characterized for surface functional groups and morphology. Experiments were carried out by varying three adsorption factors: adsorbent dosage (1 to 5g), contact time (29.3 to 180min) and ampicillin concentration (1 to 5mg/mL). Adsorption experiment was designed using the central composite design (CCD) of the response surface methodology (RSM). Experiments were carried out for optimization, equilibrium isotherm, kinetics and thermodynamic studies. The adsorption kinetics aligned closely with the pseudo-second-order model (R² = 0.9964). Thermodynamic analysis confirmed the process to be both spontaneous and exothermic, characterized by a negative enthalpy change (ΔH° = –21.17 kJ/mol) and consistently negative Gibbs free energy values suggesting favourable adsorption. Ampicillin concentration and ARH dosage were identified as the most statistically significant parameters influencing removal efficiency. The developed quadratic model exhibited high predictive reliability (R² = 0.9660, P < 0.001) with low significant lack-of-fit, supporting its robustness. Optimization analysis predicted a maximum removal efficiency of 94.99% under the conditions of 181 minutes contact time, 1.0 g/L ARH dosage, and 4.47 mg/L initial concentration, achieving a desirability score of 1.000. These findings underscore the efficacy of ARH as a sustainable, low-cost biosorbent for the treatment of pharmaceutical-laden wastewater, demonstrating high performance under carefully optimized conditions and strong potential for scalable environmental applications.