Removal of antiviral favipiravir from wastewater using biochar produced from hazelnut shells

Abstract Increasing drug pollution represents a substantial risk to the safeguarding of water resources. Favipiravir, a commonly used antiviral medication, is one of the pharmaceutical residues found in wastewater and poses a threat to the ecosystem. Favipiravir is classified as Category 2 for germ cell mutagenicity and reproductive toxicity and is a drug suspected of leading to genetic abnormalities and adverse effects on the developing fetus. In this study, hazelnut shell-derived activated carbon was utilized as an adsorbent for the removal of favipiravir from aqueous solutions. First, the produced activated carbon was characterized through various analyses. Then, during the adsorption process, key parameters such as initial favipiravir concentration, adsorbent dosage, solution pH, contact time, and temperature were optimized. The process was analyzed based on equilibrium, kinetics, and thermodynamics. Optimum conditions (30 μg/mL initial concentration, 15 mg adsorbent dose, 90 min contact time, pH 2) were determined, and the highest adsorption efficiency of 94.60% was obtained under these conditions. The adsorption mechanism was most accurately by the pseudo-second-order rate model ( R ²: 0.9998) and the Langmuir adsorption model ( R 2 : 0.9942). Moreover, thermodynamic studies have shown that the mechanism is spontaneous since the free energy change (Δ G < 0), exothermic since the enthalpy change (Δ H < 0), and the entropy change (Δ S < 0) reduce the disorder in the system. This study emphasizes the adsorbent’s potential as a green and economical treatment solution.