Upcycling Orange-Derived Peel and Bagasse into ZnCl₂‑Activated Biochar for Sustainable Enrofloxacin Removal

The sustainable management of agro-industrial residues, aligned with the United Nations Sustainable Development Goals (SDGs), has emerged as an effective strategy for mitigating environmental impacts and enabling low-cost environmental technologies. In this context, a ZnCl₂-activated biochar was synthesized from orange peel and orange bagasse agro-industrial residues and evaluated for the removal of emerging contaminants from aqueous systems, using enrofloxacin as a model compound. The activated biochar exhibited a high fixed carbon content (63.1 wt %) and ash content of 14.74 wt %, along with a decrease in the H/C and O/C atomic ratios compared to the raw biomass, indicating increased carbonization and aromaticity. FTIR analysis showed the loss of oxygenated (O-H and C-O) and aliphatic groups after pyrolysis, along with the emergence of aromatic C=C structures, indicating increased aromaticity. The biochar showed a remarkable increase in specific surface area, reaching 1140 m² g^-1, compared to 0.475 m² g^-1 for the precursor biomass. SEM analyses revealed a rough, fragmented, cavity-rich surface morphology. XRD confirmed the predominantly amorphous structure of the biochar. Adsorption assays demonstrated nearly complete enrofloxacin removal, with kinetics well described by the Elovich model and equilibrium data fitting the Freundlich isotherm. The biochar also maintained satisfactory performance in the presence of interfering species commonly found in lagoon water. Overall, these results highlight the strong potential of citrus-waste-derived activated biochar as a sustainable adsorbent for emerging contaminant removal, contributing to agro-industrial waste valorization and the development of water treatment technologies aligned with the SDGs.