Sustainable Biochars from Agri-Food Residues for the Selective Removal of Pharmaceuticals: Performance Under Untreated Wastewater Conditions

In this study, biochars derived from agri-food wastes, including different avocado residues (peel- and seed-derived fractions), olive pits and cherry stones, were evaluated as low-cost and sustainable adsorbents for the removal of the emerging contaminants sulfamethoxazole (SMX), antipyrine (ANT) and trazodone (TRZ) from aqueous solutions. Despite their very low BET surface areas, the biochars exhibited notable adsorption capacities, indicating that adsorption performance was mainly governed by surface chemistry rather than textural properties. FTIR analysis confirmed the presence of abundant oxygen-containing functional groups on the biochar surfaces, enabling electrostatic interactions, hydrogen bonding and dipole–dipole interactions with the target contaminants. Adsorption kinetics for all systems were well described by the pseudo-first-order model, with equilibrium capacities closely matching experimental values, suggesting rapid and reversible surface interactions. Intraparticle diffusion analysis revealed that diffusion was not the sole rate-limiting step, with external mass transfer and surface interactions dominating the initial adsorption stage. Equilibrium isotherm analysis showed that SMX and ANT adsorption onto avocado-derived biochars followed the Langmuir model, whereas TRZ adsorption was better described by the Freundlich model. In contrast, olive pit biochar exhibited a markedly higher affinity for TRZ, achieving near-complete removal and fitting the Langmuir isotherm. Finally, high removal efficiencies were maintained when applying the selected biochar to real municipal wastewater, demonstrating robustness under complex matrix conditions. Overall, the results highlight the potential of these agri-food waste-derived biochars, including multiple avocado fractions, as sustainable and economically viable adsorbents for quaternary wastewater treatment.