Valorization of grape stalks into activated hydrochar for meropenem adsorption: From batch to fixed-bed column

Abstract

NaOH-activated hydrochar (HCA) derived from grape stalks was developed as a sustainable adsorbent for the removal of meropenem (MRP) from ultrapure water and simulated hospital wastewater, advancing circular-economy valorization of viticultural waste. Comprehensive characterization (SEM, FTIR, Raman, XRD, TGA) revealed that alkaline activation appeared to increase surface openness and accessibility, to enrich oxygenated surface functionalities, and to induce changes in short-range carbon ordering, enabling >95% MRP removal across pH 3–9 in batch tests. The kinetic data were best described by a pseudo-second-order model, whereas the equilibrium data followed the Langmuir model at 25 and 35 °C and the Freundlich model at higher temperatures. Adsorption was spontaneous and entropy-driven (ΔG° −7.3 to −12.5 kJ mol −1 ). FTIR, pH dependence, and speciation analysis suggest that hydrogen bonding, aromatic interactions, and pH-dependent electrostatic contributions may play a role in adsorption, corroborated by pH PZC (5.4) and molecular electrostatic potential mapping. Fixed-bed columns packed with 5 g HCA maintained C t /C 0 < 0.05 for approximately 80 min at 5 mg dm −3 in both matrices, treating 600 cm 3 over 120 min at an EBCT of 8.5 min, with the breakthrough profiles well described by the Yoon-Nelson model. A preliminary economic estimate suggests that HCA may be a cost-competitive adsorbent under the assumed lab-scale conditions.