Olive Leaf Waste from the Olive Oil Industry as Adsorbent Material for the Removal of Methylene Blue from Water

In this study, olive mill leaves (OMLs), a waste generated during the olive cleaning at the mill, were used as an adsorbent for removing methylene blue (MB) from aqueous solution. An Olive Leaf-based Adsorbent (OLA) was prepared from OMLs with minimal processing. The maximum adsorption capacity experimentally measured for OLA was qe = 12.8 mg∙g−1. The adsorption of MB by OLA, primarily governed by electrostatic attraction, pore diffusion and weak interactions with functional groups of the leaves, is well described by the Koble–Corrigan isotherm model and pseudo-second-order kinetic model. The performance of OLA under practical environmental conditions, such as in synthetic wastewater, remained unchanged compared to tests carried out in ideal conditions. The possibility of regenerating OLA with methanol, HCl and NaCl solutions was demonstrated, allowing the material to be reused for at least three cycles with unchanged performance. A life cycle assessment was conducted to compare the impacts of OLA production with those of activated carbon, a benchmark for adsorbent materials. Overall, despite its moderate adsorptive performance, OLA stands out as a highly sustainable material for dye removal from polluted waters, owing to its exceptional cost-effectiveness, reusability, and minimal environmental impact.