Performance, mechanism, and reusability of agri-food waste derived-bioadsorbent for an azo dye removal from tannery wastewater in batch and fixed-bed systems

The growing demand for sustainable and low-cost wastewater treatment technologies has intensified interest in lignocellulosic bioadsorbents derived from agricultural residues. In this study, a novel composite bioadsorbent based on olive pomace and date seeds (OPDS) was developed and evaluated for the removal of the anionic dye Acid Green 25 (AG 25) in both batch and fixed-bed column systems. SEM analysis revealed a heterogeneous, rough, and porous surface morphology, while BET characterization indicated a mesoporous structure with slit-shaped pores and a specific surface area of 1.83 m 2 g -1 , consistent with the raw, unactivated nature of the material. FTIR analysis confirmed the presence of abundant surface functional groups, including hydroxyl, carboxyl, and carbonyl moieties, which play a key role in dye binding through electrostatic attraction, hydrogen bonding, and π–π interactions. Batch adsorption experiments showed optimal performance at pH 2, a contact time of 120 min, and a temperature of 288 K. Equilibrium data were best described by the Liu isotherm, yielding a maximum adsorption capacity of 9 mg g -1 , while kinetic data followed the Elovich model, indicating chemisorption on a heterogeneous surface. Thermodynamic parameters confirmed that the adsorption process is spontaneous and exothermic, with enhanced favorability at lower temperatures. Fixed-bed column studies demonstrated that adsorption efficiency is governed by hydrodynamic and chemical parameters such as flow rate, influent concentration, pH, bed height, and column diameter, with breakthrough behavior well predicted by the Yan–Viraraghavan model. Furthermore, OPDS exhibited excellent regeneration performance over multiple adsorption–desorption cycles, highlighting its potential as an efficient, sustainable, and reusable bioadsorbent for the treatment of dye-contaminated wastewater.