Unraveling the mechanism of phenol removal from olive mill wastewater using activated olive pomace in semi-industrial fixed-bed system: a DFT and experimental study

Abstract

This study investigates phenol adsorption from olive mill wastewater (OMW) by a semi-industrial fixed-bed system filled with activated olive pomace (AOP). The adsorption process was modeled with the Homogeneous Surface Diffusion Model (HSDM), accounting for both adsorption equilibrium and mass transfer kinetics. Experiments were conducted at a flow rate of 2 mL min⁻¹, a bed height of 47 cm, and an initial phenol concentration of 5693 mg L⁻¹. COMSOL Multiphysics 6.0 was used to solve the advection–dispersion equation with linear and Langmuir models, showing good agreement with breakthrough curves. The residual mean square error was less than 0.3, indicating reliable model validation. Key mass transfer coefficients were k_f = 7.21 × 10⁻⁶ m s⁻¹, D_s = 2.41 × 10⁻⁶ m² s⁻¹, and D_L = 3.53 × 10⁻¹ m² s⁻¹. The adsorption capacity reached 1471 mg g⁻¹, demonstrating the effectiveness of olive pomace as a cost-efficient adsorbent for industrial effluents. Recycling and elution tests confirmed the viability of this adsorption technology for large-scale use. Density Functional Theory (DFT) calculations at the B3LYP/6-311G(d,p) level were performed to provide molecular-level insight into the potential active sites and adsorption interactions of the AOP. A techno-economic study was conducted to evaluate the feasibility and economic viability of the project, confirming the validity of the proposed approach for semi-industrial-scale application.