Valorization of crude olive stone in the removing of polyphenols from crude olive mill wastewater: kinetic, isotherm and mechanism study

Removal of polyphenols from crude olive mill wastewaters (COMWW) is vital to the development of olive industries. In addition, the exploitation of the residue of the olive oil industry such as crude olive stone (COS) constitutes a valorization of this substance and makes a contribution to the fight against environmental pollution. For this purpose, this study concerns the utilization of COS as an adsorbent of polyphenols from COMWW. The characterization of COS was realized by FTIR, XRD, SEM, PZN, BET and TGA-DTA. The adsorption kinetics and isotherms of polyphenols was analyzed by pseudo-first-order (PFO), pseudo-second-order (PSO), intraparticle diffusion models (MW) and nonlinear models of isotherms Langmuir (LM) and Freundlich (FM) respectively. This study goal at understanding the adsorption mechanism of polyphenols on COS by FTIR and XRD study. The results of adsorption kinetics demonstred that the adsorption capacity of polyphenols ‘PP’ onto COS is decreased from 381 mg g(−1) to 235 mg g(−1), with the increasing of the temperature, from 25 °C to 45 °C, indicating an exothermic process, which is confirmed by the negative values of enthalpy ΔH°. Moreover, the negative values of free energy ΔG° and entropy ΔS° indicate the spontaneous and ordered adsorption phenomenon. Kinetic and isotherms studies showed that polyphenols adsorption onto crude olive stone followed PSO kinetic, the FM and LM models were the best fitted. Consequently, this study indicates that crude olive stone could be used as a cheap adsorbent for removing of polyphenols from crude COMWW.