Adsorption–desorption of phenolic compounds from olive mill wastewater using a novel low-cost biosorbent

Several materials have been investigated for the adsorption of olive mill wastewater phenolic compounds. However, researchers have focused on the development of novel, low-cost, with high adsorption capacity adsorbents, originated from the food industry as by-products. The aim of this work was the investigation of the effectiveness of a juice industry by-product, pomegranate seed, for the adsorption of olive mill wastewater phenols. Furthermore, chemical activation and thermal activation of the adsorbent took place in order to improve total phenols uptake and afterwards, desorption process in hydrochloric acid was studied. After the determination of equilibrium time, the effects of temperature (20–60 °C), solution’s pH (4.0–8.0), initial sorbate concentration (50–500 mg/L), sorbent mass concentration (0.01–0.05 g/mL OMW), and sorbent particle size (0.149–1.180 mm) on adsorption yield were studied performing batch experiments. The maximum phenols uptake observed was 92.8% after 10 min, at 30 °C and a pH of 5.0, with an initial sorbate concentration of 162.5 mg/L, a sorbent mass concentration of 0.02 g/mL, and a sorbent particle size of 0.922 mm. Langmuir, Freundlich, and Temkin isotherms were developed for the equilibrium description, while pseudo-first-order, pseudo-second-order, and intra-particle diffusion models were applied to investigate adsorption kinetics. The experimental data were best fitted to the Langmuir model, whereas the kinetic data followed the pseudo-first-order kinetic model. The results of the study were promising indicating that pomegranate seed could be used as a novel and low-cost biosorbent.