Activated-hydrochar derived from olive mill wastes for the removal of phenolic compounds from olive mill wastewater

In the present study, high-quality activated carbons (ACs) were prepared from a mixture of olive stones and olive mill wastewater (OMWW) through successive hydrothermal carbonization (HTC) and potassium hydroxide (KOH) activation. Textural, morphological, and chemical characteristics of hydrochar (HC) and derived ACs, produced using two KOH/HC ratios (2 and 4), were investigated. KOH activation improved the porous structure of HC and its surface functionality. The best properties were obtained for HC activated by KOH at a ratio of 2 exhibiting a promising surface area (≈1000 m²/g) and high adsorptive properties towards methylene blue and iodine (617 and 1203 mg/g, respectively). Batch tests were performed to explore the ability of the produced ACs in removing phenolic compounds (PCs) from OMWW, while investigating the effect of contact time, pH, and PCs initial concentration on the adsorption process. The higher removal efficiency was obtained at a pH of 10 after ~ 4 h of contact time. The adsorption kinetic data are well described by the pseudo-second-order kinetic model, while the isotherm adsorption data were found to fit both Langmuir and Freundlich isotherm models. HTC of olive mill wastes followed by KOH activation could be a promising method to produce AC with high porosity and promising potential to remove PCs from OMWW.