Mechanochemical-assisted Natural Deep Eutectic Solvent as a platform for an olive leaves biorefinery: Extraction of bioactive compounds and methane production

This study introduces an innovative biorefinery process aimed at maximizing the utilization of olive leaves. The proposed approach seeks to extract valuable phenolic compounds, lignocellulosic material, and biomethane from olive leaves. To achieve this, a combined technique involving mechanochemical extraction and sustainable solvents, specifically natural deep eutectic solvents (NADES), was employed. Unlike conventional methods, NADES were simultaneously formed and utilized for extraction within a ball mill. The optimal conditions for maximum extraction of high-value compounds were 0.5 g of OL using 10 mL of ChCl:Gl (3:1) and 1.1 h in a ball mill. The recovered yields were 14.5 ± 2.9 g/kg OL of lignocellulosic fraction and 1.3 ± 0.3 g gallic acid eq./kg OL of phenolic compounds. OL waste generated after the optimized extraction process was evaluated for methane production, obtaining 142 ± 53 mL CH4/g VS OL waste compared to 126 ± 30 mL CH4/g VS untreated OL. Therefore, NADES represent promising solvents for the biorefinery process and reduce dependence on organic solvents.