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

Olive leaves, a massive byproduct of olive oil production, are about to become a goldmine of valuable compounds and renewable energy—thanks to a simple ball mill and a green solvent.

Imagine turning agricultural waste into a treasure trove of bioactive compounds and biomethane. That's exactly what researchers in Spain have achieved with olive leaves, a byproduct of olive oil production. They developed an innovative biorefinery process that maximizes the value of this waste by extracting phenolic compounds, lignocellulosic material, and producing methane—all in one go.

The secret lies in a combined technique: mechanochemical extraction using natural deep eutectic solvents (NADES). Unlike conventional methods, NADES are formed and used simultaneously inside a ball mill. The optimal conditions were surprisingly simple: just 0.5 grams of olive leaves, 10 mL of a choline chloride:glucose mixture (3:1), and 1.1 hours of milling. This yielded 14.5 ± 2.9 g/kg of lignocellulosic fraction and 1.3 ± 0.3 g gallic acid equivalents per kg of phenolic compounds.

But the story doesn't end there. The leftover olive leaf waste was then tested for methane production. It produced 142 ± 53 mL CH4 per gram of volatile solids—a slight improvement over the 126 ± 30 mL from untreated leaves. This shows that NADES not only boost extraction efficiency but also enhance the energy potential of the residual biomass.

This research highlights the promise of NADES as a sustainable platform for biorefineries, reducing our reliance on harmful organic solvents. It's a win-win for the environment and the circular economy.

Key Points

• NADES formed in ball mill extract olive leaf compounds efficiently.
• Optimal: 0.5 g OL, 10 mL ChCl:Gl (3:1), 1.1 h.
• Methane yield increased from 126 to 142 mL CH4/g VS.