Turning Waste Olive Stones Into Bioethanol

Olive stones (pits) could be the newest ethanol feedstock used in Spain and could give the olive processing industry an opportunity to turn the 4 million tons of olive stones it generates every year into a valuable asset.

Researchers from the Universities of Jaén and Granada have now shown how this can be achieved in a study published in the latest edition of the Society of Chemical Industry’s (SCI) Journal of Chemical Technology & Biotechnology.

The olive stone, removed when processing raw olives for use as olive oil and table olives, makes up around a quarter of the total fruit. It is rich in polysaccharides (cellulose and hemicellulose) that can be broken down into sugar and then fermented to produce ethanol.

The team pre-treated olive stones using high-pressure hot water then added enzymes that degrade plant matter and generate sugars. The hydrolysate obtained from this process was then fermented with yeasts to produce ethanol. Yields of 5.7 killograms (kg) of ethanol per 100kg of olive stones have been reached.

“The low cost of transporting and transforming olives stones make them attractive for biofuels,” said Sebastián Sánchez, a researcher in the Department of Chemical, Environmental and Materials Engineering at the University of Jaén.


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