Olives could turn out to be more than just a tasty snack or delicious pizza topping – or rather, their stones could. Often discarded in the cultivation of the olive for oil or other uses, it is estimate that every year the olive growing industry produces 4 million tonnes of olive stones as waste. Scientists at the University of Jaén and the University of Granada, both in Spain, have demonstrated a method of extracting bioethanol from the stones.
Bioethanol is a renewable source of fuel that can be produced from many kinds of waste plant matter, but it has recently come under fire. Turning fields over to growing fuel instead of food has seen grain prices rise and increased the threat of hunger. Nevertheless, the push towards bioethanol continues, with the UK government mandating that by 2010 all cars run on 5% biofuel. Thus, producing energy from an unwanted food by-product looks increasingly attractive.
The fuel was extracted by first blasting the stones with high-pressure hot water and then adding enzymes to break down the organic matter into sugars. This mixture was then fermented with yeast in order to produce ethanol, with a maximum yield of 5.7 kg per 100 kg of olive stones.
If this process could be applied to all 4 million tonnes of stones produced each year it would result in 228,000 tonnes of ethanol. Government figures for 1997 (the only ones I could find, unfortunately) indicate that 22,243,000 tonnes of petrol were sold that year. Unfortunately for olive producers, this means that waste stones would only be able to provide around a fifth of the UK’s bioethanol needs in 2010 – let alone any other countries.
It’s not all doom and gloom however. This research shows that energy can be extracted from the most unlikeliest places, and will perhaps encourage others to seek out other forms of energy from waste bio-materials.