Researchers at Aston University in the UK have produced high-grade biodiesel from growing microalgae on leftover coffee grounds.

Approximately 98 million cups of coffee are drunk just in the UK every day, resulting in vast quantities of used coffee grounds that are processed as general waste, often ending up in landfill or incineration. However, the researchers discovered the coffee grounds can provide both nutrients to feed Chlorella vulgaris microalgae as well as a structure on which it can grow. They were consequently able to extract enhanced biodiesel that produces minimal emissions and good engine performance – meeting both US and European specifications. 

Algae produced by this growing system from Dutch company AlgaeLink is harvested to make ethanol and biodiesel. (Photo by Ashley Cooper via Getty Images)

Algae is typically grown on materials such as polyurethane foam and nylon, which do not provide any nutrients. However, the study found that microalgal cells can grow on the leftover coffee without requiring other external nutrients. The research also indicates that exposing the algae to light for 20 hours a day, and dark for just four hours, creates the highest quality biodiesel.

“This is a breakthrough in the microalgal cultivation system,” Vesna Najdanovic, senior lecturer in chemical engineering at Aston University, said in a statement. “Biodiesel from microalgae attached to spent coffee grounds could be an ideal choice for new feedstock commercialisation, avoiding competition with food crops.

“Furthermore, using this new feedstock could decrease the cutting down of palm trees to extract oil to produce biofuel. In South-East Asia, this has led to continuous deforestation and increased greenhouse gas emissions.”