Students at the University of Bath have discovered that oil from waste coffee grinds can be used to make biodiesel.

Researchers found that oil can be extracted from coffee grounds by soaking them in an organic solvent, before chemically transforing them into biodiesel via a process called ‘transesterification’.

The study, recently published in the ACS Journal Energy & Fuels, looked at how the fuel properties varied depending on the type of coffee used.

As part of the study, biofuel was made from ground coffee produced in 20 different geographic regions, including caffeinated and decaffeinated forms, as well as Robusta and Arabica varieties.

The research found that there was a reasonably standard composition and little variation in the relevant physical properties of the fuels, irrespective of the source. This means that all waste coffee grounds are a viable feedstock for producing biodiesel.

Dr Chris Chuck, Whorrod Research Fellow from the University’s Centre for Sustainable Chemical Technologies, explained: “Around eight million tonnes of coffee are produced globally each year, and ground waste coffee contains up to 20 per cent oil per unit weight.

“This oil also has similar properties to current feedstocks used to make biofuels. But, while those are cultivated specifically to produce fuel, spent coffee grounds are waste. Using these, there’s a real potential to produce a truly sustainable second-generation biofuel.”

He added: “The yields and properties of biodiesel can differ depending on the growth conditions of current biodiesel feedstocks, sometimes causing them to fall out of specification. The uniformity across the board for the coffee biodiesel fuel is good news for biofuel producers and users.”

“Great potential as a viable fuel source”

The researchers suggest that while coffee biodiesel would be a relatively minor part of the energy mix, it could be produced on a small scale by coffee shop chains to fuel vehicles used for deliveries. These same delivery vehicles could be used to collect spent coffee grinds and take them to a central biodiesel production facility to be processed. Companies such as London-based bio-bean Ltd already produce biodiesel and biomass pellets from waste coffee grounds.

Rhodri Jenkins, a PhD student in Sustainable Chemical Technologies and first author of the study, said: “We estimate that a small coffee shop would produce around 10 kilogrammes of coffee waste per day, which could be used to produce around two litres of biofuel.

“There is also a large amount of waste produced by the coffee bean roasting industry, with defective beans being thrown away. If scaled up, we think coffee biodiesel has great potential as a sustainable fuel source.”

The researchers are also looking at using other types of food waste as a feedstock to make biofuels and expect to publish their findings later in this year.

Biofuels background

Biofuels have been receiving a lot of attention lately, with the European Parliament looking to curb the use of food-based biofuels, which are often criticised for preventing agricultural land from being used to grow food for human consumption, and for potentially high carbon dioxide emissions. Earlier this year, the European Commission (EC) released ‘Guidelines on State aid for environmental protection and energy 2014-2020’, which considered ‘that investment aid in new and existing capacity for food-based biofuel is not justified’. The EC does, however, support ‘advanced’ biofuels, such as those made from waste.

Read more about biofuels in Resource 52, or find out more about the coffee grounds project.