Used coffee grounds can already be turned into things such as water filters, road material, carbon-capture media, and biofuel. Unfortunately in the case of the latter, it's a fairly complex affair, making its widespread use unlikely. That could be about to change, however, as scientists from Britain's Lancaster University have simplified the coffee-grounds-to-biofuel conversion process.

First of all, the vast majority of used coffee grounds are still just thrown away.

Of those that are converted into biofuel, though, the process typically starts with the grounds being mixed with hexane and then heated to 60 ºC (140 ºF) for one to two hours, to extract oils from them. Next, the hexane is evaporated, leaving the oils behind. Methanol and a catalyst are then added to create biodiesel, although glycerol is also created as a by-product. In a final step, it must be separated from the biodiesel.

Led by Dr. Vesna Najdanovic-Visak, the Lancaster team developed a proprietary technique known as in-situ transesterification, which combines the oil extraction and oil-to-biodiesel stages in a single step. The hexane is left out altogether, with the methanol and a different concentration of the catalyst (sodium hydroxide) being added directly to the grounds. Additionally, extraction of oil from the grounds takes only 10 minutes, as opposed to an hour or two.

"Our method vastly reduces the time and cost needed to extract the oils for biofuel making spent coffee grounds a much more commercially competitive source of fuel," says Najdanovic-Visak. "A huge amount of spent coffee grounds, which are currently just being dumped in the landfill, could now be used to bring significant environmental benefits over diesel from fossil fuel sources."

A paper on the research was recently published in the Journal of Environmental Chemical Engineering.