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Coffee grounds — currently wasted or used as garden compost — could become a cheap and environmentally friendly source of biodiesel and fuel pellets, says a study.

Spent coffee grounds contain 11–20 per cent oil, depending on their type. "This is competitive with other major biodiesel feedstocks such as rapeseed oil (37–50 per cent), palm oil (20 per cent), and soybean oil (20 per cent)," say researchers writing in the Journal of Agricultural and Food Chemistry.

Scientists at the US-based University of Nevada, Reno, used an inexpensive process to extract oil from the leftovers of making espressos, cappuccinos and other coffee preparations from a multinational coffeehouse chain.

This oil was then converted into biodiesel, which could be used to fuel cars and trucks.

The world's coffee production is more than 7.2 million tonnes per year, according to US Department of Agriculture figures cited in the study. This could yield about 340 million gallons of biodiesel, say the researchers.

"It is easy and economical to extract oil from used coffee grounds compared to traditional feedstocks," said Mano Misra, an author of the study. Further, coffee oil has some antioxidants which are required for biofuel stability," he told SciDev.Net. After the oil extraction the remaining solid waste from processed coffee can be used as garden compost or fuel pellets.

The process "would be ideal for countries where coffee is produced. A lot of defective coffee beans are discarded into the landfills every year. Processing these beans as well as coffee grounds would be an economical approach," said Misra.

The researchers calculate that in the United States an annual profit of more than US$8 million could be made from biodiesel and pellets from one major coffee chain alone.  

Link to abstract in Journal of Agricultural and Food Chemistry