Recycling Spent Coffee Grounds into Green Energy

Qin Xiang Ng


Category: Diversifying our energy mix
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Biodiesel is a form of diesel fuel manufactured from vegetable oils, animal fats, or recycled restaurant greases. It is environmentally-friendly, safe, biodegradable, and produces less air pollutants than petroleum-based diesel, making it a good alternative for fossil fuel. However, biodiesel is currently more expensive than fossil fuels, limiting its applications. The major production cost of biodiesel is from its feedstock.


The primary problem that the biodiesel industry faces today is the availability of low-cost and good quality feedstock.


To meet this challenge, spent coffee grounds, a ubiquitous waste material, could be tapped into as a potential source for the production of biodiesel as well as fuel pellets. Coffee is one of the most popular beverages in the world. According to the U.S. Department of Agriculture, the world’s coffee production is 16.34 billion pounds per year. Large amounts of spent coffee grounds are produced as a result of the brewing process.


These spent coffee grounds have no commercial value and are currently disposed of as a solid waste or, in some cases, used as fertilizers or burned. Due to their high organic material content and the presence of compounds such as caffeine, tannins, and polyphenols, which can have negative effects on the environment and result in the release of greenhouse gases into the atmosphere, the disposal of these spent coffee grounds should be properly managed. It is known that, on average, spent coffee grounds contain around 15% oil.


Since oil is insoluble in water, it is possible to extract the coffee oil from these solid residues using non-polar solvents (e.g. hexane and ether). The oil extracted can be further made into biodiesel using transesterification methods. The biodiesel extracted from coffee possesses better stability than biodiesel from other sources due to its high antioxidant content, which hinders the rancimat process. Recycling spent coffee grounds into biodiesel is economical, eco-friendly, and can potentially contribute 340 million gallons of biodiesel to the world’s fuel supply, helping to meet the growing energy needs of an expanding and wealthier population.

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