Can Used Coffee Grounds be Used for Fuel?

Today, coffee is the most-consumed beverage and the second-most-traded commodity, after gasoline. Globally, one ton of green coffee yields six and a half megatons of spent coffee grounds (SCG) annually. SCG can also be used to produce biodiesel, fuel pellets, and fuel for commercial boilers.

The process of torrefaction makes it easy to convert SCG into a high-value fuel product. Biochar production from biomass feedstocks is a sensible strategy for waste management and greenhouse gas mitigation in the fight against climate change. For SCG, whose global production is steadily increasing, the potential use of generated byproducts for the production of high-value-added chemicals or fuels via pyrolysis results in a solution that is both attractive and challenging.

Biomass torrefaction could enable the use of renewable fuels in coal power without the need for new equipment. SCGs have a higher energy content than other biomasses despite having a lower energy potential than fossil fuels. The majority of studies have found that adding biochar improves soil fertility, increases agricultural yields, reduces greenhouse gas emissions, and increases soil carbon stocks.

However, pyrolysis parameters such as feedstock type and temperature influence biochar’s chemical and physical properties. For biochar used in soil applications to be safe, specific requirements must be met. Extensive research has been conducted on SCG and torrefaction; however, no study has examined SCG torrefied on different heat levels for use as a fuel and soil amendment.

About the Research
In this study, the authors conducted an exhaustive, proximate, and stochiometric analysis of torrefied spent coffee grounds. Used coffee grounds were produced from a substance with a high carbon content of over 50% and a high calorific value of more than 20 MJ kg-1. Torrefaction improved the properties of the material, increasing its calorific value to 32 MJ kg-1. The cress test was used to determine the phytotoxicity of the aqueous extract.

The team demonstrated that the non-tortured samples and those heated to 250 degrees Celsius were the most hazardous. Cress seed germination was inhibited by the remaining tannins, caffeine, and sulfur released from the sample heated to 250 degrees Celsius. The sample heated to 350 °C performed the best of those examined. As the germination index was greater than 50%, the sample heated to 350 °C could be used as an alternative fuel with a comparable net calorific value to fossil fuels.

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