Behind every cup of coffee, leftover grounds often end up in the trash. However, did you know that coffee grounds, also known as spent coffee grounds (SCG), can be used as a renewable energy source? A recent study reveals an innovative method that can convert SCG into biodiesel, offering an eco-friendly solution while reducing waste and creating renewable energy.

Starting from the increasing demand for renewable energy, a creative idea emerged from Chemist at the Universitas Sumatera Utara Indonesia, Prof. Juliati Br. Tarigan. Non-renewable fossil fuel reserves are being depleted, and environmental concerns are also increasing. Meanwhile, coffee consumption continues to grow, increasing the amount of coffee grounds produced. According to Tarigan, these grounds can be processed into a valuable energy source rather than thrown away.

“SCG requires waste treatment before disposal because it contains acids that can pollute the environment. In addition, the amount of SCG continues to increase every year because coffee is a favorite drink in the world, with a consumption of 9.5 million tons in 2016, including instant coffee, where every gram of coffee can produce 0.65-0.91 grams of SCG,” explained Prof. Juliati Br. Tarigan.

Together with Mimpin Ginting, Firman Sebayang, Eko K. Sitepu, Junedi Ginting (University of North Sumatra Indonesia), Siti Nurul Mubarokah (Islamic University of Malang), Justaman Karo-Karo (Ministry of Industry of the Republic of Indonesia), and Trung T. Nguyen (Giang University, Vietnam), this research proposes biodiesel as one of the solutions that can be used directly in diesel engines without the need for modification. However, the main challenge in biodiesel production is the high processing cost.

Their research proved that wet coffee grounds can be converted directly into biodiesel through an efficient and environmentally friendly process using the in situ transesterification method. This process involves the chemical reaction of fatty acids being converted into fatty acid methyl esters (FAME), the main component of biodiesel. The process is carefully monitored using spectroscopic techniques such as FT-IR and 1H-NMR, ensuring efficient conversion and high product quality.

Lipid extraction in a Reactive Extraction Soxhlet (RES) produces biodiesel from wet SCG biomass. RES enables efficient oil extraction from coffee grounds, even under moist conditions, which is usually a challenge in traditional extraction processes. The use of time and energy in the RES method was lower than the two-stage method (separate extraction and transesterification). The resulting SCG contains about 12% oil in its dry matter form.

“The RES method is more energy efficient, but also time efficient, as it does not require the conventional drying process that takes three days in the sun and one night using a hot air oven at 105°C,” said Prof. Juliati Br. Tarigan.

In a minimum reaction time of 30 minutes, they found that the transesterification process successfully converted the fatty acids in SCG into biodiesel efficiently. The dominance of palmitic acid and linoleic acid in the fatty acid profile of SCG makes it very suitable for biodiesel production, as these two fatty acids produce stable and fuel-efficient FAME.

According to Prof. Juliati Br. Tarigan, converting coffee grounds into biodiesel offers a solution to the abundant coffee waste and contributes to reducing carbon emissions and dependence on fossil fuels. “This is an important step towards a circular economy, where waste is converted into useful products, significantly reducing environmental impact,” she continued.

This innovation brings great hope. The journey of coffee grounds to biodiesel proves that a cup of coffee can be utilized as a clean alternative fuel. As awareness of environmental and sustainability issues increases, innovations like this will be increasingly important in creating a greener future.