Researchers Created High-quality Biodiesel by ‘Feeding’ and Growing Microalgae on Used Coffee Grounds

After 'feeding' and growing microalgae on leftover coffee grounds, two Aston University researchers produced high-quality biodiesel.

Dr. Vesna Najdanovic, senior lecturer in chemical engineering, and Dr. Jiawei Wang were members of a team that cultivated algae, which was then processed into fuel.

Every day, approximately 98 million cups of coffee are consumed in the United Kingdom, contributing to a massive amount of spent coffee grounds that are processed as general waste, frequently ending up in landfill or incineration.

Researchers 'feed' leftover coffee grounds to microalgae

(Photo : CHAIDEER MAHYUDDIN/AFP via Getty Images)

However, the researchers discovered that used coffee grounds provide both nutrients and a structure for the microalgae (Chlorella vulgaris sp.) to grow on, as per ScienceDaily.

As a result, they were able to extract enhanced biodiesel with low emissions and good engine performance that meets US and European standards.

The study, "Enhancing growth environment for attached microalgae to populate onto spent coffee grounds in producing biodiesel," will be published in Renewable and Sustainable Energy Reviews in November 2022.

Until now, algae has been grown on non-nutrient-rich materials such as polyurethane foam and nylon.

However, the researchers discovered that microalgal cells can grow on leftover coffee without the need for additional nutrients.

They also discovered that exposing the algae to light for 20 hours per day and darkness for only four hours per day produced the highest quality biodiesel.

"This is a breakthrough in the microalgal cultivation system," said Dr. Najdanovic.

Biodiesel made from microalgae attached to spent coffee grounds could be an excellent choice for new feedstock commercialization because it avoids competition with food crops.

Furthermore, using this new feedstock could reduce the number of palm trees cut down to extract oil for biofuel.

This has resulted in continuous deforestation and increased greenhouse gas emissions in Southeast Asia.

Turning old coffee waste into cleaner biofuels

The cost of purpose-grown feedstocks (used to extract oils) for biodiesels is controversial, as is the demand they place on land and water.

However, spent coffee grounds with a high calorific value make an excellent low-cost alternative feedstock.

However, the majority of used coffee grounds are currently dumped. More than nine million tonnes of spent coffee grounds were disposed of in landfills in 2014.

The chemical engineers have combined the existing multi-stage process (known as in-situ transesterification) into a single step that combines the extraction of oils from spent coffee grounds and the conversion of it into coffee biodiesel.

Traditionally, manufacturers combine spent coffee grounds with hexane and cook the mixture at 60°C for 1-2 hours.

The hexane is then evaporated, leaving the oils behind. Methanol and a catalyst are then added to produce biodiesel and a glycerol by-product, which must also be separated.

Although only a few businesses use spent coffee grounds to make biofuels, researchers at Lancaster University have discovered a way to significantly improve the efficiency of the process, vastly increasing the commercial competitiveness of biofuel from coffee.

Lancaster University researchers led by Dr. Vesna Najdanovic-Visak discovered that they can combine the processes using only methanol and a catalyst, eliminating the need for hexane and reducing chemical waste.

Furthermore, they discovered that the optimal time for the process was 10 minutes in order to obtain the same yield of oils from the spent coffee grounds - a significant reduction in time required and associated energy costs.

According to Dr. Najdanovic-Visak, Lecturer in Lancaster University's Engineering Department, "our method vastly reduces the time and cost required to extract the oils for biofuel, making spent coffee grounds a much more commercially competitive source of fuel."