Researchers have developed a new waste-to-energy technology that converts spent coffee grounds directly into high-value biochar without the need for energy-intensive drying, potentially opening new opportunities for resource recovery from organic waste streams.
The innovation, known as Flame Plasma Pyrolysis (FPP), was developed by researchers at the Korea Institute of Geoscience and Mineral Resources (KIGAM). The process uses atmospheric-pressure plasma generated by the combustion of liquefied petroleum gas (LPG) and compressed air to treat biomass containing around 55% moisture.
Spent coffee grounds are generated in large quantities worldwide, with more than 10 million tonnes produced annually. Most are currently sent to landfill or incinerated, contributing to greenhouse gas emissions and environmental pollution.
A major obstacle to recovering energy from coffee waste has been its high moisture content.
Conventional methods typically require extensive pre-drying before the material can be converted into fuel or carbon products, adding significant energy costs and limiting commercial viability.
The new FPP process eliminates that requirement. Plasma flames operating at temperatures of approximately 800–900°C rapidly heat the wet biomass, causing moisture trapped within particles to vaporise almost instantly. The resulting pressure creates microscopic explosions, described by the researchers as a “popcorn effect”, which enhance carbonisation while producing highly porous carbon structures.
According to the research team, moisture acts not as a barrier but as a steam-activation agent that promotes reactions and improves the quality of the resulting biochar.
Under optimised operating conditions, complete conversion was achieved in just 90 seconds, with a mass reduction of 83.3%.
The resulting biochar demonstrated a heating value of 29.0 MJ/kg, compared with 21.8 MJ/kg for untreated coffee grounds. The figure is comparable to that of anthracite coal, suggesting potential use as a renewable solid fuel.
Researchers also reported a near threefold increase in fixed carbon content, rising from 15.6% to 46.2%, while sulfur compounds were completely removed, preventing sulfur oxide emissions during combustion.
In addition, the specific surface area increased from 1.5 to 115.4 square metres per gram, indicating potential applications as an activated-carbon precursor or adsorption material. The process also generated minimal levels of secondary pollutants such as smoke and tar.
The researchers said the technology offers significant speed advantages over existing biomass treatment methods. Hydrothermal carbonisation can require between one and six hours, while torrefaction generally takes at least 30 minutes. By contrast, the FPP process completes treatment in around 90 seconds.
Because the system uses combustion-generated plasma rather than electricity-intensive plasma devices, the team believes it can achieve lower overall energy consumption while maintaining high processing performance.
Beyond coffee grounds, the technology could be applied to a range of high-moisture waste streams, including food waste, sewage sludge and agricultural residues.
The researchers say the compact design and rapid treatment capability could make the system suitable for decentralised waste-to-energy facilities, where transportation and drying costs often limit the economic recovery of organic waste resources.
