The world drinks 2.25 billion cups of coffee daily. The roughly 10 million tons of wet coffee grounds produced end up almost entirely in landfills, where the material decomposes under oxygen-free conditions to release methane, a particularly potent greenhouse gas. Researchers at South Korea's Korea Institute of Geoscience and Mineral Resources (KIGAM) have now succeeded in converting this waste into high-grade solid fuel in less than 90 seconds, without requiring the wet material to be pre-dried.
Coffee Waste as an Overlooked Disposal Problem
For the coffee and food industries, coffee grounds present a stubborn logistics challenge. The material contains approximately 55 percent moisture: too wet for direct thermal processing, too energy-rich for simple landfill disposal. The most obvious alternative, conventional pyrolysis, has failed economically so far: converting wet coffee grounds into biochar requires drying it first, which consumes significant energy and burdens the process's carbon footprint.
Hydrothermal carbonization (HTC), another established approach, requires between one and six hours for conversion depending on the facility and requires pressure vessels. This limits industrial deployment. The result: most coffee grounds still end up in the trash.
How Flame Plasma Turns Moisture Into an Asset
Dr. Taejun Park and his team at KIGAM have published a new approach with Flame Plasma Pyrolysis (FPP) that transforms the moisture problem into an advantage. The process burns liquefied petroleum gas (LPG) together with compressed air into an atmospheric plasma at temperatures of 800 to 900 degrees Celsius. When this flame jet strikes wet coffee grounds, the contained moisture evaporates instantly. The researchers call this the popcorn effect: the explosive evaporation tears apart the particle structure and simultaneously creates a highly porous surface in the resulting biochar, which is important for later applications as a soil amendment or activated carbon precursor.
The results, published by the team in the Chemical Engineering Journal, are precisely documented. After 90 seconds, conversion is complete. The biochar's heating value is 29.0 megajoules per kilogram, equivalent to anthracite coal and 33 percent higher than the starting material (21.8 MJ/kg). Carbon content increases from 15.6 to 46.2 percent, and specific surface area grows from 1.5 to 115.4 square meters per gram. Sulfur is completely eliminated, improving air quality during later combustion. Compared to hydrothermal carbonization, the process is between 40 and 240 times faster.
Another advantage: the flame plasma forms through combustion, not energy-intensive plasma generators. This significantly reduces investment costs for industrial facilities.
What Biochar Can Do: A Comparison
Biochar is not a new material. Pre-industrial inhabitants of the Amazon region improved their soils with charred biomass, known as Terra Preta (black earth). These soils remain, even after more than 1,000 years, more fertile than surrounding soils. They contain three to five times more organic carbon than neighboring soils without biochar treatment. The carbon remains permanently bound, rather than entering the atmosphere as CO2.
Rice husks offer another benchmark. Globally, approximately 150 million tons are produced annually. More than 90 percent are currently burned openly or disposed of in waterways. Pyrolysis facilities in parts of Asia already convert rice husks into biochar. The KIGAM team states that the FPP process is also suitable for these and other wet waste streams.
A study in the journal Communications Earth and Environment (2025) quantifies biochar's global climate protection potential at 0.5 to 2 billion tons of CO2 equivalents per year. For comparison, all forests on Earth bind a net average of 7.6 billion tons of CO2 annually, according to World Resources Institute calculations. Biochar could thereby complement a significant portion of this natural carbon sink.
Until Coffee Cafeterias Become Biochar Producers
The KIGAM process has been tested so far only at laboratory scale. For broad deployment, several conditions must align.
First, energy balance: the flame plasma process burns LPG. Whether the recovered biochar yields more energy than the LPG investment costs depends on specific system design and the biochar's intended use. If the biochar is burned for energy, the balance differs from soil improvement, where carbon remains permanently bound.
Second, logistics: coffee grounds arise distributed across households, cafes, cafeterias, and industrial roasteries. Large roasteries and food companies with in-house coffee waste would be the obvious early adopters, since the material accumulates in one location. For widespread deployment, collection infrastructure is needed to consolidate many small sources.
Third, sales markets: biochar as a soil amendment is well documented, but the market remains fragmented. As a fuel or activated carbon precursor, demand exists, though reliable pricing structures are still developing. GodTech Co. Ltd., the company that supported the researchers in the study, is reportedly working to scale the process to other wet organic waste streams, including sewage sludge and other food waste. Whether this becomes a viable industrial application depends on how quickly collection infrastructure and biochar demand grow in parallel.