Wet coffee grounds turned into high-grade solid fuel in just 90 seconds - Engineering - Energy & Green Tech

Atmospheric-pressure flame plasma system. Credit: Chemical Engineering Journal (2026). DOI: 10.1016/j.cej.2026.176452

A research team at the Korea Institute of Geoscience and Mineral Resources (KIGAM) has developed a technology that converts wet spent coffee grounds directly into high-quality biochar in just 90 seconds, with no drying or oil removal required. The breakthrough offers a fast, energy-efficient path to turning high-moisture organic waste into valuable fuel and carbon materials. The study, led by Dr. Taejun Park in collaboration with GodTech Co., Ltd., was published in the Chemical Engineering Journal, one of the world's leading journals in chemical engineering.

Addressing a growing waste challenge

Every year, global coffee consumption generates more than 10 million tons of spent coffee grounds, most of which end up in landfills or are incinerated, releasing greenhouse gases and polluting the environment.

Spent coffee grounds hold real energy potential, but their high moisture content has long been a barrier. Converting them into fuel or carbon products typically requires energy-intensive predrying, making large-scale resource recovery economically impractical.

World-first flame plasma pyrolysis technology

To overcome this challenge, the KIGAM team developed Flame Plasma Pyrolysis (FPP), a process that directly treats biomass containing approximately 55% moisture under atmospheric-pressure plasma conditions.

The system generates plasma flames at temperatures of approximately 800–900°C (1,472–1,652°F) through the combustion of liquefied petroleum gas (LPG) and compressed air. Unlike conventional pyrolysis technologies, the process eliminates the need for any predrying treatment.

During processing, the intense thermal energy rapidly vaporizes moisture trapped inside the biomass particles. The resulting pressure buildup triggers microscopic explosions known as the "popcorn effect," which simultaneously enhance carbonization and create highly porous structures. Rather than acting as a barrier, moisture itself becomes a steam-activation agent that accelerates reactions and improves product quality.

The process proceeding in a clean manner, with almost no smoke or oil observed during treatment. Credit: Korea Institute of Geoscience and Mineral Resources(KIGAM)

Anthracite-level fuel performance

Under optimized conditions, the researchers achieved complete conversion within 90 seconds, with a mass reduction of 83.3%.

The resulting biochar exhibited a heating value of 29.0 MJ/kg, approximately 33% higher than the original coffee grounds (21.8 MJ/kg) and comparable to that of anthracite coal.

Additional performance improvements included:

• a nearly threefold increase in fixed carbon content (from 15.6% to 46.2%)
• complete removal of sulfur compounds, preventing sulfur oxide (SOx) emissions during combustion
• an increase in specific surface area from 1.5 to 115.4 m²/g, indicating potential use as an activated carbon precursor or adsorption material
• minimal formation of secondary pollutants such as smoke and tar

These characteristics make the biochar suitable not only as a renewable solid fuel but also as a high-value carbon material for environmental and industrial applications.

(a) SEM images at different exposure times. (b) Schematic illustrating the transformation from non-porous raw SCG to peak porosity and eventual collapse with extended treatment. Credit: Korea Institute of Geoscience and Mineral Resources(KIGAM)

Dramatically faster than existing technologies

The new process offers substantial advantages in both processing speed and energy efficiency.

Compared with hydrothermal carbonization (HTC), which typically requires one to six hours, the FPP process is 40 to 240 times faster. It also reduces treatment time by more than 20-fold compared with torrefaction, which generally requires at least 30 minutes.

Because the system relies on combustion-generated plasma rather than electricity-intensive plasma devices, it lowers overall energy consumption while maintaining high processing performance.

The researchers emphasize that the ability to directly process wet feedstocks without predrying represents one of the technology's most significant economic and environmental advantages.

Potential for distributed waste-to-energy systems

Beyond coffee waste, the technology could potentially be applied to a wide range of high-moisture organic wastes, including food waste, sewage sludge and agricultural residues.

Its compact process design and ultrafast treatment capability make it particularly attractive for decentralized, onsite waste-to-energy facilities, where transportation and drying costs often limit resource recovery efforts.

The study demonstrates a new approach for transforming wet organic waste into valuable energy resources while advancing carbon-neutral waste management strategies.

"This technology presents a new paradigm in which waste is no longer viewed as a disposal problem but as a valuable energy resource," said Park. "We plan to expand the technology to various types of high-moisture organic waste and further optimize the process for industrial-scale commercialization." 

Provided by National Research Council of Science and Technology 

by National Research Council of Science and Technology

edited by Gaby Clark, reviewed by Robert Egan 

Source: Wet coffee grounds turned into high-grade solid fuel in just 90 seconds