Scientists Turn Wet Coffee Grounds Into Coal-Like Fuel in Just 90 Seconds

A new process skips energy-intensive drying for recycling coffee waste.

Each year, the world discards more than 10 million tons of spent coffee grounds, and most go to landfills or incinerators, even though they still contain usable energy.

Now, researchers in South Korea have found a way to transform those soggy leftovers into high-quality biochar—a carbon-rich solid fuel—in just 90 seconds. The technique works without drying the coffee grounds first, overcoming one of the biggest obstacles that has long made recycling this waste expensive and energy-intensive.

Turning Spent Coffee Moisture into an Advantage

Most methods for turning coffee waste into fuel first dry the grounds, which usually contain about 55% moisture. That drying step consumes large amounts of energy; so much so that the energy you get back as solid fuel often isn’t worth the squeeze.

The research team at the Korea Institute of Geoscience and Mineral Resources (KIGAM), working with GodTech Co., Ltd., instead developed a process called Flame Plasma Pyrolysis (FPP). The system generates a plasma flame at roughly 800–900°C using liquefied petroleum gas (LPG) and compressed air rather than electricity-intensive plasma devices.

With exposure to intense heat, the water trapped inside the coffee grounds rapidly turns to steam. Pressure builds until microscopic “popcorn” explosions rupture the particles, creating a network of pores while accelerating carbonization. Instead of slowing the process, the moisture helps activate it.

The researchers report that the treatment produces almost no smoke or bio-oil, unlike many conventional pyrolysis methods.

Comparable to Anthracite

Under the optimal treatment time of 90 seconds, the process reduced the material’s mass by 83.3% and produced biochar with a heating value of 29.0 megajoules per kilogram—about 33% higher than untreated coffee grounds and comparable to anthracite coal.

The biochar’s fixed carbon content nearly tripled, rising from 15.6% to 46.2%. The process also completely removed sulfur from the mix, meaning the fuel would not produce sulfur oxide emissions during combustion. Sulfur in fuels can form sulfur oxides, or SOx, which contribute to air pollution, acid rain, respiratory irritation, and corrosion in boilers or exhaust systems. Removing sulfur also reduces the need for extra pollution-control equipment.

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At the same time, the material’s surface area increased from 1.5 to 115.4 square meters per gram, making it a potential starting material for activated carbon and industrial adsorbents.

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The study also found that extending the treatment beyond 90 seconds reduced fuel quality as excessive heating began to damage the carbon structure.

No More Pre-Drying

The researchers say the new process dramatically shortens production times. Hydrothermal carbonization, another technique for processing wet biomass, typically requires one to six hours. Torrefaction generally takes at least 30 minutes. By comparison, Flame Plasma Pyrolysis completes the conversion in just a minute and a half.

Because the system eliminates the need for pre-drying and uses combustion-generated plasma, it could also lower overall energy consumption while simplifying operations.

The team believes the approach could eventually be used for other wet organic wastes, including food waste, sewage sludge, and agricultural residues. Its compact design could make it suitable for decentralized waste-to-energy facilities located close to where waste is generated, reducing transportation and processing costs.

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

The study was published in the Chemical Engineering Journal.