Spent Coffee Grounds and Empty Bottles Used to Make Carbon Filter

Coffee waste from Starbucks in Dubai, UAE, co-pyrolyzed with PET plastics to produce activated carbon for CO₂ capture. Credit: Haif Aljomard.

Two common waste materials — spent coffee grounds and plastic water bottles — may be transformed into material that captures carbon dioxide from industrial emissions. 

In August, researchers affiliated with the University of Sharjah in the UAE received a U.S. patent for a method involving “co-pyrolysis” that heats a mixture of spent coffee grounds, polyethylene terephthalate (PET) plastic and potassium hydroxide to create activated carbon. 

The porous carbon material could then be used as a plug-and-play solution for existing industrial filtration systems, the university suggested late last year. 

On its surface, the innovation addresses two waste streams simultaneously. Credible estimates based on global coffee consumption suggest there is somewhere between 6-8 million metric tons of coffee annually in the waste stream. Meanwhile, PET plastic — a popular material for plastic bottles and food packaging — adds approximately 35 million metric tons to the annual waste stream. 

The inventors of the new technology suggest some portion of this waste could be transformed for use on an industrial scale. 

“What begins with a Starbucks coffee cup and a discarded plastic water bottle can become a powerful tool in the fight against climate change through the production of activated carbon,” said lead inventor Haif Aljomard.

According to the inventors, the relatively low heating activation temperature in the process — about 600°C — allows for relatively eco-friendly production, resulting in a porous, charcoal-like carbon material packed with tiny cavities where gas molecules and impurities can stick.

“This invention repurposes two abundant waste streams — coffee and plastic — into a high-performance adsorbent,” Aljomard said. “The resulting activated carbon shows strong potential for capturing CO₂ from fossil fuel-based energy systems, contributing to the reduction of air pollution.”

Because this is a patent, not an open-access publication, the technology is proprietary. Any commercial rollout would likely run through university licensing or ventures. All four named inventors — Haif Aljomard, Abrar Inayat, Rafik Kalfat and Chaouki Ghenai — are affiliated with the University of Sharjah, which holds the IP.

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