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Researchers at ETH Zurich are testing a new use for protein-rich liquid residuals from dairy and tofu manufacturing, turning them into porous beads that can capture carbon dioxide from the air. The study adds to a growing body of work looking at clean food processing byproducts not as waste, but as raw materials for higher-value climate applications.
The study, published in the Proceedings of the National Academy of Sciences, describes a direct air capture material made from amyloid fibrils, which are long, thread-like protein structures assembled from liquid waste streams generated during dairy and tofu production. The fibrils are combined with potassium hydroxide and formed into porous beads roughly half a centimeter to one centimeter in diameter. When exposed to air, the potassium hydroxide inside the beads reacts with carbon dioxide and converts it into hydrogen carbonate, removing CO₂ from the atmosphere.
The work is still at laboratory scale, but the performance numbers are notable. In tests with ambient air, the material captured 97 milligrams of CO₂ per gram of material. The researchers reported that one kilogram of the protein beads could theoretically capture and isolate about 100 grams of CO₂ in a single operating cycle, which they described as 10% to 50% higher than conventional direct air capture materials.
The energy requirement is the other factor where the study is drawing attention. Many direct air capture systems use heat and negative pressure to release captured CO₂ from sorbent materials so it can be stored or converted into other products. That regeneration step is one reason direct air capture remains costly and is most practical where low-carbon energy is abundant. In the ETH Zurich system, captured CO₂ is released by spraying the beads with a mild acid and a mild base for about 10 minutes at room temperature. The acid, base and beads can be reused afterward.
“The resulting material is like a sponge that can absorb large quantities of CO₂ via the potassium hydroxide,” Raffaele Mezzenga, the ETH Zurich materials scientist who led the research team, said in a university summary of the work. Zhou Dong, a postdoctoral researcher in Mezzenga’s group and lead author of the study, added that the beads remained stable in laboratory testing, maintaining performance through 30 capture and release cycles without a significant decline in efficiency.
For the composting and organics recycling sector, the most relevant part of the study may not be direct air capture itself. It is the material pathway. The researchers used protein-rich liquid residuals from food manufacturing, streams that are generated in large quantities and often have limited higher-value outlets. By extracting proteins and using them as a structural platform for carbon capture, the study places food processing byproducts in the same conversation as renewable energy, bioproducts and advanced circular economy materials.
That is a different frame than conventional food waste management, where the first question is usually whether the material should be fed, digested, composted or disposed. This research asks whether some food processing residuals have molecular properties that make them useful before they enter bulk organics management systems. The answer will not apply to all food waste streams, especially mixed postconsumer food scraps with contamination and variable composition. It may, however, apply to relatively clean, industrial residuals that are already generated at scale and can be aggregated with predictable quality.
The researchers also looked at end-of-life pathways for the beads. Because the material is organic and biodegradable, the team suggests that used beads could eventually be applied as fertilizer or converted into biofuel after their carbon capture performance declines. That remains conceptual, and the presence of potassium hydroxide and the chemistry of repeated acid and base treatments would need careful evaluation before any agricultural use. Still, the circular economy premise is clear. The material begins as a food manufacturing byproduct, performs a carbon capture function, and may retain enough biological value to avoid becoming another waste stream.
The scale question remains large. The ETH Zurich team tested only a few grams of material under controlled laboratory conditions and captured roughly 50 grams of CO₂. The researchers have not yet calculated the cost per ton of CO₂ removed, and future work will need to determine whether the beads can perform consistently in larger systems exposed to real-world air flows, humidity, impurities and repeated regeneration.
The study makes a case for broadening the value proposition for food waste. Composting and anaerobic digestion will remain essential outlets for organic materials, particularly mixed streams and materials with clear soil or energy value. But clean industrial residuals may increasingly be pulled into new markets for carbon management, biobased materials and climate technology. If those pathways scale, the organics sector will need to understand not only how much residual material is available, but which fractions are best suited for soil, energy, animal feed or higher-value carbon applications.
