Every year, the dairy and tofu industries generate enormous quantities of protein-rich liquid waste that mostly gets thrown away. Scientists at ETH Zurich have now found a use for it that has nothing to do with food. Researchers led by materials scientist Raffaele Mezzenga extracted proteins from this waste stream, assembled them into tiny porous beads, and loaded them with potassium hydroxide, turning what would have been industrial rubbish into a material that can pull carbon dioxide directly out of the air. In lab tests, one gram of the material captured 97 milligrams of CO2, outperforming conventional direct air capture technologies by 10 to 50 per cent. The findings were published in PNAS on June 8, 2026.
What is Direct Air Capture and why it could be crucial for fighting climate change
Cutting emissions alone will not be enough to keep global warming below 1.5 degrees Celsius. The latest IPCC assessment makes clear that the world will also need to actively remove hundreds of billions of tonnes of CO2 already sitting in the atmosphere. Direct air capture, or DAC, is one of the main technologies being developed to do this. It works by pulling air through a material that binds carbon dioxide, then releasing the CO2 in a concentrated form that can be stored underground or converted into other products.The problem is cost and energy. Most existing DAC systems require significant heat to release captured CO2 from the sorbent material, which makes the whole process expensive and energy-intensive. Several companies, including Climeworks, an ETH Zurich spin-off, have been running commercial DAC plants for years, but the cost per tonne of CO2 removed remains high enough to limit how widely the technology can be deployed.
How ETH Zurich researchers turned food industry waste into a carbon capture sorbent
The ETH Zurich team approached the problem from an entirely different angle. Rather than engineering a synthetic material from scratch, they started with something the food industry was already discarding. During the production of dairy products like yoghurt and cheese, and during the making of tofu, large volumes of protein-rich liquid are generated. Most of it ends up as waste.Mezzenga’s group extracted proteins from this liquid and assembled them into long, thread-like structures called amyloid fibrils. These fibrils were then combined with potassium hydroxide and shaped into small porous beads, roughly half a centimetre to one centimetre in diameter. The beads look unremarkable, but their internal structure is highly porous, giving them a large surface area to interact with air.“The resulting material is like a sponge that can absorb large quantities of CO2 via the potassium hydroxide,” Mezzenga explains. When air passes over the beads, the potassium hydroxide reacts with CO2 and converts it into hydrogen carbonate, effectively locking the carbon into a salt form inside the bead.
How the new carbon capture beads perform compared to conventional DAC technology
In tests using real ambient air, the beads captured 97 milligrams of CO2 per gram of material. Based on the team’s calculations, one kilogram of beads could theoretically capture 100 grams of CO2 in a single operating cycle. That figure places the material well above what most conventional DAC sorbents achieve.What makes the release process particularly notable is that it requires no heat at all. Most existing systems heat the sorbent to temperatures of 80 to 120 degrees Celsius to drive off the captured CO2, a step that accounts for a large share of the energy cost. The ETH Zurich approach instead sprays the beads alternately with a mild acid and a mild base for around ten minutes at room temperature. This breaks the chemical bonds holding the CO2 without any thermal input, and both the acid and base can be recovered and reused in the next cycle.Laboratory tests showed the beads maintained their performance through 30 capture and release cycles with no significant drop in efficiency. Mezzenga expects they would eventually need replacing after several thousand cycles, but even then they would not simply be discarded.
Why the used carbon capture beads can still be turned into fertiliser or biofuel
One of the more unusual aspects of this technology is what happens to the beads at the end of their useful life for carbon capture. Because the material is entirely organic and food-grade, spent beads could be applied directly to agricultural soil as a fertiliser, contributing nutrients that support crop growth. Alternatively, they could be processed into biofuel.This end-of-life flexibility is what allows the researchers to describe the system as genuinely circular. The input is food industry waste. The output is captured carbon. And when the capture material is exhausted, it feeds back into either the food system or the energy system rather than becoming a new waste problem.A life cycle analysis conducted by the team confirmed that the full environmental footprint of the new method is lower than that of existing DAC approaches, taking into account both the production of the sorbent material and the energy used during operation.
What needs to happen before food waste carbon capture can scale up
The current study tested only a few grams of material under controlled laboratory conditions, capturing roughly 50 grams of CO2 in total. Moving from that scale to something industrially meaningful is a significant engineering challenge, and Mezzenga is candid that more research is needed before anyone can say with certainty that the performance holds at larger scales.That said, the spray-based acid and base release system is not novel technology. Industrial processes already use similar spray systems widely, which means the infrastructure for scaling it up is not being invented from scratch. Lead author Zhou Dong’s next research work will focus specifically on evaluating how the system performs at larger scale.The cost per tonne of CO2 removed has not yet been calculated precisely, but Mezzenga expects it to come in considerably below current DAC costs, primarily because the sorbent material starts as waste rather than a manufactured input, and because the energy-intensive heating step has been removed entirely.“Our technology is cheaper and more sustainable because it requires little energy and is based on a widely available waste product,” he says. “That could be a game changer for the future of removing CO2 from the air.”
