Waste from Cheese and Tofu Production Could Be a Cheap Solution for Absorbing Carbon Dioxide

Reducing greenhouse gas emissions alone is no longer considered sufficient to curb global warming. Scientists agree that some of the carbon already trapped in the atmosphere must be drawn back and stored permanently. One method used is direct air capture technology, but this approach is notoriously expensive and energy-intensive. Now, a group of material scientists in Switzerland have discovered an innovative solution that is far cheaper and more environmentally friendly. Remarkably, the solution utilises food industry waste that is usually discarded: the liquid residue from cheese and tofu production. Raffaele Mezzenga, a material scientist from the Swiss Federal Institute of Technology in Zurich (ETH Zurich), has dedicated his career to transforming protein waste into useful materials. The research team extracted protein from the liquid waste of dairy and tofu factories, then assembled it into long, fine strands called amyloid fibrils. These fibres were subsequently coated with potassium hydroxide, a caustic chemical, and pressed into small porous granules measuring less than half an inch. When the protein granules are placed in open air, a chemical reaction occurs. The potassium hydroxide inside the granules reacts with passing carbon dioxide (CO2), binding the gas into a stable solid substance similar to baking soda within its pores. In laboratory-scale trials using ordinary room air, one gram of this material was able to capture approximately 97 milligrams of carbon dioxide. This figure surpasses the capacity of many conventional materials by 10 to 50 percent. By calculation, one kilogram of the granules can trap around 100 grams of CO2 in each phase. The main advantage of this innovation lies in its carbon release process, which does not require high heat energy or electricity-guzzling vacuum pumps. To release the trapped carbon load for permanent storage, the granules simply need to be sprayed with a mild acidic liquid followed by a mild alkaline liquid for 10 minutes at room temperature. The chemicals used for spraying, as well as the protein granules themselves, can be reused repeatedly. In testing, the protein granules proved highly stable and capable of withstanding up to 30 capture and release cycles without losing their absorption capacity. “On the contrary, our protein granules remain stable for a long time,” said Zhou Dong, a postdoctoral researcher in Mezzenga’s laboratory and the lead author of the study. After thousands of cycles when they can no longer be used, the food-safe organic granules can be composted into fertiliser or converted into biofuel. Although trials have so far only been conducted on a small scale in the laboratory testing a few grams of granules, the research team is optimistic the technology can be applied on an industrial scale. Given that food waste accounts for 8 to 10 percent of global greenhouse gas emissions, utilising this cheap waste offers a much smaller carbon footprint compared to competing technologies. “Our technology is cheaper and more sustainable because it requires little energy,” said Mezzenga, who also noted that the waste raw material they use is available almost worldwide. The promising study has been officially published in the scientific journal PNAS.