16.12.2025 | Kompogas Winterthur AG and Swiss climate-tech pioneer neustark have put a pioneering plant into operation
Binding CO2 in concrete instead of releasing it into the atmosphere
A pioneering project in Winterthur shows how the circular economy can contribute to climate protection. Kompogas Winterthur AG - a joint venture between Axpo Biomass and the cities of Winterthur and Frauenfeld - and the climate tech start-up neustark have recently started operating the city's first active CO₂ sink. It captures biogenic CO₂, liquefies it on site and ensures that it is permanently stored in mineral building materials.
Every day, fully loaded lorries bring green waste to the Kompogas Winterthur AG fermentation plant. But since autumn 2024, there have also been lorries leaving the fermentation plant fully loaded. They transport an unusual cargo, namely liquefied CO2. "After a test phase lasting several months, the new CO2 liquefaction plant is now in operation," says Daniel Ribi, Operations Manager at Axpo Biomasse. This has enabled a so-called CO2 sink to be realised in Winterthur, an important step on the way to net zero.
Up to 1600 tonnes per year possible
Kompogas Winterthur AG's fermentation plant produces biogas from around 20,000 tonnes of green waste per year. This also produces around 1,600 tonnes of biogenic CO₂. Thanks to the new plant, this greenhouse gas is no longer released into the atmosphere, but is instead liquefied and delivered to building material recycling companies in the region. There it is incorporated into demolition concrete: A mineralisation process accelerated by new technology ensures that the CO₂ remains stable in the rock for hundreds of thousands of years.
For Axpo, the project is far more than a symbolic contribution. The company is gaining valuable operating experience here and will consider equipping more of its own 15 fermentation plants with CO₂ liquefaction. The collaboration demonstrates how energy suppliers, cities and start-ups can work together to take concrete steps towards the Swiss climate target of "net zero 2050".
The plant has been in regular operation since receiving its official certificate of conformity. The first load of liquefied CO₂ left Winterthur on 29 October 2024. Since then, 60 loads have already been carried out by the end of November 2025 - with a total of 923 tonnes of CO₂ permanently removed from the cycle. A clear indication of the potential of this technology.
How the CO2 sink works in Winterthur
After liquefaction, the CO2 is transported to companies that recycle building materials and reprocess recyclable materials, where neustark's technology is used. This integrates seamlessly into the recycling companies' existing processes. The CO2 is injected into the granulate of demolition concrete as an additive to the existing recycling process. This triggers an accelerated mineralisation process and permanently binds the CO2 to the pores and surface of the granulate. The carbonised granulate can then be used for road construction or for the production of recycled concrete. Carbon Dioxide Removal (CDR) from neustark is measurable, verified by Gold Standard and permanent. The mineralisation process stores the captured CO₂ for hundreds of thousands of years and the risk of a relapse is demonstrably low to non-existent.
neustark
The Swiss company neustark is a leading provider in the fast-growing field of Carbon Dioxide Removal (CDR) and has developed a solution for the permanent storage of biogenic CO₂ in recycled mineral waste such as demolition concrete. neustark AG was founded in July 2019 by Valentin Gutknecht and Johannes Tiefenthaler and is based in Bern. There are currently 44 CO2 capture and storage plants in operation in eight European countries.
Kompogas Winterthur AG
Kompogas Winterthur AG is a joint venture between Axpo Biomasse AG and the cities of Winterthur and Frauenfeld, represented by Stadtwerk Winterthur and Thurplus. The company has been operating the fermentation plant in Winterthur for around eleven years. It processes around 20,000 tonnes of green waste from Winterthur, Frauenfeld and the surrounding municipalities every year and produces biogas from it. Axpo Biomasse AG is the largest shareholder with a 52 per cent stake. The city of Winterthur has a 34 per cent stake and Frauenfeld holds 14 per cent. The operation of the plant is in the hands of Axpo Biomasse AG.
