The city cannot achieve its climate goals through savings alone. That is why it is now planning an expensive pioneering project, which will be voted on on September 22nd.
CO2 from the city of Zurich will one day be stored in the seabed of the Danish North Sea.
Christoph Wagner / Getty
The idea sounds futuristic, but its implementation is close: In the future, the city of Zurich wants to extract CO2 that is produced when sewage sludge is burned, liquefy it and dump it in the Danish North Sea. There, 2000 meters below the seabed, it will be stored permanently – and help Zurich to improve its carbon footprint.
The city wants to be climate neutral by 2040. Fossil fuels are to be replaced with environmentally friendly alternatives, drivers are to switch to public transport more often, and buildings are to be renovated sustainably. And because in the eyes of the red-green government, every ton of CO2 saved counts, the city also practices micromanagement – for example, by encouraging restaurants to be more sustainable with a charter.
The only problem is that the net zero target cannot be achieved with restrictions and savings alone. In certain areas of life, CO2 emissions are unavoidable, such as in nutrition, waste disposal or sewage treatment plants. That is why the city is relying on so-called negative emissions that can be attributed to the climate balance: CO2 is removed from the atmosphere and stored permanently.
On September 22, voters in the city of Zurich will decide on the construction of a plant to capture CO2 in the largest sewage treatment plant in Switzerland. It is scheduled to go into operation in 2028. The city calls it a pioneering project.
Today, the Werdhölzli site not only treats the city’s wastewater, but also processes all the sewage sludge from the canton of Zurich and several other cantons. Around 100,000 tons of sewage sludge remain each year and are incinerated. This produces flue gas and 20,000 tons of CO2.
Until now, this was blown into the air. In future, it will be separated from the flue gas and liquefied. At a later date, around 5,000 tonnes of CO2 emissions from the biogas processing plant will be added. In total, around 25,000 tonnes of CO2 could be separated in this way.
Half of this will be permanently bound in recycled concrete from various Swiss concrete plants. The other half will be transported to a storage site abroad, probably in the Danish North Sea, with the help of Project “Greensand” – a consortium of 23 international companies.
The CO2 is to be injected under a layer of capstone 2,000 meters below the seabed. According to the Zurich City Council, a geological CO2 storage license from the Danish government has been issued for the offshore transport and storage project.
One thing is clear: the amount of CO2 that can be captured using this method is minimal. For comparison: According to the Federal Office for the Environment, Switzerland produces 41.6 million tonnes of greenhouse gases per year. So how useful is the project in Zurich?
Finding know-how is difficult
Cyril Brunner is a climate researcher at the Department of Environmental Systems Science at ETH Zurich. He says: “Without CO2 capture, we will not achieve the net zero target.” It is a technology that has been used for decades; in industry, in natural gas production, in biogas plants. The transport and storage of CO2 is also a proven method, says Brunner.
The capture of CO2 from flue gases, as is now to be done in Zurich, is not yet known in Switzerland. This requires specialists and new regulations. How difficult it is to find this know-how became apparent during the development of the project: only one company took part in the city’s tender.
Brunner believes the city’s plans make sense. Extracting and permanently storing CO2 for climate protection is a global task and a method that will become established in the coming decades. “We need pioneers today to gain experience for later. Otherwise there will be no technological learning curve.” The city of Zurich also wants to capture CO2 at the Hagenholz waste incineration plant one day. This involves a much larger amount, namely 360,000 tons.
The new CO2 capture plant in Zurich costs 35.5 million francs, plus annual recurring expenses of 14 million francs. That’s a lot of money. Brunner says: “CO2 removal is the most expensive measure in climate protection. But leaving CO2 in the atmosphere is much more expensive in the long term.”
With larger facilities and improved know-how, the costs of capturing CO2 will one day be reduced. The cost-benefit ratio is also right. The removal and storage account for around 10 percent of the amount of CO2 captured. That is a good figure, says Brunner. Transport from Zurich to the north is carried out by truck, train and ship. The city expects that five to seven trucks per day will leave Werdhölzli heading north.
Brunner believes the biggest challenge for the city’s project is the skepticism towards new things. But he is confident that this will disappear. “In principle, we are doing nothing other than a new form of waste disposal.”
Brunner makes a comparison: Until 60 years ago, wastewater was discharged directly into the water. Swimming in rivers and lakes was unthinkable. Then sewage treatment plants were built – and the water was clean. We see that as completely normal today.” With CO2 capture, it will one day be the same.
FDP: “Insanely high costs”
The proposal found a clear majority in the city parliament. Only the SVP rejected it, particularly with reference to the high costs. Capturing CO2 in Zurich and transporting it across Europe is greenwashing, criticized SVP man Johann Widmer in the council.
The FDP, on the other hand, welcomes the city’s plan in principle. “We see it as a pilot project that needs start-up funding,” says municipal councilor Emanuel Tschannen. “Zurich has the best universities in Switzerland and is a technology capital, so it can make advance payments.”
However, the Liberals are critical of the costs. These are “incredibly high,” says Tschannen. “The city generally builds expensively, and no savings were made on this project either.” He criticizes in particular that half of the running costs are spent on transporting the liquefied CO2. Tschannen emphasizes that the FDP’s yes does not automatically mean approval for future projects. The planned CO2 capture in Hagenholz can only be approved if the economic viability is better.
The Greens also support the proposal in principle – but they caused discussion in the parliamentary group, explained Matthias Probst at the council debate. He himself rejected the plan. He was concerned about a local pilot plant being built in Switzerland and the CO2 being shipped abroad, Probst told the council: “It is not productive to only optimize our balance locally, even though this is a global problem.” In his view, it would make more sense to work on ensuring that CO2 can also be stored in Switzerland.
Theoretically, this is possible, says ETH researcher Brunner. A research project is currently underway at ETH in Trüllikon. Nagra is making a disused borehole available to science there. “The question is how much CO2 can be stored per year.”
This is only profitable with larger quantities. According to Brunner, the geology in Denmark and Norway is well suited to storing CO2 permanently. In addition, these countries already have the expertise for the necessary drilling and regulations.
There is probably no way around transporting it north if we want to capture CO2.
