In collaboration with Stockholm Vatten och Avfall and the City of Stockholm, we operate a biochar plant in Stockholm. The site includes a state-of-the-art charcoal kiln where biomass in the form of garden waste is heated without oxygen, which means that the charcoal remains instead of being fully burnt and forming carbon dioxide. The process generates heat which we recycle into the district heating network and distribute to Stockholmers.

The project is partly funded by Bloomberg Philanthropies through prize money in the Mayors Challenge innovation competition.

15% of Stockholm’s garden waste is turned into heat and biochar

Garden waste is obtained from Stockholmers who leave it at one of Stockholm Vatten och Avfall’s recycling centres. Biochar is then buried in parks and gardens to improve the quality of the soil and bind carbon in it. This currently creates a very small carbon sink, but the technology is now in place and can be scaled up.

Our existing plant can handle around 15 per cent of Stockholm’s garden waste. We are working on expanding this anount with more biochar facilities.

Is there a market for biochar?

Currently, biochar is mainly seen as a way of improving soil quality, but extensive research is being conducted into biochar internationally, for example because it can, among other things, reduce emissions caused by meat production, while at the same time becoming a component of natural fertilizer. There are several other possible uses, including filler in concrete, as filter materials, or as additives in animal feed.

How we’re working to create negative emissions

We’re testing and developing two different technologies.

In line with the Paris Agreement

The production and consumption of energy has historically been associated with greenhouse gas emissions, but through district heating with negative emissions, the reverse is possible. The technology behind negative emissions reduces the amount of carbon dioxide in the atmosphere in line with efforts that must be made to cope with global warming under the auspices of the UN Paris Agreement.

There are several methods for extracting and storing carbon dioxide from the atmosphere, processes that create what is known as “negative emissions”, carbon capture, or carbon sinks. Stockholm Exergi is focusing on two key approaches, both of which are based on photosynthesis:

Bio-CCS involves the separation and storage of carbon dioxide formed during the combustion of biofuel. With the support of the Swedish Energy Agency, Stockholm Exergi installed a Bio-CCS research facility at our bio-cogeneration plant. The plant opened in December 2019. The same technology can be used to separate carbon dioxide from waste incineration. This also gives rise to negative emissions, but not to the same degree as with biofuels.

The second method for creating negative emissions is to produce biochar in modern charcoal kilns. The kilns bind carbon dioxide and store it stably in biochar, which is a powerful soil improver and acts a carbon sink.

Considerable potential

There is considerable potential to create negative emissions in the Stockholm region. A comprehensive report commissioned by the City of Stockholm shows that bio-CCS and biochar have the potential to reduce climate impact to a far greater extent than other measures. The report also shows that the costs associated with these technologies are lower or similar to other measures.