On 29 March 2017, Ruy Anaya de la Rosa, B4SS project director, attended the launch of the Pyreg pilot pyrolysis plant that has been established as part of the Stockholm Biochar Project, which in 2014, won a €1 million award from the Bloomberg Philanthropies’ Mayors Challenge. The Mayors Challenge is a competition for cities to present revolutionary ideas that aim at solving major problems and that have the potential to be replicated in other cities. The Stockholm Biochar Project is expected to produce 7,000 tonnes of biochar by 2020 and sequester, based on their estimates, an amount of CO₂ equivalent to removing 3,500 cars from the streets of Stockholm. Moreover, the Pyreg plant will burn the pyrolysis gases to generate heat and distribute it through the city’s district heating system to more than 80 apartments.

One of the most innovative features of the Stockholm Biochar Project is its potential to foster citizen engagement in fighting climate change. At home, residents will collect their biomass residues (tree prunings, grass clippings, kitchen scraps, etc), take them to the pyrolysis facility and, in turn, receive a bag of biochar, which can then apply to their balcony pots, window boxes and gardens to promote plant growth. They also receive information about how to use biochar and sequester carbon over long periods of time. According to a survey, 8 out 10 Stockholmers want to be more active in fighting climate change, and the Stockholm Biochar Project offers them a concrete way to do this.

Stockholm has already received almost 100 requests from other cities and organisations that are interested in duplicating the biochar project. Therefore, the Swedish team, led by Mattias Gustafsson, has published a manual with lessons learned and recommendations to bring biochar to your city.

In addition to the launch, Björn Embrén, Stockholm’s tree officer champion and one of the originators of the Stockholm Biochar Project, gave Ruy a tour around the city to see what they have been doing with urban trees. They are basically removing the soil around old standing trees and adding crushed stones (at different sizes according to the depth) with biochar enriched with NPK in an underground structure that includes a well to retain rain water.

Stockholm is mainly replacing old soil with the rocks and biochar mixture to prevent floods in the city (the structures are planned to be able to cope with a 20-year storm), retain water on site to use it during the dry seasons when it is required, and improve nutrient uptake by the trees as their roots do not have to fight compacted soil to thrive and the biochar provides nutrient retention. Furthermore, they are sequestering carbon in the soil in the form of biochar and are having very positive results!

Tack så mycket Björn och Mattias!!