04/09/2021
In a bid to become more sustainable, Stockholm has found an unusual ally, old Christmas trees and other garden debris. The Swedish capital is using green waste to power homes and reduce its carbon footprint.
People around the city are gathering up garden waste and dead Christmas trees from fellow residents and city parks, and turning it into an eco-friendly type of charcoal called biochar.
Produced via a special chemical process, biochar helps boost tree growth, improves soil quality and traps large amounts of carbon dioxide. Biochar is created when organic waste, such as fallen tree branches and dead plants, are heated at 200-400°C with little or no oxygen, in a process known as pyrolysis.
Normally, burning organic matter at such high temperatures would generate large amounts of methane or carbon dioxide emissions. But with biochar, the carbon is trapped in solid form.
Is biochar the future?
The Intergovernmental Panel on Climate Change (IPCC) highlighted biochar as a promising technology for keeping CO2 out of the atmosphere in its 2018 report. And according to a study by Cornell University in the US, producing biochar from organic waste could offset as much as 12 per cent of global emissions, equivalent to the carbon footprint of the global transport sector.
When biochar is buried in the soil it acts as a carbon sink, storing CO2 for thousands of years. Once in the ground, it fertilises the soil and boosts plant growth significantly.
“We have a process where we are taking carbon from the atmosphere and binding it back into the soil,” says Jonas Dahllof, founder of the biochar project and planning director at Stockholm’s water and waste department.
Dahllof says the Stockholm authorities decided to produce their own biochar after seeing the impact it had on local biodiversity.
Sweden is the latest country to use biochar, generated from green waste, to power its homes.
