Cities100: Stockholm - World’s First Urban Carbon Sink with Biochar

The Stockholm Biochar Project is turning the city’s park and garden waste into renewable energy for heating while sequestering carbon.

The Challenge

Cornell University estimates that producing biochar from biomass – such as organic waste that does not compete with food production or increase land use – could sequester carbon equivalent to 12% of global CO2 emissions, which is on par with emissions from the global transport sector. As any type of clean organic material can be used to make biochar, the Stockholm Biochar Project paves the way for cities to create urban carbon sinks from their organic waste.

The Solution

The Swedish capital of Stockholm is building a pyrolysis plant, which allows the city to produce biochar and renewable energy from its green urban waste. By 2020, the energy generated from biochar production will be turned into 25,000 MWh of heat for the city’s district heating network, enough to heat 400 apartments.

With current levels of global greenhouse gas emissions, there is an urgent need to lower the level of carbon dioxide in the atmosphere. The Stockholm Biochar Project does just this by turning park and garden waste, which contain carbon taken up through photosynthesis, into biochar. Biochar sequesters carbon by converting it into a stable element of the soil that can stay in the ground for millennia. The biochar serves as a substitute for finite materials, such as peat, clay, and sand, and is used by the city in public plant beds – creating the world’s first urban carbon sink. The Stockholm Biochar Project plans to produce 7,000 metric tons of biochar by 2020, which sequesters carbon equivalent to the yearly CO2 emissions from 3,500 green cars.

Environmental Benefits – 6,500 metric tons of organic waste will be turned into a resource every year by the Stockholm Biochar Project.

Social Benefits – The project aims to have 100,000 residents using biochar in their gardens by 2020.

Economic Benefits – Park and garden waste is difficult and costly for Stockholm to dispose of. When processed by the Stockholm Biochar Project, this waste can help lower the overall cost of waste management and generate an income from selling heat

About Cities100

Presented by C40 Cities Climate Leadership Group (C40), Sustainia and Realdania – Cities100 showcases leading solutions to urban climate challenges in ten sectors, ranging from solid waste management to transportation.

Available online and in print, Cities100 provides stakeholders an accessible format to explore achievable solutions for climate action in cities, and will be a useful tool for relevant groups ranging from impact investors and development organizations, to mayors and city governments.  You can access the full Cities100 2015 publication online here.