System analysis of biochar production and use in Swedish urban and rural areas
Biochar is the solid carbonaceous residue of biogenic organic matter (biomass) thermally degraded under low oxygen conditions (pyrolysis).
An interest for biochar production and use has arisen from possible sustainability synergies (win-win strategies) in the fields of waste management, energy production, soil management and climate change mitigation.
- Waste Management: biochar can be produced from various sources of biomass, e.g. agricultural wastes, urban yard waste, wooden by-products, sludge.
- Energy production: the heat generated during pyrolysis can be used locally or to supply district heating networks.
- Soil management: biochar can improve the properties of some soils, especially regarding water retention, nutrients availability, aeration and organic matter contents. Biochar can also transport contaminants contained in the feedstock to soils (risk) or help remediate contaminated soils (opportunity).
- Climate change mitigation: the high stability of the carbon in biochar may represent a way of increasing the carbon stock of soils over long period of times.
The benefits suggested by various studies in a wide range of fields come with similar risks and trade-off situations. For instance, while it is possible to produce char and recover energy from the process, it is not possible to maximise energy production and at the same time maximise char production for climate change mitigation. Besides, if the lower energy production due to biochar is replaced by fossil fuel combustion, the overall balance is affected. Similar trade-offs apply for most benefits.
Therefore, the assessment of biochar systems is strongly dependent on the local context.
The research aims at modelling the impacts of biochar production and use in the Swedish context, through the development of a systematic methodological framework and its application to three case studies.
Results shall help to better understand the trade-offs and impacts of biochar production on energy systems in Swedish cities, the potential for carbon sequestration and the nutrients and contaminants flows in soils. Suggestions for urban planning may emerge from the modelling and life-cycle assessment routines developed.
In other words, the question to be answered is: where, if anywhere, does biochar makes a difference?
The Stockholm Biochar Project
In 2014, the municipality of Stockholm was awarded a prize in the Mayors Challenge for its biochar project. Since then, a pyrolysis unit (Pyreg 500) fed with urban yard waste (branches and twigs, around 1300 tons/year wet weight) has been installed in Högdalen, Stockholm. Part of the heat generated is fed into the city’s district heating network (equivalent to 80 apartments) while the biochar (300 tons/year) is made available for citizens and used by the City of Stockholm for urban greening trials.
The municipality of Uppsala has set its climate-neutrality goal for 2030 and to become climate positive by 2050. These goals require strategic planning for the energy system and biochar may be one component of the future energy mix. To what extent can biochar production and use contribute to the goals set by the municipality is the question raised here.
Lindeborgs Gård has the ambition of becoming a climate neutral farm. To move forward with this objective, a pyrolysis unit will be installed on-site (Fall 2017). The unit, running on wood pellets, is expected to deliver part of the heat consumed during the winter months (currently provided by a heat pump and the electricity grid) and to produce biochar (around 20 tons over 7 months). The biochar is expected to be partly used for improved manure management, direct soil application and eventually commercialisation of organic fertilisers.
There are opportunities for student project and thesis within the research field. Contact Cecilia Sundberg for more information.
- Cecilia Sundberg, Associate Professor, email: firstname.lastname@example.org
- Elias Azzi, PhD Student, email: email@example.com
- Stockholm Stad
- Fortum Värme
- Stockholm Vatten och Avfall
- Uppsala Kommun
- Lantbrukarnas Riskförbund (LRF)
- Lindeborgs Gård