Life cycle assessment of urban uses of biochar and case study in Uppsala, Sweden

Elias S Azzi,Cecilia Sundberg,Erik Karltun

doi:10.1007/s42773-022-00144-3

Elias S Azzi, Cecilia Sundberg + Show 1 more

Open Access

https://doi.org/10.1007/s42773-022-00144-3

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Abstract

Biochar is a material derived from biomass pyrolysis that is used in urban applications. The environmental impacts of new biochar products have however not been assessed. Here, the life cycle assessments of 5 biochar products (tree planting, green roofs, landscaping soil, charcrete, and biofilm carrier) were performed for 7 biochar supply-chains in 2 energy contexts. The biochar products were benchmarked against reference products and oxidative use of biochar for steel production. Biochar demand was then estimated, using dynamic material flow analysis, for a new city district in Uppsala, Sweden. In a decarbonised energy system and with high biochar stability, all biochar products showed better climate performance than the reference products, and most applications outperformed biomass use for decarbonising steel production. The climate benefits of using biochar ranged from − 1.4 to − 0.11 tonne CO2-eq tonne−1 biochar in a decarbonised energy system. In other environmental impact categories, biochar products had either higher or lower impacts than the reference products, depending on biochar supply chain and material substituted, with trade-offs between sectors and impact categories. However, several use-phase effects of biochar were not included in the assessment due to knowledge limitations. In Uppsala’s new district, estimated biochar demand was around 1700 m3 year−1 during the 25 years of construction. By 2100, 23% of this biochar accumulated in landfill, raising questions about end-of-life management of biochar-containing products. Overall, in a post-fossil economy, biochar can be a carbon dioxide removal technology with benefits, but biochar applications must be designed to maximise co-benefits.

Highlights

Several cities in Sweden have set ambitious climate and socio-environmental goals
A major carbon dioxide removal (CDR) technology deemed possible in Sweden is biochar production and use
Our results demonstrate the importance of biochar product manufacturers disclosing the volume content of biochar, and disclosing other biochar supply chain information, e.g. biomass origin, pyrolysis conditions, and biochar properties

Summary

Introduction

Several cities in Sweden have set ambitious climate and socio-environmental goals. A major carbon dioxide removal (CDR) technology deemed possible in Sweden is biochar production and use. The carbon-rich residue derived from biomass pyrolysis (Lehmann and Joseph 2009), is regarded as having a higher readiness than other CDR technologies as it is already available at small and medium scales, while large-scale reactors are being developed (Nemet et al 2018). The most well-established application of biochar in Sweden is in constructed soils in urban environments. Trees planted in hard-paved areas, suffering from soil compaction, have been re-planted in blends of macadam, biochar and compost since 2012 (Stockholm Stad 2020). Biochar-macadam structural soils are used for tree planting and rain-gardens in several Swedish cities, contributing to storm-water management. Several soil manufacturers offer landscaping soil containing biochar as part of their standard catalogue (Hasselfors 2021)

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