MO.2.D || Carbon Inventory and Management of Bio-Based Materials for a Post-Fossil Bioeconomy

Azzi, Elias; Karltun, Erik; Sundberg, Cecilia

Biochar is a bio-based material with long lifetime, which is already commercially available for use in urban greening in Sweden. New products are also under development such as water filters and concrete with biochar. As a carbon dioxide removal technology, biochar use in urban products raises challenge for the life cycle assessment (LCA) of individual products and the management of carbon sinks at the urban-scale. In product LCA, large variability is expected because the biochar content of a product is often set by volume. For management of carbon sinks, the decadal lifetime of biochar products raises concerns over the fate of the embodied carbon sink when the products reach end-of-life. We modelled the LCA of 5 biochar products (urban tree, green roof, landscaping soil, charcrete, filter), with 7 different biochar supply-chains (4 biomass types, 3 pyrolysis reactors). These applications where benchmarked against conventional products. Using dynamic material flow analysis (dMFA), we then modelled the biochar demand for a new city-district in Uppsala, Sweden, from 2020 to 2100. The climate impact of biochar products was mainly influenced by the bulk density and carbon content of the biochar. In a decarbonised energy system, the variations induced by reactor type, reference land or biomass use, and supply of other materials were of smaller importance. The climate benefits of using biochar in a decarbonised energy system ranged from -4.8 to -1.3 t CO2/t biochar for pelletized biomass, and from -7.2 to -0.57 t CO2/t biochar for non-pelletized biomass. For Uppsala’s new district, biochar demand was around 2500 m3/year during the 25 years of construction and dropped by 80% thereafter. Landscaping soil for parks was the largest biochar consumer. By 2100, 72% of produced biochar would be accumulated in parks, and 15% of biochar in landfills. Combining dMFA and LCA appeared useful for studying biochar carbon flows and stocks.