Biomass residues as resources: An expanded life-cycle perspective

Biomass residues have been identified as potentially promising resources for production of bio-based products and fuels with low climate impacts. Unlike primary biomass such as crops, using residual biomass may avoid issues such as competition over land for food and feed production. To assess the climate impacts of products made from residual biomass, a life cycle assessment (LCA) may be used, but its results are known to be sensitive to method choices. The aim of this thesis, therefore, is to better understand and illustrate how different assessment approaches affect conclusions regarding the climate impacts of different management alternatives for biomass residues.
Different factors affect either the greenhouse gas emissions related to valorisation of biomass residues, or the climate impacts of those emissions. These factors range from the design of valorisation processes, including the use of enzymes and energy carriers in production, to the way LCA is applied, including how the upstream processes that the residues come from are considered, and the way in which CO2 fluxes from biomass are considered in the assessment. Finally, the method used for climate impact assessment can affect the conclusions regarding the climate-change mitigation potential, especially for forest residual biomass. Whether valorisation of biomass residues provides climate benefits therefore depends on how the bio-based products are produced, what they are compared to and when, and on the specific goal of climate-change mitigation.
Valorisation strategies for residual biomass should increasingly consider the upstream processes of biomass residues, as these materials are increasingly considered valuable. When these processes are included in LCA, they can have a significant impact on the conclusions drawn in some cases of residual biomass valorisation. It is also essential to consider other valuable uses of residual biomass materials to sustain long-term productivity and sustainability of primary production systems. Both these strategies are important in circular bioeconomies, but available circularity assessment methods for bio-based products primarily focus on the former, and still fail to consider processes and inputs related to high climate impacts.
The idea of valorising residual biomass into products with low climate impacts is thus more complex than at first sight, and many parameters can affect the conclusions. A better understanding of this complexity can potentially lead to a more nuanced understanding of the possibilities and risks related to using biomass residues as resources.