Environmental impacts of cereal straw pellets in biogas systems: A comparative life cycle assessment

Anaerobic digestion (AD) of straw pellets is a promising technology for the production of renewable energy by tapping into previously unused material, as straw pelleting offers advantages in terms of transportation, handling and methane production potential of the material. A life cycle assessment (LCA) was carried out in accordance with ISO 14040/14044 across the entire process chain, from grain cultivation to digestate utilization, with different scenarios for the provision of straw and straw pellets as well as biogas substrate mixtures. The results of the LCA showed that a reduction in emissions can be achieved in some environmental impact categories such as global warming potential (GWP) or particulate matter formation (PM). However, the environmental impact of using straw pellets as a biogas substrate depends on the underlying boundary conditions, such as the choice of allocation method for grain cultivation, transportation distances, pelleting technology or the substrate mixture for AD used. Overall, the LCA reveals that a suitable substrate mixture incorporating straw pellets with other agricultural residues can reduce the environmental impact of biogas production and thus contribute to a sustainable supply of renewable energy.