Ethanol production in biorefineries using lignocellulosic feedstock - GHG performance, energy balance and implications of life cycle calculation methodology

摘要

Co-production of high-value biobased products in biorefineries is a promising option for optimized utilization of biomass. Lignocellulosic materials such as agricultural and forest residues have been identified as attractive alternative feedstocks because of their high availability and low resource demand. This study assessed the greenhouse gas (GHG) performance and energy balance of ethanol co-production with biogas and electricity in biorefineries using straw and forest residues. Two calculation methods were used: Method Ⅰ (ISO), which applied the international standard for life cycle assessment, and Method Ⅱ, which applied the EU Renewable Energy Directive (RED) methodology. These methods differed in allocation procedure, functional unit and system boundaries. Analysis of the importance of significant methodological choices and critical parameters showed that the results varied depending on calculation method, with co-product handling and the inclusion of upstream impacts from residue harvesting explaining most of the differences. Important life cycle steps were process inputs in terms of enzymes and changes in soil organic carbon content due to removal of residues. Ethanol produced from forest residues generally gave lower GHG emissions than straw-based ethanol. The GHG savings for both feedstocks were 51-84% relative to fossil fuel. Omission of upstream impacts from residue recovery in agriculture and forestry in the RED method means that it risks overlooking important environmental effects of residue reuse. Furthermore, the default allocation procedure used in the RED method (energy allocation) may need revision for biorefineries where multiple products with different characteristics are co-produced.