Allocation in LCAs of biorefinery products: implications for results and decision-making

Abstract

In Life Cycle Assessments (LCAs) of biorefinery products, a common challenge is the choice of method for allocating environmental burdens of multifunctional processes (feedstock cultivation and biorefinery processes), a choice which can substantially influence LCA results and hence decision-making. The aim of this paper is to explore how this choice influences results and in which decision contexts the choice is particularly important. To do this, we tested six allocation methods in a case study of a biorefinery using pulpwood as feedstock. Tested methods included: main product bears all burden, substitution, traditional partitioning methods (based on economic value and exergy), a hybrid method combining elements of substitution and partitioning, and an alternative hybrid method developed by us, which allocates less environmental burden to co-products with a high potential to mitigate environmental burdens. The methods were tested in relation to decision contexts and LCA questions of relevance for biorefineries.The results indicate that the choice of allocation method deserves careful attention, particularly in consequential studies and in studies focussed on co-products representing relatively small flows. Furthermore, the alternative hybrid allocation method is based on a logical rationale – favouring products with higher substitution potential – and has some other potential benefits. However, in cases where the scales of co-product flows are of different orders of magnitude, the method yields extreme results that could be difficult to interpret. Results also show that it can be important with consistent allocation for both cultivation and biorefinery processes, particularly when substitution is applied.