Impact distribution methods’ use in multifunctional Life Cycle Assessments: a systematic literature review

Abstract

Partitioning loads related to multifunctional processes, which generate more than one product or service (i.e. function), is a controversial issue within life cycle assessment (LCA). ISO 14044:2006 suggests a hierarchic stepwise procedure. The first step is to avoid allocation whenever possible, through (i) subdividing the multifunctional process into unitary sub-processes with one specific function; or (ii) expanding the system boundaries to include the additional functions related to by-product(s). The second step determines that the system’s inputs and outputs must be allocated based on a fundamental physical relationship between products. When one is unable to identify such physical relationship, flows must be partitioned as to reflect other relations between products, such as their economic value. This paper aims to delineate a scientific overview of the impact distribution methods’ use within LCA practice from 2006 to 2016. Authors performed a systematic literature review and documented methods’ choice frequency within studies published in the considered time frame. Results revealed a lack of consensus among LCA practitioners. Most papers adopt the avoided burden approach (equivalent to system expansion), while the first step proposed in ISO 14044’s hierarchy (subdivision) was actually the least used method. Our examination confirmed that the impact division problem is typically solved by substantially diverging from ISO’s theoretical framework, which suggests both an opportunity for reflection and a reformulation need.

Keywords

• LCA. Allocation. System expansion. Subdivision. Avoided burden. Systematic literature review.