Sustainability 2022 , 14 , 2619
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Regarding allocation choices made on the basis of individual judgments (highest respective weights), people with a finance or controlling background preferred economic partitioning (3 out of 6 AHPs) over system expansion (2 out of 6) and physical partitioning (1 out of 6). People with a professional background in production, however, executed the (sub-)criteria weightings such that physical partitioning would have been chosen most of the times (6 out of 8 cases; 2 led to economic partitioning). Meanwhile, the judgments made by research and development employees resulted either in the choice of economic partitioning or physical partitioning (3 out of 7, respectively; 1 rating resulted in system expansion). The final choices derived from the aggregated results (using geometric means) led the aggregated professional groups production (43.98%) and R&D (37.41%) to choose physical partitioning for both, and led the aggregated group of practitioners from finance and controlling (34.35%) to choose economic partitioning. 4. Discussion Unlike previous studies that applied different allocation approaches to compare the outcomes [6,14,22] or suggested new case specific approaches [59,60], this study applied user preferences regarding the identified (sub-) criteria to determine how allocation meth- ods would be selected by practitioners. The potential environmental or economic impacts of biorefinery implementations have been assessed several times [5,7,61]. However, major variations are observed in the results of these assessments, with allocation choices in multifunctional processes representing one of the key issues that affects the final outcome [6,13,14]. Both the companies themselves and their stakeholders assign importance to allocating costs and environmental impacts to the products. Thus, determining the respective impacts of and attaining information about each product in the production process is also important [19,23,62]. As a reasonable number of scientific papers are available that address the issue of allocation from various theoretical and applied viewpoints, it was possible to identify several distinct characteristics of allocation methods that may guide practitioners’ choices (RQ1). Nine potential features were derived from these papers. Although some of these features are reported frequently (e.g., market mechanisms), others are cited as single cases (e.g., referring to small quantities of byproducts). Hence, this type of comprehensive overview was performed for the first time, allowing five criteria (and two subcriteria) to be defined that can be applied to choose allocation methods. The resulting decision hierarchy provides guidance on how an allocation method could be chosen easily and transparently for a specific context in practice. The overall results of the assessment indicate that no clear preference for a specific allocation method could be identified among the participants (physical partitioning was favored slightly over economic partitioning and system expansion). Furthermore, the different criteria (based on methodological characteristics), which were relevant for the selection of allocation methods (as shown in Figure 3), were rated rather indifferently, with most average weights (geometric means) hovering around 0.2 (RQ2). Only the criterion flexibility was perceived as relatively less important, and system stability as slightly more important. The respondents weighted the criteria for allocation method selection in different ways: the economic criterion showed higher levels of variation than calculability and interpretation, which indicates that the less constant factors might be more decisive under variable conditions. To a certain degree, these results may reflect (or are reflected by) the ongoing academic discussion on allocation methods [14,19,63]. High ratings assigned to the criterion market environment (subcriterion of economic) and—to some extent—flexibility, favor system expansion, while ability to bear (subcriterion of economic) favors economic partitioning (Figure 4). This finding reflects those of Ekvall and Finnveden [37], who showed the better fit of certain allocation procedures in specific situations. According to Heijungs and Guinee [38], the strength of system expansion in terms of flexibility and consideration of the (dynamic) market environment [17] is also its disadvantage, depending
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