A methodological framework for comparing fractionated and non-fractionated products in life cycle assessments: The case of milk concentrates

Fractionation is increasingly applied in the process industries and aids in diversifying the use of biomaterials. However, comparing the environmental impacts of fractionated and non-fractionated products is challenging, since multi-product processes complicate the definition of functional units, and require by-product handling by means of allocation or system expansion. This paper proposes a generic scope-definition framework for multi-product processes in attributional life cycle assessment (ALCA) and in consequential life cycle assessment (CLCA). Considering the potentials and limitations of ALCA and CLCA, this framework addresses the choice of an appropriate functional unit and by-product handling method. Three distinct categories are defined: product systems with identical products, with identical functionalities, and with exclusively identical input materials. The framework is applied to new, fractionated dairy products – micellar-casein concentrate, whey-protein concentrate, and lactose – and their non-fractionated counterpart skim-milk concentrate. The case demonstrates how appropriate functional units can be identified that capture identical specific functionalities. The results for both ALCA and CLCA show that fractionation is environmentally viable. For fractionated products with non-identical functionalities, the methodological choice is reduced to an ALCA yielding a favorable eco-efficiency perspective for fractionation. The framework presented offers a systematic procedure for how to deal with multi-product processes in life cycle assessment that is useful for a wide range of applications.