Life cycle assessment of bio-based fertilizers production systems: where are we and where should we be heading?

PurposeDespite the industrial and scientific acceptance of life cycle assessment (LCA) to determine the environmental performance of products, none of the existing information on LCA provides explicit and clear recommendations on how to apply it when evaluating bio-based fertilizer (BBF) production systems. This situation affects the reliability of the results and causes confusion among practitioners, technology developers, and other stakeholders. Here, we first present the practitioners' current LCA methodological choices and then discuss the extent to which LCA standards and guidelines are correctly applied. This review intends to identify LCA methodological application hotspots towards the definition of consensual LCA methodological choices for BBFs.MethodLCA studies for BBF production systems were reviewed together with currently available LCA standards and guidelines to define which LCA methodological options are adopted by LCA practitioners in the first place, and then to determine whether these options are within the framework of existing LCA standards and guidelines. The results obtained are presented and discussed to finally debate and evidence the need for consensual LCA methodological choices for BBFs.Results and discussionA total of 48 documents were reviewed between LCA standards and guidelines (8) and studies (40). Most of the reviewed studies state that BBFs are the main product of the system (30), while the remaining ones state them as secondary products. Although the standards and guidelines statements are interrelated, it is challenging to follow their recommendations when applied in studies evaluating BBF production. For instance, LCA studies do not clearly define the studies' promotor, motivation, and specific research question which leads to a lack of justification regarding the taken choice between attributional or consequential LCA. Therefore, the next LCA methodological choices such as functional unit, allocation criteria, biogenic carbon management, and end-of-life status of feedstock, are not justified.ConclusionIt has been evidenced that the lack of consensual LCA methodological choices is affecting the proper use of the LCA by practitioners that aim to assess BBFs production systems. Thus, it shall be imperative for researchers and technology developers to work on the definition of common LCA methodological choices. This study has concluded that more guidance on the process of defining the study's promotor, motivation, and specific research question is highly needed by practitioners since this would lead to the definition of common goals and scopes, first, and then, set the path to define standard LCA methodological choices.