What is this thing called circular bioeconomy? Integrating the concepts of circular agri-food and industrial systems

The meaning of circularity is not fully clear in the context of the bioeconomy, involving the production of biomass and its use for food, biomaterials and bioenergy. Particularly with regard to agri-food systems and the perishable nature of their products, circularity strategies cannot be easily transferred and should be specified. This refers to reducing primary raw materials inputs, extending the product life through reuse, and recycling organic residues to obtain similar products. We provide a definition of circular bioeconomy to clarify what circularity in the context of the bioeconomy means. In a combined approach we analyze shortcomings of available definitions, explain above-mentioned inconsistencies by comparing industrial, agri-food, and natural terrestrial systems, and analyze the 40 most relevant scientific reviews on circular bioeconomy and circular agri-food systems. From this, we extract three properties for a new definition: (i) Biomass flows occur in different states. The substances state refers to relevant material flows. (ii) Making material flows circular means avoiding material losses and consecutively using materials in primary and secondary production and consumption sectors. (iii) Substances are in a dynamic equilibrium between the bioeconomy and the environment. Based on these properties we propose the following definition: “A circular bioeconomy is an economic system, in which biomass and substances contained therein are used consecutively by biomass producing, processing and consuming sectors, resulting in a balanced exchange between the bioeconomy and the environment, where substances neither deplete nor accumulate”. We discuss the system boundary between bioeconomy and the environment and approaches for operationalizing a balanced exchange. Defined as such, circularity is a necessary but not a sufficient condition for sustainability of the bioeconomy.