A study of the biogeochemical cycle of the biogenic carbon to assess the circularity of bio-based products

The level of circularity of a product or a process is an emerging characteristic in international labelling; however, only fossil-derived materials are evaluated through circularity indices, e.g. the Material Circularity Indicator, MCI, developed by Ellen MacArthur Foundation. This work proposes a complementary index which can serve as Correction Factor (CF) to the MCI, designed specifically for biologically based and renewable materials, such as bio-based products. This index, named MCICFbio, which focuses on the timings of the carbon’s biogeochemical cycle and the effects of human actions on its duration. The bio-based materials can store carbon for a period of time, determined by the lifespan of the bio-product itself. Therefore, MCICFbio quantifies the ‘carbon net savings’ as a function of the effect of the incorporation of Carbon (C) in bio-products on the C cycle duration, compared to a reference system with no bio-based materials production. MCICFbio ranges from 0 to 1, where 0 represents a total carbon loss, 1 total carbon conservation and 0.5 equilibrium, all values being referred to the duration of a cycle of the reference system. Thus, values above 0.5 indicate a gain with respect to the reference system in a given period. The chosen case study (AIB) is the production of bio-based mulch films, tested against two reference systems: a natural prairie (NPR) and a business-as-usual agro-industrial system (AIR). The mulch film life cycle is roughly one year, with a rapid manufacturing process, a short storage and a degradation period in situ assumed equal to five months. The modelling of carbon flows, stocks and feedbacks in different scenarios is conducted through a System Dynamics (SD) approach. Results show that the accumulation of carbon into mulch films delays the carbon release and results in MCICFbio = 0.66 for AIB against NPR and 0.85 for AIB against AIR. Assumptions and limitations of the index are discussed for future research.