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Circular Economy (CE) is gaining traction among academics and stakeholders; however, there is no unified framework on how to assess it. This paper proposes a framework that is composed of two segments. The first segment includes circular processes based on the value retention stages of products and systems on different levels. The second segment comprises circular impacts measuring the goals of the CE concerning environmental performance, economic contribution, and social impact. There are eight clusters of circular processes: redesign, reduce, use and reuse, re-sell, refurbish and remanufacture, recycle, recover and recirculate. The review shows that there is a widely spread confusion and overlap between indicators for circular processes and circular impacts. A clear differentiation of each category can significantly improve the tools and methods through which to assess CE. This work aims to provide such differentiation and the foundation for the development of a systematic and standardised CE assessment framework. This review provides relevant guidance of circularity indicators to be used at the (re)design phase of products, materials and systems, as well as the environmental, social and economic considerations that circular strategies must have. Graphical Abstract

Microbial chain elongation using biomass-derived lactate can be steered to produce a variety of medium-chain carboxylates (MCC), which then need to be separated before application. In this study, we evaluated the effects of adding conductive and/or adsorbing materials to batch and continuous open-culture lactate-based chain elongation. Incubation with granular activated carbon (GAC), nickel foam (NF), and stainless steel (SS) mesh improved lactate use for chain elongation due to a ∼30% reduction in propionate formation compared to the control (no material). Isobutyrate production was stimulated in the presence of GAC and NF (up to 1.2 g•L −1 , 9% electron selectivity). Adding GAC to a continuous reactor led to in situ adsorption of ncaproate. GAC showed a high affinity to n-caproate from real and artificial effluents, as well as from blends containing C2−C8 carboxylates, adsorbing 60−80% of the initial n-caproate with recoveries up to 42% after desorption. Adsorption isotherms showed that n-caproate adsorption increased with decreasing pH conditions (184−243 mg•g GAC −1 ). In conclusion, conductive materials changed the product spectrum and steered to isobutyrate formation in batch open-culture chain elongation. Based on the promising adsorption properties of GAC, the first design of chain elongation with in-line adsorption−recovery is proposed as well as potential direct applications of MCC-loaded porous carbons.