Environment and Material Science Technology for Anaerobic Digestion-Based Circular Bioeconomy

The circular bioeconomy aims to use resources in the most efficient manner. This includes the conversion of waste and residues, such as organic wastes, into new materials. However, the heterogeneity of organic wastes makes it very difficult to process. In this context, anaerobic digestion has emerged as a core technology to transform this complex organic waste (urban, agro-industrial, or livestock waste) into intermediates that can be further valorized as new commercial products in the so-called waste-to-value biorefineries. Anaerobic digestion initially converts waste of varying compositions into homogeneous intermediates such as biogas (50%–70% CH4) and digestate (rich in nutrients). Applying this organic waste biorefinery concept based on anaerobic digestion, biogas can be cost-effectively converted into biomethane using membrane technology which has benefited from recent advances in material science. Additionally, biogas represents a promising feedstock for the production of new materials such as ectoine and polyhydroxyalkanoates that have the potential to replace fossil-based products. Finally, algal photobioreactors allow for the effective recovery of the nitrogen and phosphorous contained in the digestate. These nutrients are accumulated into the algal biomass that can be further valorized as new bioproducts, thus contributing to create a circular bioeconomy.