Circular agriculture design: Integrated biorefinery to convert agri-residues into novel opportunities

As the world's population grows and agricultural production increases, biorefineries are emerging to convert the resulting residues into bioproducts. However, most agri-residues remain unused, and expected new markets and independence from fossil- and crop-based equivalents have not materialised. In this work, a group of international experts has identified key gaps and interdependencies in integrated biorefinery systems, and proposed strategies to improve their efficiency, compatibility, and scalability. A particular attention is given to protein and polyester production to address the overlooked global protein deficit and persistent plastic pollution, respectively. First, early-stage guidance on embedding complex circularities is discussed to ensure safety and sustainability requirements are met. A dedicated Safe-and-Sustainable by-Design (SSbD) framework needs to be developed and integrated into a decision-support tool to, for example, prevent potential enrichment cycles of biological and chemical contaminants. Among the identified technical barriers, improving bioactive compound recovery through eco-friendly extraction processes, using specific enzymes, natural deep eutectic solvents and/or ionic liquids, is analysed. Simultaneously, valorisation of downstream residual flows should be ensured. Promising improvements of complementary biological conversion pathways have been identified at three levels to balance flexibility, cost, quality, and scalability: (i) upstream mild pre-treatment to convert resistant residues into carboxylate precursors (e.g. thermophilic hydrolysis); (ii) midstream high-performance microbial fermentation (e.g. continuous reactors, co-production of microbial proteins and polyhydroxyalkanoates (PHAs) of different chain lengths); and (iii) downstream recovery strategies (e.g. using predatory bacteria or insects digestion). Lastly, a novel frugal-by-design thinking is introduced to tailor bioproducts’ performance to what is just necessary for end-users. • Agri-residue biorefineries require a Safe and Sustainable by Design framework • SSbD prevents contaminant enrichment; Bioactive extraction aligns with cascading • Upstream thermophilic hydrolysis converts resistant residues into precursors • Midstream fermentation enables microbial protein and PHA co-production • Downstream biological PHA recovery; Frugal-by-design tailors bioproduct performance