Upcycling of biowaste carbon and nutrients in line with consumer confidence: the “full gas” route to single cell protein

Abstract

Circular management of carbon and nutrients is at the basis of future environmental sustainability and global food safety. However, direct resource recovery and upcycling from wastes pose safety concerns related to source contamination. By carefully evaluating the potential integrations of existing and emerging bio-technologies, we put forward new possible pathways for the clean-tech upcycling of recovered carbon and nutrients. By coupling anaerobic digestion and thermochemical gasification, the key process line converts biowastes to clean gaseous substrates (e.g. H₂, CH₄, CO₂, CO, NH₃, P₂), useable for the fermentative production of safe single cell protein (SCP). The subsequent direct (aerobic) or two-stage (anaerobic/aerobic) SCP fermentation of energy-rich gases can produce protein-rich microbial biomass. Worldwide, this is estimated to generate up to 606 Mt SCP per year, with the protein content more than 3 times the worldwide annual soybean meal protein production. The combined SCP and biochar production can further capture and store up to 2.33 Gt CO₂-eq per year, representing ∼50% of the Paris Agreement target on annual carbon capture. Finally, this approach could recycle up to 18.5 Mt nitrogen per year (∼8% of current N losses) and 6.5 Mt phosphorus per year (∼25% of the annual phosphorus fertilizer production). In view of a low-carbon and sustainable circular bioeconomy, this concept presents high impact and positive implications, especially in terms of safe future feed and food supply. Producing SCP as a multi-applicable recovery product can be already carried out at production costs that are competitive with those of other feed additives, especially if the social cost of carbon emissions is considered.