From digestate and CO2 to single-cell proteins: combined by-product valorization for circular carbon and nutrient utilization

This study explores the hydrogenotrophic production of valuable single-cell proteins (SCPs) based on the utilization of CO2 from biogas upgrading and nutrients from digestate, by-product of anaerobic digestion (AD), thus contributing to meet the growing global protein demand in a circular way. Experiments conducted under both aerobic and anaerobic conditions, utilizing synthetic nutrients and CO2, demonstrated faster microbial growth in aerobic conditions with cell doubling time of 15 ± 2 h in aerobic conditions against 44 ± 0.1 h in anaerobic conditions. After identifying the most productive microbial platform, experiments were conducted using CO2 and nutrients from digestate, after a proper pre-treatment for pathogen removal. Overall, the results highlight the potential to produce SCPs from AD by-products, biomass production almost quadrupled and SCP/biomass ratio increasing by 19%, compared to the utilization of synthetic nutrient sources.