Biogas upgrading and valorization to single-cell protein in a bioinorganic electrosynthesis system

Valorization of crude biogas to value-added products is the key step toward techno-economic biogas business. Besides, the increasing world population puts heavy pressure on food supply and will double protein demand in the coming decades. In this context, we propose a bioinorganic electrosynthesis process for the integration of biogas upgrading and edible single-cell protein production, which could be an alternative solution to address these challenges. With a biogas inflow of 70%CH₄/30%CO₂ at 50 mL·d⁻¹ and an applied voltage of 3.0 V, the protein concentration of 472.04 ± 22.05 mg·L⁻¹ was achieved with the “CO₂-to-CH₄” bioconversion efficiency of 92.97 ± 5.61%. Higher CO₂ content in the biogas resulted in a comparatively lower protein concentration. The system was tested resilient to the toxic H₂S in biogas (up to 5000 ppm). It was possible to improve the protein yield three times by scaling up the fermenter from 100 mL to 1 L, with a “CH₄-to-SCP” fermentation efficiency of 70.67 ± 2.37%. The methanotrophic biomass produced in the system was found rich in protein with a total amino acids mass-content of over 62.8%. The outcomes of this study will offer a new solution for sustainable protein production, biogas upgrading and valorization, which are perfectly in line with the United Nations Sustainable Development Goals.