Pilot-scale electricity-driven production of single-cell protein from CO₂ by hydrogen-oxidizing bacteria

Hydrogen-oxidizing bacteria (HOB) offer a promising route for sustainable single-cell protein (SCP) production from CO₂ and renewable electricity, but most studies remain limited to low-productivity laboratory scale. Here, we developed a 100 L pilot-scale electrolysis-fermentation ex-situ coupled system, in which H₂ and O₂ generated by water electrolysis were directly supplied to a gas fermentation reactor for autotrophic CO₂ fixation by a HOB community under ambient pressure. Through optimizing the operating parameters and implementing process intensification strategies, the system achieved a maximum biomass productivity of ∼12 g CDW L⁻¹ day⁻¹, with an average productivity of 10.8 ± 0.6 g CDW L⁻¹ day⁻¹, higher than many previously reported laboratory-scale systems. The biomass contained ∼60% crude protein with an indispensable amino acid profile comparable to fishmeal. Preliminary techno-economic analysis and carbon emission assessment further revealed that although the current pilot-scale process remained marginally unprofitable (−¥2150 t⁻¹ SCP), it exhibited a very low carbon emission per ton of product (7.2% of fishmeal and 30% of soybean meal). Overall, this study demonstrates the engineering feasibility and environmental advantage of electricity-driven CO₂-to-protein production at the pilot scale, providing an important step toward large-scale sustainable protein manufacturing.