Sustainable and safe single-cell protein production via passive gas-feeding under ambient conditions in resource-limited regions

Abstract

Aerobic hydrogen-oxidizing bacteria (Cupriavidus necator H16) demonstrate efficient non-phototrophic CO₂ assimilation for single-cell protein (SCP) production using H₂ as an energy source. However, achieving high productivity in remote or resource-limited regions is often hindered by challenges in continuous gas supply, utilization, and control. In this study, we proposed a simplified proof-of-concept SCP production line that integrates green energy with a custom-designed fermenter. Utilizing a novel passive gas-feeding strategy driven by concentration differentials between gas and liquid phases, the single-chamber fermenter achieved biomass productivity of 58 mg L⁻¹ h⁻¹ with minimum waste gas generation. Furthermore, we found that low dissolved O₂ (<1 mg L⁻¹) and ammonium concentrations (<2 g L⁻¹) were crucial factors limiting SCP production in biomass (<50%) when bacterial OD₆₀₀ reached around 5. To further address safety risks associated with H₂–O₂ mixtures, a dual-chamber fermenter was designed to separate the passive flow of H₂/CO₂ and O₂ derived from ambient air. This innovative system facilitates efficient gas utilization and nutrient exchange without gas loss, enabling safe and effective small-scale applications under atmospheric pressure. These results provide a promising approach for enhancing continuous gas fermentation efficiency and addressing safety concerns in SCP production in resource-limited communities.