Performance of a pilot scale pressurized deep-jet gas bioreactor for SCP production with Cupriavidus necator H16

Single cell protein (SCP) production has the potential for significant contribution to global protein supply. The ground-breaking approach presented here demonstrates the industrial potential of Cupriavidus necator H16, a chemolithoautotrophic bacterium uniquely capable of converting CO₂ into high quality SCP. The study, conducted in a custom 300-L pressurized deep-jet bioreactor optimized for extremely efficient gas-liquid transfer, provides crucial insights for scalable SCP production. It highlights the significant influence of the inoculum type on the efficiency of fermentation. Heterotrophic inoculum caused a 10-hour lag phase, which limited the efficiency of the fermentation process, while chemolithoautotrophic inoculum achieved almost immediate productivity without a lag phase. This marked difference in performance underscores the importance of inoculum selection in maximizing yield. Fermentation with chemolithoautotrophic inoculum reached 300 g L^-1 cell wet weight (CWW) in only 35 h - a remarkable 44 % faster than the 63 h required with heterotrophic inoculum. By repeated removal of larger broth samples, the biomass concentration could be further increased to 360 g L^-1 CWW, which corresponds to to 90 g L^-1 cell dry weight (CDW). This demonstrates the feasibility of continuous operation and scalable production. The highest gas transfer and consumption rates were observed approximately 35 h after the start of fermentation: H₂ at 0.82 kg h^-1, O₂ at 4.1 kg h^-1and CO₂ at 1.95 kg h^-1. These high transfer rates underline the efficiency of the bioreactor in gas utilization, a critical factor for industrial-scale applications. The biomass showed a very high crude protein content of 80 % with an amino acid profile comparable to that of commercial fishmeal. This positions the SCP as a high-quality, sustainable alternative for application in aquaculture and poultry feed, meeting global protein needs while reducing environmental impact.