Liquid paraffin gas carrier enhanced the HOB microbial protein production in a bubble column reactor with a gas-liquid mixing pump

Microbial protein (MP) production through autotrophically hydrogen-oxidizing bacterium (HOB) has been regarded as a potential technology for feed or food supply. However, due to the low solubility of O₂ and H₂, how to match the biotic O₂ and H₂ consumption rate and the transfer kinetics presents the key challenge to achieve desired HOB protein production. Here, we introduce liquid paraffin as a gas carrier in a bubble column reactor with a self-priming gas-liquid mixing pump for HOB MP production. The self-priming gas-liquid mixing pump facilitates the efficiency of gas-liquid mixing, while the liquid paraffin improves the solubility of O₂ and H₂. This combined effect optimizes the kinetics of O₂ and H₂ transfer, resulting in an increase in the K_La from 0.69 to 1.81 h⁻¹ for O₂, and from 0.37 to 1.67 h⁻¹ for H₂. Consequently, the yield of NH₄⁺-N to HOB protein increased from 4.21 ± 0.18 gMP∙gN⁻¹ to 5.18 ± 0.68 gMP∙gN⁻¹, and an average protein content of 53 ± 5 % in dried biomass was achieved with nearly 100 % O₂ and H₂ uptake after adding liquid paraffin. The essential amino profile analysis shows that the presence of liquid paraffin has no remarkably impact on the protein quality. These results demonstrate that integration of gas carrier and reactor design is viable to address the gas transfer limitation in the MP production.