Technological watch

ABSTRACTCultivating hydrogen?oxidizing bacteria (HOB), such as Cupriavidus necator, using H2 ${{rm{H}}}_{2}$, CO2 ${text{CO}}_{2}$, and O2 ${{rm{O}}}_{2}$ offers a promising route for CO2 ${text{CO}}_{2}$ valorization into chemicals and materials. To enhance cultivation efficiency in a lab?scale gas fermenter lacking a gas recycling system, an automated gas supply strategy based on real?time CO2 ${text{CO}}_{2}$ and O2 ${{rm{O}}}_{2}$ monitoring was developed. Fine?tuning gas delivery is essential to ensure an adequate supply for cellular growth while minimizing excess gas, particularly H2 ${{rm{H}}}_{2}$, that leaves the bioreactor unused, to improve process economics. In the absence of ATEX?compliant H2 ${{rm{H}}}_{2}$ sensors, a soft sensor was implemented to estimate dissolved H2 ${{rm{H}}}_{2}$ concentrations from O2 ${{rm{O}}}_{2}$ uptake rates and growth phase identification. Total gas flow was controlled according to the O2 ${{rm{O}}}_{2}$ requirements of the cells. This strategy reduced overall gas and H2 ${{rm{H}}}_{2}$ consumption by 67%. In addition, a high?cell?density medium was formulated by integrating published recipes with Inductively Coupled Plasma Optical Emission Spectroscopy and nutrient inhibition testing. The optimized medium increased biomass yield from 15 g/L to 53 g/L, with 75% of the dry weight consisting of the bioplastic poly(3?hydroxybutyrate), without requiring nutrient addition or pH control. Together, these strategies improve the scalability, efficiency, and sustainability of CO2 ${text{CO}}_{2}$?based cultivation of hydrogen?oxidizing bacteria.