Empowering microbial proteins: Continuous electro-fermentation of hydrogen-oxidizing bacteria from water, urea and carbon dioxide

The global demand for sustainable protein sources is driving research into microbial protein production, with hydrogen-oxidizing bacteria identified as particularly promising candidates. This research investigates the optimization of nutrient assimilation and biomass (protein) production in a continuous electro-fermentation process. A deeper understanding of substrate consumption patterns in long-term, continuous operation, an often overlooked aspect, will be key to maximizing both productivity and process stability. In this study, oxygen and hydrogen were produced in situ through water electrolysis, while carbon dioxide and urea-derived nitrogen were used as the main nutrient sources. Over 500 days of continuous operation, the process maintained stable performance while production was progressively enhanced through targeted adjustments in operating conditions. While stable operation consistently yielded 2.6–2.8 g TSS L⁻¹ d⁻¹, peak productivity of 3.7 g TSS L⁻¹ d⁻¹ was reached at a 20-h hydraulic retention time (HRT) under high hydrogen availability, highlighting the importance of balancing nitrogen supply and HRT to achieve sustainable microbial protein production. Under optimized conditions, biomass protein content reached 90 %, demonstrating the potential to modulate biomass composition through operational strategies. These findings provide new insight into the stoichiometric balance of electro-fermentation and its potential for scalable, sustainable protein production.