Spatial separation of hydrogen and oxygen gas in SCP production by hydrogen oxidizing bacteria: a theoretical energy-efficiency assessment

A novel approach to single-cell protein (SCP) production via hydrogen-oxidizing bacteria (HOB) is introduced to minimize explosion risks in hydrogen-based bioprocesses while assessing its implications for renewable-energy-based protein production systems. An alternative process is proposed where hydrogen (H₂) and oxygen (O₂) are spatially separated into two compartments: bioreactor and regenerator. Hydrogen is combined with an alternative electron carrier in a bioreactor, while oxygen is directed to a second compartment where the electron carrier is regenerated and energy is recovered. A thermodynamic analysis was performed to estimate yields and energetic efficiencies with a 13% margin of biological variability. Alternative processes based on HNO₃ as electron carrier showed the highest potential when reduced to N₂, NO, or N₂O at low pH. Energy demand for SCP production was estimated to be 5.26, 5.82, and 5.52 MJ/mol_protein, respectively. This was comparable to the 5.47 MJ/mol_protein when using O₂ as electron acceptor. The estimated yields for HNO₃ reduction to N₂ were in accordance with empirical biological yields. This showed that HOB-SCP energetic efficiency could be competitive with that of the conventional single-compartment aerobic method, offering a comparable energy demand, and a more integrated process design while eliminating explosion risks. This perspective on energetic efficiency is crucial for feasibility and techno-economic analysis of hydrogen-based SCP as a renewable-energy-driven route for sustainable protein production.