The energy efficiency of carbon dioxide fixation by a hydrogen-oxidizing bacterium

Fixing carbon dioxide (CO₂) with solar hydrogen (H₂) is a novel alternative to conventional photosynthesis of plants and microalgae. The energy efficiency of CO₂ fixation by a hydrogen-oxidizing bacterium was investigated in a closed reactor system. The molar ratio of consumed H₂ and CO₂ was measured under mass transfer limitation in atmospheres of sufficient H₂, low CO₂, and a broad range of O₂. The energy efficiency, ranging from 10% to 60%, was primarily affected by the oxygen concentration (6–30 mol%). The research revealed a clear trend that a low oxygen concentration gave high energy efficiency, but slow gas consumption. A high energy efficiency of 50% was measured under a moderate oxygen concentration (10 mol%). Based on 10% solar hydrogen efficiency, a 5% overall efficiency from solar energy to biomass can therefore be achieved.