Large scale cultivation of Hydrogenobacter thermophilus on hydrogen

The thermophilic hydrogen‐oxidizing eubacterium, Hydrogenobacter thermophilus was grown with a semi‐continuous gas feed in a 150 1 fermentor, on different ratios of H₂, O₂ (air) and CO₂ and on media of variable mineral salts composition. The best gas ratio during the exponential phase was approximately 0.5:1.0:0.03 atm of H₂: air: CO₂. Cell densities were increased by increasing the concentration of ammonium and phosphate in the medium. The maximum cell density obtained under the most favourable conditions was 2.62 g wet wt 1^‐1, corresponding to an absorption of 1.6 at 600 nm. The maximum specific growth rate (u) was 0.44 h^‐1.