Biohydrogen production from carbon monoxide and water by Rhodopseudomonas palustris P4

A reactor-scale hydrogen (H-2) production via the water-gas shift reaction of carbon monoxide (CO) and water was studied using the purple nonsulfur bacterium, Rhodopseudomonas palustris P4. The experiment was conducted in a two-step process: an aerobic/chemoheterotrophic cell growth step and a subsequent anaerobic H-2 production step. Important parameters investigated included the agitation speed, inlet CO concentration and gas retention time. P4 showed a stable H-2 production capability with a maximum activity of 41 mmol H-2 g cell(-1)h(-1) during the continuous reactor operation of 400 h. The maximal volumetric H, production rate was estimated to be 41 mmol H-2 L-1 h(-1), which was about nine-fold and fifteen-fold higher than the rates reported for the photosynthetic bacteria Rhodospirillum rubrum and Rubrivivax gelatinosus, respectively. This is mainly attributed to the ability of P4 to grow to a high cell density with a high specific H-2 production activity. This study indicates that P4 has an outstanding potential for a continuous H-2 production via the water-gas shift reaction once a proper bioreactor system that provides a high rate of gas-liquid mass transfer is developed