Biohydrogen Production from Carbon Monoxide and Water by Rhodopseudomonas palustris P4

摘要

The hydrogen (H2) production capability of Rhodopseudomonas palustris P4 via water-gasshift reaction of carbon monoxide (CO) and water was studied in batch and continuousbioreactors. Important parameters investigated included agitation speed, inlet COconcentration and gas retention time. Although isolated by the ability growing on CO underlight, P4 showed a better growth under an aerobic/chemoheterotrophic condition than ananaerobic/photosynthetic condition. Hydrogen production, however, was observed under theanaerobic conditions only. In order to maximize H2 production, bioreactor experiment wasconducted in a two-step process, an aerobic/chemoheterotrophic cell growth and a subsequentanaerobic H2 production. When the culture was transferred from an aerobic growth to ananaerobic condition, the CO-dependent H2 production activity of P4 was induced after a lagtime of 50 h. Once induced, the culture showed a stable H2 production capability with amaximum activity of 41 mmol H2/g cell h during a continuous operation of 400 h. At aconstant inlet CO concentration of 10% (v/v) and inlet gas flow rate of 500 ml/min, thevolumetric H2 production rate and CO conversion efficiency increased from 1.1 mmol H2/l hand 11% to 19 mmol H2/l h and 70%, respectively, as the agitation speed increased from 300rpm to 900 rpm. With increasing the CO loading rate, the volumetric H2 production rateincreased but the extent of CO conversion decreased gradually. The maximal volumetric H2production rate was estimated to be 41 mmol H2/l h, which is nine-fold or fourteen-foldhigher than those reported for photosynthetic bacteria, Rhodospirillum rubrum andRubrivivax gelatinosus, respectively. This is mainly attributed to the ability of P4 to grow to ahigh cell density with a high specific H2 production activity. This study indicates that P4 hasan outstanding potential for a continuous H2 production via water-gas shift reaction once aproper bioreactor system to give a high rate of gas-liquid mass transfer is developed.