Hydrogen as clean fuel via continuous fermentation by anaerobic photosynthetic bacteria, Rhodospirillum rubrum

Abstract

Hydrogen has been considered a potential fuel for the future since it is carbon-free and oxidized to water as a combustion product. Bioconversion of synthesis gas to hydrogen was demonstrated in a continuous fermentation utilizing malate as a carbon source. Rhodospirillum rubrum, an anaerobic photosynthetic bacterium catalyzed water gas shift reaction which was used in this research. The synthesis gas (CO) was used as a source of energy along with tungsten light supplied for growth and bioconversion of the photosynthetic bacteria. The microbial process in fermentation media was carried out in continuous culture to observe the effect of light intensity, agitation and liquid dilution rate on hydrogen production. The maximum hydrogen yield at 500 rpm was 0.65 mmol H₂/mmol CO. Desired media flow rate was preferable for high hydrogen production. At 0.65 ml/min media, hydrogen was produced at 7.2 mmol/h. This new approach, use of biocatalyst, can be considered as an alternative method to the conventional Fischer Tropsch synthetic reactions, which were able to convert synthesis gas into hydrogen.

Key Words: Hydrogen, syngas, continuous bioreactor, Rhodospirillum rubrum, light intensity, agitation rate and flow rate.

African Journal of Biotechnology Vol.3(10) 2004: 503-507