Hydrogen Production from Malate or Glycerol By Purple Non-Sulfur Photosynthetic Bacteria

Replacement of fossil fuels with alternative fuels is imperative to counteract climate change and fossil fuel depletion. Molecular hydrogen (H2) is an attractive energy carrier as it does not contain carbon and does not produce harmful byproducts when utilized as a fuel. Hydrogen production of two species of photosynthetic non-sulfur purple bacteria, Rubrivivax gelatinosus and Rhodospirillum rubrum, were studied with malic acid or glycerol as sole carbon source under illumination in anoxygenic conditions. The results in test tubes showed that the maximal hydrogen photoproduction rate (196 mL/g DW/hour) by R. rubrum was obtained under 10% concentration of malic acid in the medium. For R. gelatinosus maximum hydrogen photoproduction rate (108 mL/g DW/hour) was observed in the presence of 10% malic acid in small scale test tubes. For the pilot scale of our study we selected R. rubrum with 10% malic acid to grow in a 17 L photobioreactor that was under artificial illumination with agitation by paddle stirring at 50 RPM. Bacterial growth was shown as an increase in the optical density. During the period of agitation of bacterial culture, there was no visible production of H2. The agitation prevented hydrogen produced from being release from solution to the gas phase of the photobioreactor. The data suggested that it is possible to produce hydrogen by photosynthetic bacteria with inexpensive carbon sources such as malic acid in a pilot scale photobioreactor with additional energy savings (no agitation).