Hydrogen production by immobilised Rhodopseudomonas palustris in two photobioreactor configurations

In this study, the phototrophic bacterium, Rhodopseudomonas palustris was immobilised at differing cell densities in transparent, chemically and mechanically resistant, biocompatible polyvinyl alcohol-based hydrogels and employed in photobioreactors to produce hydrogen. The novel PVA-based hydrogels developed and employed in this study were formed under ambient conditions, without the need for toxic gelation inducers, harsh gelation conditions or costly intermediates. In a novel application, these immobilised biocatalysts were employed in continuously stirred photobioreactors, designed to determine the system specific optimal biomass and hydrogel loading for hydrogen production. These results were expanded into the application of the immobilised cells in tubular photobioreactors. In this system, the immobilized bacteria acting as biocatalysts effectively converted the glycerol substrate to high purity (>90% purity) hydrogen, exhibiting a glycerol to hydrogen conversion of 75 ± 15% with a volumetric production rate of 6.84 ± 0.1 mL_H2/L/h and a specific production rate equal to 16.2 ± 0.2 mL_H2/g_CDW/h. This work demonstrates the possibility of using immobilised cells to produce high purity hydrogen, using a waste stream as a substrate.