Photofermentative hydrogen production by immobilized Rhodopseudomonas sp. S16-VOGS3 cells in photobioreactors

One of the most important solutions to overcome energy and environmental problems and to replace the fossil fuel-based economy could be the use of photosynthetic microorganisms. The use of photosynthetic microorganisms is a potential alternative to energy generation from fossil fuels because they efficiently produce hydrogen (H2). Immobilization of photosynthetic microorganisms is used for many biotechnological applications such as H2 production. This method appears attractive because it restricts cell movement in an entrapped matrix. Immobilization of Rhodopseudomonas sp. S16-VOGS3 cells is a promising way to improve H2 production. In this work, the ability of immobilized Rhodopseudomonas sp. S16-VOGS3 cells to produce H2 was investigated in two types of PBRs. The PBRs used in this work were a cylindrical one with 0.2 L working volume (C-PBR) and a flat Roux type with 0.6 L working volume (FRT-PBR). The calcium alginate beads prepared were resistant to culture mixing and showed little leakage of cells, and the immobilized cells continued the photofermentation process in both PBRs. The immobilized cells in the C-PBR produced 936.8 mL of H2 with an average H2 production rate of 2.99 mL/h. The average productivity was 126.4 μL (H2)/mg (cells)/h or 14.96 mL (H2)/L (culture)/h, and the light conversion efficiency was 2.37 %. The immobilized cells in the FRT-PBR produced a total of 662.2 mL of H2 with an average H2 production rate of 1.55 mL/h. The average productivity was 31.1 μL (H2)/mg (cells)/h or 2.58 mL (H2)/L (culture)/h, and the light conversion efficiency was 0.52 %. The more uniform and therefore more efficient degree of bacterial cell mixing achieved in the C-PBR with cylindrical configuration played an important role compared to the FRT-PBR. In the FRT-PBR, the beads were aggregated at the bottom, which limited light penetration and resulted in low H2 production efficiency.