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(H_(2)).Immobilization of photosynthetic microorganisms is used for many biotechnological applications such as H_(2) 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 H_(2) production.In this work,the ability of immobilized Rhodopseudomonas sp.S16-VOGS3 cells to produce H_(2) 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 H_(2) with an average H_(2) production rate of 2.99 mL/h.The average productivity was 126.4μL(H_(2))/mg(cells)/h or 14.96 mL(H_(2))/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 H_(2) with an average H_(2) production rate of 1.55 mL/h.The average productivity was 31.1μL(H_(2))/mg(cells)/h or 2.58 mL(H_(2))/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 H_(2) production efficiency.