Hydrogen Production by Immobilized <i>Rhodopseudomonas</i> sp. Cells in Calcium Alginate Beads

The present investigation concerns the potentiality of Rhodopseudomonas sp. cells to produce clean energy such as molecular hydrogen (H2). The abovementioned goal could be reached by improving the capability of purple non-sulfur bacteria to produce H2 via a photofermentative process through the enzyme nitrogenase. Rhodopseudomonas sp. cells were immobilized in calcium alginate gel beads and cultured in a cylindrical photobioreactor at a working volume of 0.22 L. The semi-continuous process, which lasted for 11 days, was interspersed with the washing of the beads with the aim of increasing the H2 production rate. The maximum H2 production rate reached 5.25 ± 0.93 mL/h with a total output of 505 mL. The productivity was 40.9 μL (of H2)/mg (of cells)/h or 10.2 mL (of H2)/L (of culture)/h with a light conversion efficiency of 1.20%