Hydrogen Production by Immobilized Rhodopseudomonas sp. Cells in Calcium Alginate Beads

The present investigation concerns the potentiality of Rhodopseudomonas sp. cells to produce clean energy such as molecular hydrogen (H-2). The abovementioned goal could be reached by improving the capability of purple non-sulfur bacteria to produce H-2 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 H-2 production rate. The maximum H-2 production rate reached 5.25 +/- 0.93 mL/h with a total output of 505 mL. The productivity was 40.9 mu L (of H-2)/mg (of cells)/h or 10.2 mL (of H-2)/L (of culture)/h with a light conversion efficiency of 1.20%.