Hydrogen photoproduction by nutrient‐deprived Chlamydomonas reinhardtii cells immobilized within thin alginate films under aerobic and anaerobic conditions

A new technique for immobilizing H 2 ‐photoproducing green algae within a thin (<400 µm) alginate film has been developed. Alginate films with entrapped sulfur/phosphorus‐deprived Chlamydomonas reinhardtii , strain cc124, cells demonstrate (a) higher cell density (up to 2,000 µg Chl mL −1 of matrix), (b) kinetics of H 2 photoproduction similar to sulfur‐deprived suspension cultures, (c) higher specific rates (up to 12.5 µmol mg −1  Chl h −1 ) of H 2 evolution, (d) light conversion efficiencies to H 2 of over 1% and (e) unexpectedly high resistance of the H 2 ‐photoproducing system to inactivation by atmospheric O 2 . The algal cells, entrapped in alginate and then placed in vials containing 21% O 2 in the headspace, evolved up to 67% of the H 2 gas produced under anaerobic conditions. The results indicate that the lower susceptibility of the immobilized algal H 2 ‐producing system to inactivation by O 2 depends on two factors: (a) the presence of acetate in the medium, which supports higher rates of respiration and (b) the capability of the alginate polymer itself to effectively separate the entrapped cells from O 2 in the liquid and headspace and restrict O 2 diffusion into the matrix. The strategy presented for immobilizing algal cells within thin polymeric matrices shows the potential for scale‐up and possible future applications. Biotechnol. Bioeng. 2008. Biotechnol. Bioeng. 2009;102: 50–58. © 2008 Wiley Periodicals, Inc.