• renewable energy;
  • light energy bioconversion;
  • nitrogenase


The possibility of hydrogen production by a hydrogenase impaired mutant strain of Anabaena variabilis in outdoor culture was studied. A computer-controlled rooftop (outdoor) tubular photobioreactor (4.35 L) was assembled. H2 production rates by A. variabilis PK84 grown in CO2 + air in the photobioreactor were measured together with other parameters such as temperature, irradiance, pH, dry biomass weight, and pO2, and Chl a concentrations during summer months of 1998 and 1999. Efficiencies of light energy bioconversion to H2 energy and energy accumulated in biomass were calculated. The influence of irradiance, temperature, and mode of cultivation on H2 production and efficiency of light energy bioconversion were evaluated. The culture produced up to 1.1 L H2 day−1 PhBR−1. The efficiency of light energy to H2 energy bioconversion on some days was 0.094%. However, the conditions for maximum H2 photoproduction and for maximum efficiency of light energy to H2 energy bioconversion were not the same. A. variabilis PK84 could produce hydrogen for prolonged periods (up to 40 days) without injection of fresh inoculum. During this period photobioreactor produced 24.5 L of H2. Possibilities for increasing the efficiency of light energy conversion are discussed. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 777–783, 2002.