Hydrogen production by cyanobacteria in an automated outdoor photobioreactor under aerobic conditions

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. H 2 production rates by A. variabilis PK84 grown in CO 2 + air in the photobioreactor were measured together with other parameters such as temperature, irradiance, pH, dry biomass weight, and p O 2 , and Chl a concentrations during summer months of 1998 and 1999. Efficiencies of light energy bioconversion to H 2 energy and energy accumulated in biomass were calculated. The influence of irradiance, temperature, and mode of cultivation on H 2 production and efficiency of light energy bioconversion were evaluated. The culture produced up to 1.1 L H 2 day −1 PhBR −1 . The efficiency of light energy to H 2 energy bioconversion on some days was 0.094%. However, the conditions for maximum H 2 photoproduction and for maximum efficiency of light energy to H 2 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 H 2 . Possibilities for increasing the efficiency of light energy conversion are discussed. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 777–783, 2002.