Light energy conversion into H2 by Anabaena variabilis mutant PK84 dense cultures exposed to nitrogen limitations

Concentrated cultures (25–86 mg Chl a l - 1 ) of Anabaena variabilis PK84 were incubated under 99% Ar + 1 % CO2 atmosphere in the photobioreactor made of coaxial cylinders. Under illumination equal to 353 μ E m - 2 s - 1 they produced hydrogen with the rate more than 20 ml l - 1 h - 1 for several days. The efficiency of light energy conversion into H2 was approx. 1% and did not depend significantly on initial Chl a concentration. H2/O2 ratio reached 41.5% of theoretical value for water photolysis. Data indicate that dense cultures might be used for outdoor systems under direct sun light. Supra-optimal temperatures 36 ∘ C were not harmful for cultures even for 2 days period. Short-term incubation of cultures under 36 ∘ C even increased H2 production rate and efficiency of light energy bioconversion by 1.25 times.