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

Concentrated cultures (25–86 mg Chl al-1) of Anabaena variabilis   PK84 were incubated under 99% Ar+1%Ar+1% CO2 atmosphere in the photobioreactor made of coaxial cylinders. Under illumination equal to 353μEm-2s-1 they produced hydrogen with the rate more than 20mll-1h-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.