Hydrogen production by Anabaena cylindrica: effects of varying ammonium and ferric ions, pH, and light

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Abstract
A. cylindrica sparged with Ar gas produced H2 continuously for 30 days under limited light conditions (6.0 W/m2) and for 18 days under elevated light conditions (32 W/m2) in the absence of exogenous N. The efficiency of converting visible light energy (32 W/m2) into chemical energy that is trapped as H2 ranged between 0.35-0.85% (approximately 13 .mu.l of H2/mg [dry wt] per h). Ammonium additions (0.2 mM NH4+) at various times destabilized the system and eventually suppressed H2 production completely, as compared with the control. Cultures grown with 5.0 mg of Fe3+/liter produced H2 at a rate about twice that of cultures with 0.5 mg of Fe3+/liter. Cultures grown at pH 7.4 produced H2 at the same initial rates as cultures that were grown at pH 9.4; the latter cultures continued to produce H2 after CO2 deprivation.

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