Efficient Hydrogen photoproduction by synchronously grown cells of a marine cyanobacterium, Synechococcus sp. Miami BG 043511, under high cell density conditions.

The capability of hydrogen photoproduction under high cell density conditions was examined using synchronously grown cells of nitrogen-fixing Synechococcus sp. Miami BG 043511. Optimum hydrogen yield was obtained when vessels (25 ml) contained 0.2 to 0.3 mg chlorophyll (a) in 3-mL cell suspension. During a 24-h incubation period, an initial phase of hydrogen and carbon dioxide production and a subsequent phase of carbon dioxide uptake and oxygen accumulated as major products after 24 h. after the initial 24-h. After the initial 24-h incubation, as high as 7.4 and 3.7 L (at standard condition) of hydrogen and oxygen, respectively, accumulated in vessels with 22-ml gas phase. This indicated that the pressure in the flask increased to 1.5 atmosphere. Energy conversion efficiency based on photosynthetically active radiation (25 W/m(2)) was about 2.6%. However, increased pressure somehow reduced the duration of hydrogen production. Duration of hydrogen and oxygen production was prolonged by periodical (24-h interval) gas replacement during incubation. (c) 1994 John Wiley & Sons, Inc.