Characteristics of continuous hydrogen production and fatty acid formation by an active hydrogen-producing anaerobic bacterium, Clostridium butyricum strain SC-El, was examined under vacuum and non-vacuum culture systems. The continuous cultures were performed using 1040 ml anaerobic glass bottles containing 600 ml of medium including glucose and polypeptone at a concentration of 0.5 or 1.0% as substrate, and were conducted at pH 6.7, hydraulic retention time (HRT) 8h, and 30 degrees C on a reciprocal shaker. The nonvacuum cultures at 16 days of incubation showed 2.0 to 2.3 mol-H-2/mol-glucose and 1.4 to 2.0 mol-H-2/mol-glucose of hydrogen productivity at 0.5 and 1.0% of substrate concentration, respectively. The vacuum cultures conducted at 0.28 atm gave 1.8 to 2.3 mol-H-2/mol-glucose and 1.3 to 2.2 mol-H-2/mol-glucose of hydrogen productivity at 0.5 and 1.0% of substrate concentration, respectively. The fatty acid production from the vacuum cultures exhibited approximately the same yield of fatty acids as those of the non-vacuum cultures. It was concluded that the maximal hydrogen production potential by anaerobic bacteria is 1.3 to 2.2 mol-H-2/mol-glucose, which is less than 50% of theoretical. In addition, the total hydrogen production rate by a two-stage bioreactor consisting of a 1-litre anaerobic fermenter (HRT 10h) and a 4-litre photobioreactor (HRT 36h) feeding at 2.4-litre of 1.0% glucose per day was estimated at 1.4 to 5.6 mol-H-2/mol-glucose, which is 12 to 47% theoretical. (C) 1997 IAWQ. Published by Elsevier Science Ltd.
