Isolation of hydrogen-producing bacteria from granular sludge of an upflow anaerobic sludge blanket reactor

Abstract

H-2-producing bacteria were isolated from anaerobic granular sludge. Out of 72 colonies (36 grown under aerobic conditions and 36 under anaerobic conditions) arbitrarily chosen from the agar plate cultures of a suspended sludge, 34 colonies (15 under aerobic conditions and 19 under anaerobic conditions) produced H-2 under anaerobic conditions. Based on various biochemical tests and microscopic observations, they were classified into 13 groups and tentatively identified as follows: From aerobic isolates, Aeromonas spp. (7 strains), Pseudomonas spp. (3 strains), and Vibrio spp. (5 strains); from anaerobic isolates, Actinomyces spp. (11 strains), Clostridium spp. (7 strains), and Porphyromonas sp. When glucose was used as the carbon substrate, all isolates showed a similar cell density and a H-2 production yield in the batch cultivations after 12 h (2.24 - 2.74 OD at 600 nm and 1.02-1.22 mol H-2/mol glucose, respectively). The major fermentation by-products were ethanol and acetate for the aerobic isolates, and ethanol, acetate and propionate for the anaerobic isolates. This study demonstrated that several H-2 producers in an anaerobic granular sludge exist in large proportions and their performance in terms of H-2 production is quite similar.