Biological hydrogen production by anaerobic mixed communities was studied in batch systems and in continuous-flow bioreactors using sucrose as the substrate. The systems were seeded with anaerobically digested municipal biosolids that had been heat treated at 100°C for 15 minutes. During operation, repeated heat treatments of the biomass in the reactors at 90°C for 20 minutes were performed. Results indicated that both initial heat treatment of the inoculum and repeated heat treatments of the biomass during operation promoted hydrogen production by eliminating non-spore forming hydrogen consuming microorganisms and by selecting for hydrogen producing spore forming bacteria. An operational pH of 5.5 was shown to be optimal for hydrogen production. The conversion efficiency and hydrogen yield were 0.0892 L-H 2 /g-COD and 1.5291 mole of H 2 /mole of sucrose, respectively. Terminal restriction fragment length polymorphism (T-RFLP) analysis showed that Clostridium and Bacillus species were dominant populations in the bioreactors. A positive correlation was observed between the total abundance of Clostridium species and hydrogen production during part of an operational run.

Biological hydrogen production by anaerobic mixed communities was studied in laboratory-scale bioreactors using sucrose as the substrate. A bioreactor in which a fraction of the return sludge was exposed to repeated heat treatments performed better than a control bioreactor without repeated heat treatment of return sludge and produced a yield of 2.15 moles of hydrogen per mole of sucrose, with 50% hydrogen in the biogas. Terminal restriction fragment length polymorphism analysis showed that two different Clostridium groups (comprised of one or more species) were dominant during hydrogen production. The relative abundance of two other non-Clostridium groups increased during periods of decreased hydrogen production. The first group consisted of Bifidobacterium thermophilum, and the second group included one or more of Bacillus, Melissococcus, Spirochaeta, and Spiroplasma spp. Water Environ. Res., 79, 975 (2007).