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The impacts of feeding ratio and loading rate on the microbial community during co-digestion of grass silage with cow manure in an anaerobic laboratory continuously stirred tank reactor were investigated by 16S rRNA gene-based fingerprints. The microbial community remained stable when the reactor was fed with cow manure alone and with up to 20% of grass silage in feedstock at an organic loading rate (OLR) of 2 kg VS m(-3) day(-1). Large changes in the bacterial community were observed when the loading ratio of grass was increased to 40%, while there was little change in the archaeal community. During the increase in OLR from 2 to 4 kg VS m(-3) day(-1) the bacterial community structure showed few differences, whereas Archaea was undetectable. Sequencing of the major DGGE bands indicated that the phylum Bacteriodetes predominated in the bacterial community. Two unclassified bacteria with high abundance survived throughout the operation of the reactor.

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Fermentations can be used to produce sustainable energy carriers, such as hydrogen and ethanol (EtOH), from biomass or organic waste materials. The aim of this research was to prospect efficient H 2 -and EtOHproducing thermophilic microorganisms derived from hot spring environments in Iceland. Hydrogen-and EtOHproducing enrichment cultures were obtained from various hot spring samples over a temperature range of 50-78°C. The temperature dependencies for the most promising enrichments were determined with a temperature-gradient incubator. One of the enrichments (33HL) produced 2.10 mol of H 2 /mol of glucose at 59°C. Another enrichment (9HG), dominated by bacteria closely affiliated with Thermoanaerobacter thermohydrosulfuricus, produced 0.68 mol of H 2 /mol of glucose, and 1.21 mol of EtOH/mol of glucose at 78°C. Hydrogen and EtOH production by 9HG was characterized further in a continuous-flow bioreactor at 74°C. The highest H 2 and EtOH yields of 9HG were obtained at pH 6.8 ( 0.3. Lactate production decreased the H 2 and EtOH yields in the continuous-flow bioreactor, and the yields were lower than those obtained in the batch fermentations. In conclusion, the thorough batch screening of Icelandic hot spring samples indicated some promising enrichments for H 2 or H 2 plus EtOH production from carbohydrate materials.

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