Population dynamics of anaerobic microbial consortia in thermophilic granular sludge in response to feed composition change

A thermophilic UASB reactor was operated at 55 degreesC for greater than 47 0 days in order to investigate the effects of feed composition an the chang es in microbial community structure where thermophilic granular sludge was used as the inoculum source. The feed compositions were changed with cultiv ation days; phase 1. (1-70 days), alcohol distillery wastewater; phase 2 (7 1-281 days), artificial acetate wastewater; phase 3 (282-474 days), artific ial sucrose wastewater. During the first one month of each phase, the metha nogenic activity and cell density of methanogens quantified by fluorescence in situ hybridization (FISH) drastically changed as a result of shift in f eed composition. When artificial acetate wastewater was used as feed, retai ned granular sludge was partially disintegrated due to a decrease in the nu mber of symbiotic bacterial community members: acetogens (acidogens) and hy drogenotrophic methanogens. In contrast, when the feed was shift ed to sucr ose (phase 3), granulation of biomass was promoted by a remarkable prolifer ation of the symbiotic community. The presence of hydrogen-utilizing methan ogens and acetogens (acidogens) are shown to be effective for the enhanceme nt of thermophilic granulation. The cell density of methanogens determined by FISH was strongly correlated with the methane-producing potential of the retained thermophilic granular sludge.