The microcosm of a biogas fermenter:Comparison of moderate hyperthermophilic(60 deg C) with thermophilic (55 deg C) conditions

摘要

An automated biogas fermenter running continuously for about two years usingfodder and sugar beet silage as mono-substrate without manure addition wasanalyzed simultaneously by amplified ribosomal DNA restriction analysis andmicroscopy. In this long-term fermentation study, an oscillating population ofprokaryotes was observed. The presence of most bacteria expected to be involvedin hydrolysis of biomass via the anaerobic food chain was confirmed. In any casethe methanogen population appeared more stable as it exhibited a lesser degree ofvariability. The more fluctuating population structure of the bacteria might bedue to the fact that most of them were carbohydrate fermenting species whichwere therefore somewhat interchangeable. Hydrogenotrophic methanogens usingH_2 + CO_2 as substrate (Methanobacteriales and Methanomicrobiales) clearlydominated. Therefore, the methanogenesis of energy crops is apparently initiatedby gasification to H_2 + CO_2 followed by the biogasification to CH_4 + CO_2. Acetotrophicmethanogens (Methanosarcinales) represented a minority with aproportion of 10% or less of the methanogenic population (only at 55 deg C). Theacetotrophic Methanosaeta seemed to be completely absent at temperatures of 55or 60 deg C. Pure culture studies established previously that Methanobacteria tolerateat least a sixfold higher ammonium concentration (6000 mg/L) than Methanosaetaand a twofold higher ammonium concentration than Methansarcina. Thisindicates that running industrial scale fermenters at thermophilic instead of thecommon mesophilic conditions might be an effective way to exclude the morestress susceptible (e.g. high concentration of ammonium, H_2S and acetate) acetotrophicmethanogens and therefore improve the reliability of such plants.