抄録
In a thermophilically-grown anaerobic sludge consortium acetate degradation can be performed either by acetate splitting reaction by acetate-utilizing methanogens (A-MPB), or by a symbiosis between acetate-oxidizing bacteria (AOB) and hydrogen-utilizing methanogens (H-MPB). The contribution of acetate consumption via hydrogen formation by the symbiosis between AOB and H-MPB was experimentally estimated using a sludge consortium grown in a thermophilic (55°C) UASB reactor operated over 20 months on a mixture of sucrose and volatile fatty acids. Acetate-fed and H2/CO2-fed methanogenic activities of the retained sludge increased with increasing vial-test temperature, exhibiting optima at 65°C.
Acetate degradation vial tests were conducted at 45, 55 and 65°C by varying hydrogen partial pr essure of headspace of individual vials so as to arbitrarily set at different ΔG' values for acetate oxidizing (hydrogen forming) reaction. Acetoclastic cleavage by A-MPB entirely dominated methanogenesis at 45°C At higher temperatures the symbiotic methanogenesis through hydrogen formation became prominent: electron distribution to the symbiotic methanogenesis was accounted for by 42% at 55°C, and 74% at 65°C.These results suggest that the syntrophic association of AOB and H-MPB becomes significant in acetate conversion to methane under thermophilic conditions.
