Partition of electrons between methanogenesis and sulfate reduction in the anaerobic digestion of animal waste.

Abstract

The partitioning of electrons between methanogenesis and sulfate reduction in various conditions of anaerobic digestion of animal waste was calculated. Even in the presence of rather high concentrations of sulfate, methanogenesis was not suppressed much by sulfate reduction and under certain conditions almost the same amount of methane was produced irrespective of the presence or absence of sulfate. In the presence of rather high concentrations of propionate, sulfate was reduced depending strongly on propionate oxidation, and the total amount of electrons consumed by both methanogenesis and sulfate reduction was increased significantly by the sulfate reduction. When the concentration of propionate was low or nil, there were 2 types of partition of electrons. In one type, sulfate reduction achieved some reducing power by itself and the total amount of electrons consumed by both methanogenesis and sulfate reduction was increased somewhat by sulfate reduction. In the other type, sulfate reduction had no reducing power by itself and competitively inhibited methanogenesis. In the anaerobic digestion of animal waste, sulfate reduction may act mainly as a decomposes of intermediates of anaerobic digestion other than acetate, perhaps mainly propionate, and thus it stimulates the electron flow in the ecosystem.