Terminal steps in the anaerobic digestion of municipal sewage sludge: Effects of inhibitors of methanogenesis and sulfate reduction.

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Abstract
Anaerobic digestion of sewage sludge of municipal wastewater was investigated using inhibitors to determine the relationship between methanogenesis and sulfate reduction. During anaerobic incubation of the sludge without inhibitors, CH4 was actively produced, and there were no volatile fatty acids, the intermediary products of anaerobic degradation of organic matter, in the sludge. Inhibition of methanogenesis by chloroform resulted in the accumulation of H2 and volatile fatty acids such as acetate and propionate. Adding sulfate to the sludge did not affect Ch4 production, but there was much sulfate reduction. In the sulfate-supplemented sludge, the inhibition of methanogenesis also caused acetate accumulation, but not the longer-chain fatty acids or H2. Inhibition of sulfate reduction by molybdate did not affect either CH4 production or the concentrations of the intermediary products. But the inhibition of both methanogenesis and sulfate reduction caused the accumulation of acetate, longer-chain fatty acids and H2. These results indicate that the enhancement of sulfate reduction in the sludge is supported by the acceleration of electron flow in the ecosystem and apparently does not retard methanogenesis.