The decrease in CH4 production may be due to the utilization of metabolic H2 by acetogenic bacteria
to produce acetate.
Acetogenic bacteria belonging to genera Syntrophomonas and Syntrophobacter  convert the acid phase products into acetates (2) and hydrogen.
The result revealed the domination of hydrolytic and fermentative phyla in digester with no digestate recirculation, while syntrophic acetogenic bacteria dominated the digester with recirculation.
Temperature characteristics of methanogenic archaea and acetogenic bacteria
isolated from cold environments.
In an anaerobic system, the acetogenic bacteria
convert organic matter to organic acids, possibly decreasing the pH, reducing the methane production rate and the overall anaerobic digestion process unless the acids were quickly consumed by the methanogens.
Unlike methanogens, acetogenic bacteria
convert [CO.sub.2] and [H.sub.2] to acetate ([CH.sub.3]COOH) rather than to methane.
4 out of 5 hydrolytic, 3 out of 5 acidogenic, and 5 out of 8 acetogenic microorganisms were detected from SWs, while RBs showed the least detected bacteria (2 out of 5 hydrolytic, 1 out of 5 acidogenic, and 2 out of 8 acetogenic bacteria).
Acetogenic bacteria have important role for oxidizing products from acidogenesis and providing appropriate substrate for methanogens.