Microbial community composition is consistent across anaerobic digesters processing wheat-based fuel ethanol waste streams

• Manure amendment increased the rate of methane accumulation.
• Manure amendment of thin stillage had a synergistic effect on methane accumulation.
• Bacterial communities had similar structure and composition across digester inputs.
• All reactors were populated by both acetoclastic and hydrogenotrophic methanogens.

Biochemical methane potential (BMP) assays were conducted on byproducts from dry-grind wheat-based ethanol plants amended with feedlot manure at two input ratios. Whole stillage (WST), thin stillage (TST) and wet cake (WCK) were tested alone and with 1:1 and 2:1 ratios (VS basis) of byproduct:feedlot manure in bench-scale batch reactors. The addition of manure increased both the rate and consistency of methane production in triplicate reactors. In addition, digesters co-digesting thin stillage and cattle manure at 1:1 and 2:1 stillage:manure produced 125% and 119% expected methane based on the biomethane potential of each substrate digested individually. Bacterial community analysis using universal target amplification and pyrosequencing indicated there was a numerically dominant core of 42 bacteria that was universally present in the reactors regardless of input material. A smaller-scale analysis of the archaeal community showed that both hydrogenotrophic and acetoclastic methanogens were present in significant quantities.