Methane production on thickened, pre-fermented manure

► Anaerobic digestion (AD) of pre-fermented manure generated significant biogas. ► Process stability in the two-stage system was comparable to AD receiving raw manure. ► Two-stage AD stoichiometry was comparable to conventional single stage AD. ► Two-stage AD yielded a larger population of acetoclastic methanogens. Over 9million dairy cows generate an estimated 226billionkg of wet manure annually in the US. The purpose of this study was to demonstrate the viability of a novel two-stage anaerobic digestion (AD) process for producing methane-rich biogas on pre-fermented dairy manure. In summary, it was observed that AD of thickened pre-fermented manure can generate comparable biogas quantities to AD using raw manure, with enhanced methane content. Despite receiving a lower quality (i.e., partially biodegraded) substrate, biogas stoichiometry and overall process stability in the two-stage system was also comparable to AD receiving raw manure. Finally, the two-stage AD was more enriched with the acetoclastic methanogen Methanosarcinaceae (Msc; compared to AD of raw manure) and biogas production appeared closely linked with the Msc fraction. In fact, the enhanced enrichment of Msc likely contributed to the successful and stable operations.