The highest organic matter removal and biogas production (VS removal of 77%, TCOD removal of
65.5%, methane production rate of 1422.50 mL CH4/(L d), CH4 content of 68.24%, CH4 yield of
316.11 mL CH4/g CODremoved) was achieved when FWW mixing ratio was 75%. Quantitative real-time
PCR results indicated that the populations of methanogenic archaea were highest when FWW mixing
ratio was 75%. Pyrosequencing analysis revealed relatively high abundances of two methanogenic genera
Methanothermobacter (order Methanobacteriales) and Methanosarcina (order Methanosarcinales) throughout
digestion. The changes of key methanogenic archaea correlate with organic matter removal and biogas
production, and are influenced strongly by organic acid concentration.