Study of the performance of a thermophilic biological methanation system

This study investigated the operation of ex-situ biological methanation at two thermophilic temperatures (55 °C and 65 °C). Methane composition of 85-88% was obtained and volumetric productivities of 0.45 and 0.4 L CH4/L reactor were observed at 55 °C and 65 °C after 24 h respectively. It is postulated that at 55 °C the process operated as a mixed culture as the residual organic substrates in the starting inoculum were still available. These were consumed prior to the assessment at 65 °C; thus the methanogens were now dependent on gaseous substrates CO2 and H2. The experiment was repeated at 65 °C with fresh inoculum (a mixed culture); methane composition and volumetric productivity of 92% and 0.46 L CH4/L reactor were achieved in 24 h. Methanothermobacter species represent likely and resilient candidates for thermophilic biogas upgrading.