Biomethanation: Anaerobic fermentation of CO2, H2 and CO to methane

Studies to examine the microbial fermentation of coal gasification products (CO₂, H₂ and CO) to methane have been done with a mixed culture of anaerobic bacteria selected from an anaerobic sewage digestor. The specific rate of methane production at 37°C reached 25 mmol/g cell hr. The stoichiometry for methane production was 4 mmol H₂/mol CO₂. Cell recycle was used to increase the cell concentration from 2.5 to 8.3 g/liter; the volumetric rate of methane production ran from 1.3 to 4 liter/liter hr. The biogasification was also examined at elevated pressure (450 psi) and temperature to facilitate interfacing with a coal gasifier. At 60°C, the specific rate of methane production reached 50 mmol/g cell hr. Carbon monoxide utilization by the mixed culture of anaerobes and by a Rhodopseudomonas species was examined. Both cultures are able to carry out the shift conversion of CO and water to CO₂ and hydrogen.