Evaluation of ex-situ hydrogen biomethanation at mesophilic and thermophilic temperatures

Abstract

The biogas is seen as a key renewable resource in achieving the targets of countries renewable energy strategies. However, due to the high amount of CO 2 concentration in biogas production, the energy level of biogas decreases, and the use of biogas as an alternative energy source is limited. The hydrogenotrophic methanogenesis process is one of the key technology that capable to convert CO 2 to CH 4 with H 2 biomethanation. In this study the ex-situ hydrogenotrophic methanogenesis under mesophilic and thermophilic conditions and kinetic parameters such as H 2 utilization rates, CH 4 yields and H 2 gas-liquid mass transfer rates were evaluated. The highest CH 4 concentrations were obtained as of 79 and 81% from the mesophilic and thermophilic reactors at H 2 :CO 2 ratio of 4:1. Also, the efficiency of hydrogen utilization ( η H 2 ) increased to 92% and the CH 4 yield ( Y C H 4 ) reached to 0.28 L CH4 /L H2 in thermophilic reactors. • Biological methanation of CO 2 to CH 4 using H 2 as the electron source was investigated. • Thermophilic conditions were quite effective at CH 4 production. • The highest CH 4 production was obtained at 81% at the H 2 :CO 2 ratio of 4:1. • The H 2 gas-liquid mass transfer was higher at a 4:1 stoichiometric ratio.