Biogas is composed of energetically useable methane (CH4) ranging from 50 to 70% and carbon dioxide (CO2) taking up 30-50%. To upgrading biogas to biomethane for better exploitation of its energetical potential, many different physico-chemical processes are commercially applied. Besides these methods, biological methods for the conversion of CO2 with electrolytic H-2 to biomethane based on the activity of hydrogenotrophic methanogens are also currently being researched. This study deals with the adaptation of anaerobic culture to H-2 and CO2 as substrates under thermophilic and mesophilic conditions. Thermophilic cultures initially showed slower adaptation, but CO2 conversion efficiency was finally by 12.7% higher compared to the mesophilic culture under the same conditions of the H-2 loading rate. Thermophilic conditions were favourable also for homoacetogens producing higher concentration of acetate from CO2 and H-2 under thermophilic condition compared to mesophilic condition in the excess of H-2. Maximum capacity of the used thermophilic suspended biomass for bioconversion of CO2 was the H-2 loading rate 2L/(L.d) resulting in CO2 bioconversion efficiency of 84% (median) in contrast with 40% (median) for mesophilic culture. The system was limited by the concentration of biomass round 4 g/L. (C) 2019 Published by Elsevier Ltd.