Adaptation of anaerobic culture to bioconversion of carbon dioxide with hydrogen to biomethane

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 H2 to biomethane based on the activity of hydrogenotrophic methanogens are also currently being researched. This study deals with the adaptation of anaerobic culture to H2 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 H2 loading rate. Thermophilic conditions were favourable also for homoacetogens producing higher concentration of acetate from CO2 and H2 under thermophilic condition compared to mesophilic condition in the excess of H2. Maximum capacity of the used thermophilic suspended biomass for bioconversion of CO2 was the H2 loading rate 2 L/(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.