Oxygen traces impact on biological methanation from hydrogen and CO2.

Biomethane production from biological methanation of CO₂ is promising both for biogas upgrading and surplus renewable energy storage. One of the questions for process upscaling is the impact of oxygen (in the biogas or in the purified CO₂-rich off-gas) on the biological process. An adapted anaerobic thermophilic consortium was submitted to increasing amounts of oxygen in batch and continuous tests at partial pressures ranging from 0 to 50 mbar. Oxygen was quickly consumed and hydrogen uptake remained similar. In the same time, methane production dropped (-4 % in continuous tests). Part of the oxygen introduced was reduced biologically by hydrogen. The amount of hydrogen diverted to oxygen reduction (up to 15 % at 50 mbar O₂) was proportional to the oxygen partial pressure. These results suggest that biological methanation systems tolerate the presence of oxygen. However, additional hydrogen should be added to maintain the conversion of CO₂ into methane.