In-situ biogas upgrading with pulse H additions: The relevance of methanogen adaption and inorganic carbon level.

Surplus electricity from fluctuating renewable power sources may be converted to CH via biomethanisation in anaerobic digesters. The reactor performance and response of methanogen population of mixed-culture reactors was assessed during pulsed H injections. Initial H uptake rates increased immediately and linearly during consecutive pulse H injections for all tested injection rates (0.3 to 1.7L/L/d), while novel high throughput mcrA sequencing revealed an increased abundance of specific hydrogenotrophic methanogens. These findings illustrate the adaptability of the methanogen population to H injections and positively affects the implementation of biomethanisation. Acetate accumulated by a 10-fold following injections exceeding a 4:1 H:CO ratio and may act as temporary storage prior to biomethanisation. Daily methane production decreased for headspace CO concentrations below 12% and may indicate a high sensitivity of hydrogenotrophic methanogens to CO limitation. This may ultimately decide the biogas upgrading potential which can be achieved by biomethanisation.