In-situ biogas upgrading with pulse H2 additions: The relevance of methanogen adaption and inorganic carbon level

Abstract

Surplus electricity from fluctuating renewable power sources may be converted to CH₄ via biomethanisation in anaerobic digesters. The reactor performance and response of methanogen population of mixed-culture reactors was assessed during pulsed H₂ injections. Initial H₂ uptake rates increased immediately and linearly during consecutive pulse H₂ injections for all tested injection rates (0.3 to 1.7L_H2/L_sludge/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 H₂ injections and positively affects the implementation of biomethanisation. Acetate accumulated by a 10-fold following injections exceeding a 4:1 H₂:CO₂ ratio and may act as temporary storage prior to biomethanisation. Daily methane production decreased for headspace CO₂ concentrations below 12% and may indicate a high sensitivity of hydrogenotrophic methanogens to CO₂ limitation. This may ultimately decide the biogas upgrading potential which can be achieved by biomethanisation.

Keywords: Acetate; CO(2) affinity; H(2); Hydrogenotrophic methanogenesis; In situ biogas upgrading.