Microbial Resource Management for Ex Situ Biomethanation of Hydrogen at Alkaline pH

• Main Authors: Washington Logroño, Denny Popp, Sabine Kleinsteuber, Heike Sträuber, Hauke Harms, Marcell Nikolausz
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Microorganisms
• Subjects: power-to-gas; energy storage; biogas upgrading; biomethane; formate; hydrogenotrophic methanogenesis
• Online Access: https://www.mdpi.com/2076-2607/8/4/614

Biomethanation is a promising solution to convert H₂ (produced from surplus electricity) and CO₂ to CH₄ by using hydrogenotrophic methanogens. In ex situ biomethanation with mixed cultures, homoacetogens and methanogens compete for H₂/CO₂. We enriched a hydrogenotrophic microbiota on CO₂ and H₂ as sole carbon and energy sources, respectively, to investigate these competing reactions. The microbial community structure and dynamics of bacteria and methanogenic archaea were evaluated through 16S rRNA and <i>mcrA</i> gene amplicon sequencing, respectively. Hydrogenotrophic methanogens and homoacetogens were enriched, as acetate was concomitantly produced alongside CH₄. By controlling the media composition, especially changing the reducing agent, the formation of acetate was lowered and grid quality CH₄ (≥97%) was obtained. Formate was identified as an intermediate that was produced and consumed during the bioprocess. Stirring intensities ≥ 1000 rpm were detrimental, probably due to shear force stress. The predominating methanogens belonged to the genera <i>Methanobacterium</i> and <i>Methanoculleus</i>. The bacterial community was dominated by <i>Lutispora</i>. The methanogenic community was stable, whereas the bacterial community was more dynamic. Our results suggest that hydrogenotrophic communities can be steered towards the selective production of CH₄ from H₂/CO₂ by adapting the media composition, the reducing agent and the stirring intensity.