Adaptation of a microbial community to demand-oriented biological methanation

BACKGROUND: Biological conversion of the surplus of renewable electricity and carbon dioxide (CO(2)) from biogas plants to biomethane (CH(4)) could support energy storage and strengthen the power grid. Biological methanation (BM) is linked closely to the activity of biogas-producing Bacteria and methanogenic Archaea. During reactor operations, the microbiome is often subject to various changes, e.g., substrate limitation or pH-shifts, whereby the microorganisms are challenged to adapt to the new conditions. In this study, various process parameters including pH value, CH(4) production rate, conversion yields and final gas composition were monitored for a hydrogenotrophic-adapted microbial community cultivated in a laboratory-scale BM reactor. To investigate the robustness of the BM process regarding power oscillations, the biogas microbiome was exposed to five hydrogen (H(2))-feeding regimes lasting several days. RESULTS: Applying various “on–off” H(2)-feeding regimes, the CH(4) production rate recovered quickly, demonstrating a significant resilience of the microbial community. Analyses of the taxonomic composition of the microbiome revealed a high abundance of the bacterial phyla Firmicutes, Bacteroidota and Thermotogota followed by hydrogenotrophic Archaea of the phylum Methanobacteriota. Homo-acetogenic and heterotrophic fermenting Bacteria formed a complex food web with methanogens. The abundance of the methanogenic Archaea roughly doubled during discontinuous H(2)-feeding, which was related mainly to an increase in acetoclastic Methanothrix species. Results also suggested that Bacteria feeding on methanogens could reduce overall CH(4) production. On the other hand, using inactive biomass as a substrate could support the growth of methanogenic Archaea. During the BM process, the additional production of H(2) by fermenting Bacteria seemed to support the maintenance of hydrogenotrophic methanogens at non-H(2)-feeding phases. Besides the elusive role of Methanothrix during the H(2)-feeding phases, acetate consumption and pH maintenance at the non-feeding phase can be assigned to this species. CONCLUSIONS: Taken together, the high adaptive potential of microbial communities contributes to the robustness of BM processes during discontinuous H(2)-feeding and supports the commercial use of BM processes for energy storage. Discontinuous feeding strategies could be used to enrich methanogenic Archaea during the establishment of a microbial community for BM. Both findings could contribute to design and improve BM processes from lab to pilot scale. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13068-022-02207-w.