Adaptation of the anaerobic microbiome for in-situ power-to-CH4 processes through fuzzy logic control of H2 input

This study presents the first application of fuzzy logic control (FLC) for regulating in-situ biological methanation via H 2 injection in a fixed-bed reactor. Given the role of CH 4 as a storable and infrastructure-compatible energy carrier, the aim was to improve CH 4 production by dynamically adapting the H 2 supply to the metabolic capacity of the microbiome. This will pave the way for the biological utilisation and storage of renewable H 2 . Over a 226-day operational period, H 2 input was gradually increased based on real-time headspace gas measurements. Coupling the gradual increase in H 2 supply with real-time gas composition data allowed the microbiome to adapt dynamically to changing process conditions. This approach led to a 49 % increase in CH 4 concentration, from 58.4 % to 87.0 %, and improved H 2 conversion rates from 98.2 % to 99.0 %. Chemical analyses of COD, organic acids and nitrogen were performed, as well as taxonomic analyses using 16S rRNA sequencing, and multivariate methods were applied to confirm the adaptation of the microbiome to the FLC H 2 injection. The adopted microbial community was dominated by strictly hydrogenotrophic methanogens, Methanoculleus and Methanobacterium , while increased abundances of Petrimonas , Rectinema , Syntrophomonas , and Geobacter indicate interspecies H 2 transfer and syntrophic cooperation enhancing methanogenesis. These findings demonstrate that FLC-based H 2 control enables dynamic adjustment of in-situ methanation, optimising the interaction between hydrogenogenic, fermentative, syntrophic acetate-oxidising, and hydrogenotrophic microorganisms. This work introduces an adaptive control strategy that supports stable and efficient bio-CH 4 production and represents a significant advance in the field of power-to-gas technologies. • Investigation of in-situ methanation with FLC of H 2 feed in a fixed bed reactor • Achieving a H 2 conversion rate of 99 % and a CH 4 content of 87 % • Observation of a dynamic microbiome adaptation via fuzzy logic-controlled H 2 supply • Establishment of a syntrophic acetate oxidising and hydrogenotrophic microbiome