Bioelectrochemical analyses of the development of a thermophilic biocathode catalyzing electromethanogenesis

The use of thermophilic microorganisms as biocatalysts for electromethanogenesis was investigated. Single-chamber reactors inoculated with thermophiles and operated at 55 °C showed high CH4 production rates (max. 1103 mmol m(–2) day(–1) at an applied voltage of 0.8 V) with current-capture efficiencies >90%, indicating that thermophiles have high potential as biocatalysts. To improve the electromethanogenic activity, the developed biocathode was transferred to a two-chamber reactor and operated at a poised potential of −0.5 V vs SHE. The CH4 production rates of the biocathode were enhanced approximately 6-fold in 160 h of poised-potential incubation, indicating that the acclimation of the biocathode resulted in performance improvement. Compositional alteration of the cathodic microbiota suggested that a Methanothermobacter-related methanogen and synergistetes- and thermotogae-related bacteria were selected during the acclimation. Cyclic voltammetry of the “acclimated” biocathode showed an augmented cathodic catalytic wave with a midpoint potential at ca. −0.35 V vs SHE. Moreover, the biocathode was able to catalyze electromethanogenesis at −0.35 V vs SHE. These results suggested that the ability of the biocathode to catalyze electromethanogenesis via direct electron transfer was enhanced by the acclimation. This study provides new technological and fundamental information on electromethanogenic bioelectrochemical systems (BESs) that may be extended to other BESs.