Electromethanogenesis at medium-low temperatures: Impact on performance and sources of variability

In this study we aimed to understand the impact of medium–low temperatures on the two main steps that usually comprise the electromethanogenesis (EM) process: electrothrophic hydrogenesis and hydrogenothrophic methanogenesis. Results revealed that pure CO2 could effectively be converted into a high-purity biogas (∼90:10 CH4/CO2) at 30 °C. However, when temperature was reduced to 15 °C, methane richness greatly decreased (∼40:60 CH4/CO2). This deterioration in performance was mostly attributed to a decline in methanogenic activity (represented mainly by Methanobacterium and Methanobrevibacter). In contrast, the hydrogenic activity (mostly Desulfomicrobium) did not suffer any significant decay. Results also seemed to indicate that methanogenesis, rather than hydrogenesis, is the main source of variability in EM. Increasing the temperature again to 30 °C restored previous performance, which highlights the resilience of EM to wide temperature fluctuations (from 30 to 15 and back 30 °C).