Hydrogen production, methanogen inhibition and microbial community structures in psychrophilic single-chamber microbial electrolysis cells

Hydrogen production by fermentative bacteria and photosynthetic organisms is depressed under psychrophilic conditions. Here we describe single-chamber microbial electrolysis cells (MECs), which were enriched successfully at 4 °C or 9 °C and operated at these temperatures for the production of hydrogen. The rates of hydrogen production varied from 0.23 ± 0.03 to 0.53 ± 0.04 m³ H₂ m^-3 d^-1, and the hydrogen yield was in the range 2.66 ± 0.22 - 2.94 ± 0.02 mol H₂ mol^-1 acetate. The energy efficiency based on electrical input ranged from 154 ± 9 to 200 ± 18% using an applied voltage of 0.6 V or 0.8 V; CH₄ was not detected in any of the reactors. The separate MECs were first operated at 25 °C and methanogenesis was found to occur in them, however no CH₄ was produced if the cells were operated at 4 °C or 9 °C. 16S rRNA gene clone libraries constructed for Archaea proved that the growth of hydrogenotrophic methanogens such as Methanobrevibacter arboriphilus cultured in MECs at 25 °C was effectively inhibited under psychrophilic conditions, and the growth of these organisms was initially suppressed in these MECs maintained at low temperatures. Bacterial 16S rRNA gene clone library analyses showed that temperature significantly influenced the community structure of the anode biofilms in MECs, and Geobacter psychrophilus was found to be the dominant psychrotolerant population in MECs maintained at 4 °C and 9 °C. Our study also demonstrated that frequent inoculation using pre-acclimatized suspensions of microbial fuel cells (MFCs) greatly facilitated the rapid formation of psychrophilic biofilms in MECs at low temperature.