Bioelectrical Methane Production with an Ammonium Oxidative Reaction under the No Organic Substance Condition

The present study investigated bioelectrical methane production from CO(2) without organic substances. Even though microbial methane production has been reported at relatively high electric voltages, the amount of voltage required and the organisms contributing to the process currently remain unknown. Methane production using a biocathode was investigated in a microbial electrolysis cell coupled with an NH(4)(+) oxidative reaction at an anode coated with platinum powder under a wide range of applied voltages and anaerobic conditions. A microbial community analysis revealed that methane production simultaneously occurred with biological denitrification at the biocathode. During denitrification, NO(3)(–) was produced by chemical NH(4)(+) oxidation at the anode and was provided to the biocathode chamber. H(2) was produced at the biocathode by the hydrogen-producing bacteria Petrimonas through the acceptance of electrons and protons. The H(2) produced was biologically consumed by hydrogenotrophic methanogens of Methanobacterium and Methanobrevibacter with CO(2) uptake and by hydrogenotrophic denitrifiers of Azonexus. This microbial community suggests that methane is indirectly produced without the use of electrons by methanogens. Furthermore, bioelectrical methane production occurred under experimental conditions even at a very low voltage of 0.05‍ ‍V coupled with NH(4)(+) oxidation, which was thermodynamically feasible.