Fig. 1
MFC schematic and voltage diagram. The upper panel illustrates current flow in the MFC, from the oxidation of methane in the anode via M. acetivorans AA/pES1MAT mcr3 (“M. acetivorans”), Geobacter sp., sludge, and electron carriers such as humic acids, to electron consumption in the cathode. In the anode, (i) methane is converted to acetate, which is secreted, by M. acetivorans AA/pES1MAT mcr3. Next, (ii) electrons are produced from acetate by Geobacter sp. (iii). These electrons are transferred to the carbon brush electrode by electron carriers. Electrons are moved to the cathode through a voltmeter and external resistance (1000 Ω) and (iv) consumed by [Fe(CN)6]3−. The lower panel illustrates the voltage (potential energy) for each reaction (adapted from Nagatsu et al. [36]) The first potential band (left end) is for the conversion of methane and electron production reaction by M. acetivorans AA/pES1MAT mcr3. The second potential band is for the electron production reaction from acetate by Geobacter sp. These two reactions have bacterial metabolic losses. The third potential band is for the step provided by the sludge and its electron carriers. The last potential band (right end) is for electron consumption by [Fe(CN)6]3−. There is an activation or concentration loss in proceeding through the each reaction. The y-axis of this panel is arbitrary