2.3. Construction and operation conditions of MFCs
In the experiment, dual-chamber type of MFCs were applied.
In every case approx. 107 CFU/mL yeast cell was used to inoculate
the anode chamber. Riboflavin was added to the hopped
wort, as a non-toxic extracellular mediator in concentrations
of 0M, 50M and 100M. Potassium ferrocyianide, 0.1 M,
was used as catholyte in the MFC. The working volume of
anode and cathode chambers was 12mL separately, and they
were separated with proton-exchange membrane (Nafion 117).
Graphite plate, projected surface area of 12 cm2 (smaller size)
and 24 cm2 (larger size), was used as anode in the MFC settings.
Graphite plate was used as cathode in each MFC, having
a projected surface of 24 cm2. The MFCs were operated separately
in batch mode, no pre-inoculation was used. After each
experiment the MFCs were emptied, cleaned and sterilized.
Electrodes were connected to an external resistance (500 )
and parallel connected to a digital multimeter. The generated
voltage on the external resistance was measured. Using Ohm’s
law (I = V/R) the electric current was calculated from the registered
voltage values. The running temperature was 15 ◦C in the
metabolic analysis, in other cases 30 ◦C. The pH of the anode
and cathode chamber was neutral (pH 7.0 ± 0.5). Each experimental
run was carried out simultaneously, in triplicates in three independent MFC units to confirm the reproducibility and reliability of the results.