Figure 4: The current density of the MFCs during operation. (MFC-1: cathode 1 treated in citrate buffer (pH 3.0), MFC-2: cathode 2 treated in acetate buffer (pH 4.0), MFC-3: cathode 3 treated in MES buffer (pH 5.5), MFC-4: cathode 4 not treated, MFC-5: cathode 5 not treated, MFC-6: cathode 6 not treated).