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Advancing the application of bioelectrochemical systems necessitates the comprehensive understanding of electron transfer process in electrode-associated biofilm. While in situ electrical measurement by using the split electrode can illustrate the electron conduction in biofilm, the accuracy and interpretation of the obtained data is still in debate. Here, conductance of Geobacter sulfurreducens biofilm is measured by using the split electrode as substrate concentration is changed. Biofilm conductance decreases with the current production as the consumption of substrate. In addition, the measured conductance increases with the area of drain electrode (13.8 ± 1.8 μS for 0.5 cm2 and 29.4 ± 4.2 μS for 1 cm2). These results suggest the measured conductance of biofilm is influenced by microbial metabolism. This effect will diminish when the measurement is performed by using electrochemical impedance spectroscopy or under non-turnover condition. Our results provide the insight on the electrochemical origin of biofilm conductance determined by the in situ electrical measurement. • Biofilm conductance decreased with current production as consumption of substrate. • Biofilm conductance increased with the area of drain electrode. • The measurement of biofilm conductance was influenced by microbial metabolism. • Biofilm conductance significantly decreased under non-turnover condition. [ABSTRACT FROM AUTHOR]

Revealing the pathways of electron transport within electrochemically active biofilms (EABs) is of great importance. Here, mixed-culture EABs are grown on three interdigitated microelectrode arrays (IDAs) with different gap widths of 10 μm, 20 μm and 50 μm and their conductances are determined. The maximum conductive current increases with the decrease of the gap width and charge transfer resistance obtained for the biofilm attaching on the electrode is 3–11 fold less than that for biofilm bridging gaps, suggesting high conductance of biofilm closer to the electrode surface. Results from Raman analysis show high abundance of multi-heme cytochromes in biofilm bridging 10 μm gap, leading to small resistance of biofilm growing on the IDA with 10 μm gap. In addition, the maximum conductive current of biofilm bridging gaps at the potential of −0.40 V vs. Ag/AgCl suggests that electron transfer in biofilm growing on IDAs is redox driven. All these results indicate the spatial heterogeneity of electron transport processes acting within biofilm. Biofilm conductance decreased with the increase of gap's width. Small resistance was found for biofilm adjacent to the electrode surface. Biofilm conductance was depended the abundance of multi-heme cytochrome. The process of electron transfer with EABs was spatial heterogeneous. Panpan Liu: Conducting a research and investigation process, writing the initial draft [ABSTRACT FROM AUTHOR]