A framework for modeling electroactive microbial biofilms performing direct electron transfer

• A modeling platform for direct electron transfer (DET) biofilms was developed.
• Both constant and dynamic potential conditions can be described.
• Model Geobacter anodes were compared to different experiments.
• The concentration of cytochromes plays a key role for describing experimental data.
• Different shares of cytochrome may be “active” during CA (300 mM) and CV (3 mM).

A modeling platform for microbial electrodes based on electroactive microbial biofilms performing direct electron transfer (DET) is presented. Microbial catabolism and anabolism were coupled with intracellular and extracellular electron transfer, leading to biofilm growth and current generation. The model includes homogeneous electron transfer from cells to a conductive biofilm component, biofilm matrix conduction, and heterogeneous electron transfer to the electrode. Model results for Geobacter based anodes, both at constant electrode potential and in voltammetric (dynamic electrode potential) conditions, were compared to experimental data from different sources. The model can satisfactorily describe microscale (concentration, pH and redox gradients) and macroscale (electric currents, biofilm thickness) properties of Geobacter biofilms. The concentration of electrochemically accessible redox centers, here denominated as cytochromes, involved in the extracellular electron transfer, plays the key role and may differ between constant potential (300 mM) and dynamic potential (3 mM) conditions. Model results also indicate that the homogeneous and heterogeneous electron transfer rates have to be within the same order of magnitude (1.2 s− 1) for reversible extracellular electron transfer.

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