A framework for modeling electroactive microbial biofilms performing direct electron transfer.

Area of Science:

• Bioelectrochemistry
• Microbial Electrochemistry
• Biofilm Modeling

Background:

• Electroactive microbial biofilms facilitate direct electron transfer (DET) for applications like microbial fuel cells.
• Accurate modeling is essential to understand and optimize biofilm performance in microbial electrochemical technologies.
• Existing models often lack comprehensive integration of intracellular, extracellular, and biofilm matrix electron transfer processes.

Purpose of the Study:

• To develop and present a comprehensive modeling platform for microbial electrodes.
• To couple microbial metabolism, intracellular, and extracellular electron transfer with biofilm growth and current generation.
• To validate the model against experimental data for Geobacter-based anodes under various conditions.

Main Methods:

• Developed a model incorporating homogeneous electron transfer from cells to the biofilm matrix, biofilm matrix conduction, and heterogeneous electron transfer to the electrode.
• Coupled microbial catabolism and anabolism with electron transfer processes to simulate biofilm growth and current output.
• Validated model predictions against experimental data for Geobacter biofilms under constant and dynamic electrode potential conditions.

Main Results:

• The model successfully describes microscale properties (e.g., concentration, pH, redox gradients) and macroscale properties (e.g., current, biofilm thickness) of Geobacter biofilms.
• The concentration of cytochromes (redox centers) is identified as a key factor, with differing optimal values under constant (300 mM) versus dynamic (3 mM) potential.
• Homogeneous and heterogeneous electron transfer rates must be of the same order of magnitude (~1.2 s⁻¹) for efficient extracellular electron transfer.

Conclusions:

• The developed modeling platform provides a robust framework for simulating microbial electrodes.
• The model highlights the critical role of cytochrome concentration and electron transfer kinetics in biofilm performance.
• This work advances the understanding of electron transfer mechanisms in electroactive biofilms, aiding in the design of improved microbial electrochemical systems.