Kinetic experiments for evaluating the nernst-monod model for anode-respiring bacteria (ARB) in a biofilm anode

Anode-respiring bacteria (ARB) are able to transfer electrons from reduced substrates to a solid electrode. Previously, we developed a biofilm model based on the Nernst-Monod equation to describe the anode potential losses of ARB that transfer electrons through a solid conductive matrix. In this work, we develop an experimental setup to demonstrate how well the Nernst-Monod equation is able to represent anode potential losses in an ARB biofilm. We performed low-scan cyclic voltammetry (LSCV) throughout the growth phase of an ARB biofilm on a graphite electrode growing on acetate in continuous mode. The jV response of 9 LSCVs corresponded well to the Nernst-Monod equation, and the half-saturation potential (E_KA) was -0.425 ± 0.002 V vs Ag/AgCl at 30°C (-0.155 ± 0.002 V vs SHE). Anode-potential losses from the potential of acetate reached ∼0.225 V at current density saturation, and this loss was determined by our microbial community's E_KA value. The LSCVs at high current densities showed no significant deviation from the Nernst-Monod ideal shape, indicating that the conductivity of the biofilm matrix (κ_bio) was high enough (≥0.5 mS/cm) that potential loss did not affect the performance of the biofilm anode. Our results confirm the applicability of the Nernst-Monod equation for a conductive biofilm anode and give insights of the processes that dominate anode potential losses in microbial fuel cells.