Kinetics and scale up of oxygen reducing cathodic biofilms.

The goals of this work were to study the kinetics and investigate the factors controlling the scale up of oxygen reducing mixed culture cathodic biofilms. Cathodic biofilms were enriched on different electrode sizes (14.5 cm, 40.3 cm, 131 cm and 466 cm). Biofilm enrichment shifted the oxygen reduction onset potential from -0.1 V to 0.3 V, indicating the biofilm catalyzed oxygen reduction. The kinetics of oxygen reduction were studied by varying the bulk dissolved oxygen concentration. Oxygen reduction followed a Michaelis-Menten kinetics on all electrode sizes. The maximum current density decreased with increasing electrode surface area (-97.0 ± 10.6 μA/cm, -76.0 ± 8.2 μA/cm, -66.3 ± 3.0 μA/cm and -43.5 ± 10.5 μA/cm, respectively). Cyclic voltammograms suggest that scale up was limited by ohmic resistance, likely due to the low ionic conductivity in the wastewater medium. Mathematical modeling using combined Michaelis-Menten and Butler-Volmer model supports that the decrease in current density with increasing electrode surface area is caused by ohmic losses. Analysis of the microbial community structure in different size electrodes and in multiple regions on the same electrode showed low variability, suggesting that the microbial community does not control the scale up of cathodic biofilms.