Real-time monitoring of biofilm thickness allows for determination of acetate limitations in bio-anodes

Several studies have reported that current produced by electro-active bacteria (EAB) is dependent on anode potential and substrate concentration. However, information about the relation between biofilm growth and current density is scarce. In this study, biofilm thickness was monitored in-situ and this relation explored at three anode potentials and three acetate concentrations. The highest current densities of 3.7 A·m⁻² were obtained for biofilms thinner than 40 μm, even though thicknesses up to 88 μm were measured. Fick's law was used to estimate the acetate penetration depth in the biofilm, acetate diffusion rates in the biofilm, and specific acetate utilization rates. A maximum biofilm thickness of a non-acetate limited biofilm of 55 μm and an acetate diffusion rate of 2.68 × 10⁻¹⁰ m²·s⁻¹ were estimated at −0.2 V vs Ag/AgCl. The results provide information on the target biofilm thickness for which no acetate limitations occur and provide data for modeling works with bio-anodes.