Quantification of charge carriers and acetate diffusion lengths in intermittent electro-active biofilms using Electrochemical Impedance Spectroscopy

Abstract

Intermittent anode potential regimes have been used to increase the concentration of charge carriers in electro-active biofilms (EABfs). Even though this increased number of carriers is typically correlated to higher current densities, estimating the concentration of charge carriers in EABfs and linking it to measured current density has never been done. In this study, Electrochemical Impedance Spectroscopy (EIS) and Optical Coherence Tomography (OCT) were used to estimate charge carriers and to study mass transfer limitations in intermittently polarized anodic EABfs. Intermittent potential steps of 20, 60, and 300 s were applied and EABf equilibration times were measured. These times were in the order of 10 s and correlated to the diffusion times obtained from EIS. Acetate consumption rates 100 times faster than the diffusion time of acetate into the EABfs were also estimated with EIS, indicating that current was diffusion limited. Using the capacitance and considering the measured volume of EABf, concentrations of charge carriers ranging from 0.05 molcharge carriers m−3EABf at current densities of 1 A m−2 up to 0.2 molcharge carriers m−3EABf at current densities higher than 2 A m−2 were calculated. This study shows that EIS can be used to study developing EABfs in a non-destructive way and in real-time.