Assessing the Utility of Various Buffer Concentrations for Alleviating pH Gradients in Geobacter sulfurreducens Biofilms

In order to optimize the ability of Geobacter sulfurreducens to produce electrical current and remediate wastewater, several physiological challenges must be overcome. The accumulation of protons at the electrode surface of a microbial fuel cell (MFC) decreases the pH, and, thus, the ability of the bacteria to maintain baseline metabolic conditions. To evaluate the extent to which this pH change hinders performance, the buffer concentration supplied to G. sulfurreducens reactors was varied. The resulting biofilms were subjected to chronoamperometry, cyclic voltammetry, and confocal microscopy to determine metabolic function and biofilm thickness. Biofilms grown with a 30-mM bicarbonate buffer experienced limitations on cell function and current output due to proton accumulation, while 90- and 150-mM conditions alleviated these limitations most of the measurements. Based on the current output, estimated biofilm thickness, and the medium-rate and slow-rate scan rate cyclic voltammetry, benefits exist for buffer concentrations greater than 30 mM. If the kinetics of G. sulfurreducens electron transfer are optimized, the potential of the technique to be implemented for energy recovery is improved.