Microbial electrosynthesis of multi-carbon volatile fatty acids under the influence of different imposed potentials

Single chamber microbial electrosynthesis (MES) cells were adapted in this study to evaluate suitable external voltage to enhance the volatile fatty acids (VFAs) generation from CO₂. MES operations with heat-treated sludge was conducted in batch mode under three different applied voltages viz. 0.4 (MES-1), 0.8 (MES-2) and 1.0 V (MES-3). All MESs could produce acetic and iso-butyric acid as main component of VFA; whereas the corresponding maximum VFAs recovery of 8.6 mM and 5.5 mM was noted higher in case of MES-2 followed by MES-3 and MES-1. MES-2 recorded higher average coulombic efficiency of 27.5%, which was found to be 1.4 and 1.2-times higher than MES-1 and MES-3, respectively. The electrochemical analyses further confirmed the superiority of MES-2 over others as the reduction current in cyclic voltammetry of 214 mA was relatively higher with low charge transfer resistance of 100 mΩ. The scanning electron microscopy of the biofilm on the cathode of MES-2 also indicated strong interaction between the electrode framework and electroactive microorganisms. This result suggests that optimized external voltage is needed to obtain maximum valuable chemicals from CO₂ in a single chamber MES, which can be directly applied in field scale systems using renewable sources of energy.