Bioaugmentation of an electrochemically active strain to enhance the electron discharge of mixed culture: process evaluation through electro-kinetic analysis

Abstract

The functional role of electrochemically active bacteria (EAB), Shewanella haliotis ATCC 49138 as biocatalyst for bioaugmentation onto anodic native microflora (anaerobic) was evaluated to enhance the electrogenic activity of microbial fuel cell (MFC). Fuel cell operation with S. haliotis (MFC-S) alone as anodic biocatalyst showed relatively higher power output (295 mV; 2.13 mA at 100 Ω) than mixed culture (MFC-M; 233 mV; 1.35 mA at 100 Ω) which might be attributed to the higher electron discharge capability of the EAB. Cyclic voltammetry profiles and Tafel slope analysis documented significant variation in bio-electrochemical behaviour and electro-kinetic aspects of fuel cells with the function of anodic biocatalyst. Two-fold higher capacitance and exchange current was observed with MFC-S operation compared to MFC-M. Lower Tafel slope and polarisation resistance observed with MFC-S operation indicated higher electron discharge capability of S. haliotis over the mixed consortia operation. However, the extent of power generation period and substrate degradation efficiency was comparatively higher with mixed culture operation. After augmentation with S. haliotis (MFC-SA), anodic microflora showed rapid enhancement in the fuel cell performance in terms of power output (378 mV; 2.73 mA) and bio-electrochemical behaviour. After augmentation, fifteen-fold higher exchange current density, ten-fold lower electron transfer coefficient and hundred-fold lower polarization resistance was observed compared to MFC-M operation. The syntrophic association of S. haliotis with native anodic biocatalyst showed positive influence on the electron discharge capabilities due to reduction in the activation losses. The stable and high electron discharge pattern observed with augmented system throughout the operation indicates the system stability in current generation.