Impact of interfacial charge transfer on the start-up of bioelectrochemical systems

Abstract

In order to increase the efficiency of microbial fuel cells and related bioelectrochemical systems (BESs), one of the common approaches is to lower the resistance of the anode surface to increase the extracellular electron transfer (EET) of anode respiring bacteria (ARB). As our work demonstrates here, this approach is not ideal when dealing with common species of ARB. Bacteria colonized an electrode surface modified with graphite material doped with nonconductive calcium sulfide (CaS) more favorably than the conductive magnetite (Fe3O4) or semiconductive iron (II) sulfide (FeS). Average anodic current densities of 8.2±0.25Am−2 (Fe3O4), 10.7±0.46Am−2 (FeS) and 21.3±1.12Am−2 (CaS) were achieved as compared to that of non-doped activated carbon (5.04±0.12Am−2). Bioelectrochemical evaluation during growth using simple low-scan (1mVs−1) cycle voltammetry (LSCV) indicated variations in patterns which reflect the variability of the ARBs growth. On the other hand, despite the high affinity of bacteria to grow at a faster rate on Fe3O4-anode and CaS-anode, as indicated by the maximum specific growth rate during the start-up exponential phase, the kinetic scan rate study of derivative cycle voltammetry (DCVs) during growth indicated accumulation of bacteria-produced mediators on iron containing anodes which reduced their electrochemical activity. Thus, irrespective of surface resistance, the CaS doped graphite represented a promising anode material which is suitable for highly efficient BES.