Characterizing electron transport resistances from anode-respiring bacteria using electrochemical techniques

Characterizing electron transport resistances from anode-respiring bacteria using electrochemical techniques Characterizing electron transport resistances from anode-respiring bacteria using electrochemical techniques Anode-respiring bacteria (ARB) are unique in their capacity to transfer electrons from organic substrates to a solid anode. The result of anode respiration is an electrical current that can be used for various bioenergy applications in microbial electrochemical cells (MXCs), including power generation (Kim et al., 2002), H2 gas production (Liu et al., 2005), reduction of oxidized contaminants (Tandukar et al., 2009), and organic chemical production (Nevin et al., 2010). Thus, MXCs possess the versatility and potential to become a key technology in the bioenergy and waste treatment industries (Logan et al., 2006; Rittmann et al., 2008). An efficient MXC is one that minimizes its resistances to electron and ionic current. These resistances can be present in the anode, the cathode, or the electrolyte. At the cathode, activation or mass transport resistances can impede the flow of electrons to the terminal electron acceptor (e.g., oxygen). In the electrolyte, the flow of ions through water (or an ion exchange membrane) creates an Ohmic resistance known to limit electron flow in MXCs (Logan et al., 2006; Clauwaert et al., 2008). Cathode and electrolyte resistances are well characterized, as they mimic those present in chemical fuel cells (Fan et al., 2008; Borole et al., 2010). However, anode resistances are specific to MXCs, as the ARB metabolic machinery defines the complexity of the resistances and, hence, potential losses involved in anode respiration. Anode resistances can be categorized as those associated with (1) mass transport (Lee et al., 2009), (2) ARB intracellular metabolism (Torres et al., 2008a; Torres et al., 2010), and (3) extracellular electron transfer (EET, Richter et al., 2009; El-Naggar et al., 2008; Manklavar et al., 2011). Figure 1 shows a schematic of how potential losses due to anodic resistances occur within the ARB biofilm. The donor potential (Edonor) represents the most reduced potential present at the anode. The anodic resistances categorized above cause a total anod