Influence of terminal electron acceptor availability to the anodic oxidation on the electrogenic activity of microbial fuel cell (MFC) S. Srikanth, S. Venkata Mohan ⇑ Bioengineering and Environmental Centre (BEEC), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 607, India highlights " Performance of MFC was evaluated with the function of anode placement from TEA. " Shorter anode distances from TEA showed higher electrogenesis over longer distances. " Anode placement at 3 cm distance from TEA showed higher MFC performance. " Lower conversion efficiency was observed at longer distances due to electron losses. " Voltammetric and bio-electro kinetic studies supported the impact of anode placement. article info Article history: Received 14 June 2012 Received in revised form 11 July 2012 Accepted 14 July 2012 Available online 22 July 2012 Keywords: Bio-electrochemical system (BES) Tafel slopes Wastewater treatment Exchange current density Electron transfer co-efficient abstract The electrogenic activity of microbial fuel cell (MFC) with the function of anode placement from the ter- minal electron acceptor (TEA) was evaluated. Shorter anode distances from TEA showed higher electro- genesis due to the feasibility of higher electron acceptance as well as their discharge towards TEA. Substrate degradation was also higher at shorter anode placements from TEA due to the optimum sub- strate availability to the anodic biofilm. Bio-electro kinetics showed significant variation in the catalytic currents and exchange current densities with the function of anode placement indicating its role in elec- tron acceptance and their transfer to the cathode. Anode placement of 3 cm showed higher electrogenesis (406.38 mW/m 2 ) and substrate degradation (63.12%) along with significantly reduced polarization (6.72 O) and charge transfer resistances compared to other anodic placements. The spacing between elec- trodes is crucial in accepting electrons as well as their discharge towards TEA which ultimately governs the power generation efficacy. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Microbial fuel cell (MFC)/bio-electrochemical system (BES) is a biologically catalyzed electrochemical system which can directly convert the chemical energy to electrical energy through a cascade of redox reactions in the absence of oxygen (Kim et al., 2005; Liu et al., 2005; Cheng et al., 2006; Lowy et al., 2006; Venkata Mohan et al., 2008a–c; Fornero et al., 2010; Oh et al., 2010; Zhong et al., 2011; Kim et al., 2012). Various physical, chemical and operational parameters influence the performance of MFC with respect to power generation and substrate removal. Electrodes-membrane assembly, characteristics of the carbon source, nature of electrode materials, mediators, electrolytic solution, inoculum (biocatalyst) used in anode chamber, operating conditions such as substrate loading rate, pH, temperature and retention time are considered to be some of the important factors which govern the overall effi- ciency of MFC performance (Park and Zeikus, 2003; Gil et al., 2003; Schroder et al., 2003; You et al., 2008; Venkata Mohan et al., 2008b, d, e and 2009; Lefebvre et al., 2011; Srikanth et al., 2010, 2011). In electrode-membrane assembly, placement of electrodes will have a significant influence on proton-electron mobility associated with the power generation potential of MFC (Liu et al., 2005; Cheng et al., 2006; Srikanth et al., 2011; Venkata Mohan and Chandrase- khar, 2011). Considering the role of a charge carrier, a shorter dif- fusion length is believed to give faster electrochemical reaction due to the shorter diffusion time (Liu et al., 2005; Sunga and Choi, 2007). Maximum power output can be obtained by reducing the electrode spacing due to the consequence of reduced internal resis- tance (Liu et al., 2005; Cheng et al., 2006). However, the placement of electrodes by smallest possible electrode spacing was reported to yield less power (Cheng et al., 2006). Therefore, an optimum spacing is required between anode and cathode for a systems using oxygen as the terminal electron acceptor to enhance the electron acceptance from all over the reactor and to decrease the activation losses. Henceforth, an attempt was made in this communication to 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.07.049 ⇑ Corresponding author. Tel.: +91 40 27191664. E-mail address: vmohan_s@yahoo.com (S. Venkata Mohan). Bioresource Technology 123 (2012) 480–487 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech