A mixed anodophilic biofilm exhibits saturation behavior with anodic potential in a microbial fuel cell
Cheng, K.Y., Cord-Ruwisch, R. and Ho, G. (2008) A mixed anodophilic biofilm exhibits saturation behavior with anodic potential in a microbial fuel cell. In: Microbial Fuel Cells First International Symposium, 27 - 29 May, Pennsylvania, USA
Microbial fuel cell (MFC) anodes are insoluble conductive media serving as both the terminal electron acceptor and the physical support for the anodophilic biofilm. Bacterial activity and the power output of a MFC are therefore largely depending on the capacity of the anode to accept electrons from the biofilm. However, our understanding on the bacterial electron transfers in MFC anode is still unclear. Therefore, the aim of this study was to investigate the dependency of the activity of an anodophilic biofilm on the anodic potential in a fed-batch two-chamber computer-controlled MFC. The MFC was operated for over 200 days with acetate as the sole electron donor and ferricyanide as the terminal electron acceptor to establish a highly effective anodophilic biofilm. By controlling the external resistance, steady state microbial activities at various anodic potentials were established at different conditions (e.g. substrate saturating/ starving). Our results suggest the existence of: 1) a critical anodic potential (APcrit.) of ~ -420 mV/AgAgCl, beyond which a more positive anodic potential no longer stimulates bacterial activity and electricity flow; and 2) a half saturation value of anodic potential (~ -455 mV/AgAgCl) at which the anodophilic bacteria produce current at half maximum rate. With the new insight about the relationship between microbial activity and anode potential, operating conditions of MFC could be optimised by controlling or maintaining the anodic potential at the APcrit. level. Further, knowing the actual affinity for the anode and maximum microbial activity in a MFC is expected to help with comparing different biofilms, modeling of MFC processes, or diagnosing MFC malfunctions.
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