Affinity of microbial fuel cell biofilm for the anodic potential.

In analogy to the well established dependency of microbial reactions on the redox potential of the terminal electron acceptor, the dependency of the microbial activity in a highly active microbial fuel cell on the potential of the electron-accepting electrode (anode) in a microbial fuel cell (MFC) is investigated. An acetate-fed, pH-controlled MFC was operated for over 200 days to establish a highly active MFC anodic biofilm using ferricyanide as the catholyte and granular graphite as electrode material. From the Coulombic efficiency of 83% of the MFC the microbial activity could be recorded by online monitoring of the current. Our results suggest that (1) in analogy to the Michaelis-Menten kinetics a half-saturation anodic potential (here termed k(AP) value) could be established at which the microbial metabolic rate reached half its maximum rate. This k(AP) value was about -455 mV (vs Ag/AgCl) for our acetate-driven MFC and independent of the oxidation capacity of the cathodic half-cell; (2) a critical AP (here termed AP(crit)) of about -420 mV (vs Ag/AgCl) was established that characterizes the bacterial saturation by the electron-accepting system. This critical potential appeared to characterize the maximum power output of the MFC. This information would be useful for modeling and optimization of microbial fuel cells and the relative comparison of different microbial consortia at the anode.