Comparison of electrochemical and microbiological characterization of microbial fuel cells equipped with SPEEK and Nafion membrane electrode assemblies.

Microbial fuel cells equipped with SPEEK-MEA (SPEEK-MFC) and Nafion-MEA (Nafion-MFC) were constructed with organic waste as electron donor and lake sediment as inoculum and were then evaluated comprehensively by electrochemical and microbial analyses. The proton conductivity of SPEEK was several hundreds-fold lower than that of Nafion 117, whereas the oxygen mass and diffusion transfer coefficients of SPEEK were 10-fold lower than those of Nafion 117. It was difficult to predict which was better membrane for MFC based on the feature of membrane. Analyses of polarization curves indicated that the potential of electricity production was similar in both MFCs, as the SPEEK-MFC produced 50-80% of the practical current density generated by the Nafion-MFC. Chronopotentiometry analyses indicated that the Nafion-MEA kept the performance longer than the SPEEK-MEA for long period, whereas performance of both anodes improved on time. Multidimensional scaling analyses based on DGGE profiles revealed the anolytic and biofilm communities of the SPEEK-MFC had developed differently from those of the Nafion-MFC. Clone library analyses indicated that Geobacter spp. represented 6.3% of the biofilm bacterial community in the Nafion-MFC but not detected in the SPEEK-MFC. Interestingly, the clone closely related to Acetobacterium malicum strain HAAP-1, belonging to the homoacetogens, became dominant in both anolytic and biofilm communities of the SPEEK-MFC. It was suggested that the lower proton conductivity of SPEEK-MEA allowed the bacteria closely related to strain HAAP-1 to be dominant specifically in SPEEK-MFC. These results indicated that Nafion-MFC ranked with SPEEK-MFC and that MEAs had strong selective pressure for electricity-producing bacterial community.

Adaptation of soil microbes during establishment of microbial fuel cell consortium fed with lactate.

We report the development of microbial populations and changes in their electrochemical production during a 2-month study of a two-chamber microbial fuel cell (MFC). The original inoculum was taken from anaerobic enrichment cultures with soil as the inoculum, and lactate as the exogenous electron donor. Power density (PD), coulombic production (CP), and coulombic efficiency (CE) increased rapidly, reaching high values (320 mW m(-3), 65 Q, and 12.5%, respectively) in 12-16 days. Under these conditions, several major microbial taxa dominated the anode population. The medium solution in the cathode chamber decreased with aeration, resulting in a decrease in PD to 55 mW m(-3) at day 20. Refilling the cathode chamber around day 30 resulted in restoration of the PD, CP and CE to values equal to or greater than those previously observed. However, after the change in conditions, a marked change in community structure was observed, and high levels of acetate were seen in the anode chamber of the fuel cell for the first time. At day 35, a series of lactate concentrations were used, beginning with low levels and increasing to the 20 mM level originally used (day 46), the PD decreased but was stable at 150 mW m(-3) and the acetate concentration in the anode stabilized at about 35 mM. Under these conditions, new major population structures, which were closely related to Propionibacterium, Clostridium, and uncultured bacteria, were observed in the anode. These results suggested that the flexibility of community structure was important for sustainable electricity production.