Electrochemical characterization of Geobacter lovleyi identifies limitations of microbial fuel cell performance in constructed wetlands

Power generation in microbial fuel cells implemented in constructed wetlands (CW-MFCs) is low despite the enrichment of anode electricigens most closely related to Geobacter lovleyi. Using the model representative G. lovleyi strain SZ, we show that acetate, but not formate or lactate, can be oxidized efficiently but growth is limited by the high sensitivity of the bacterium to oxygen. Acetate and highly reducing conditions also supported the growth of anode biofilms but only at optimal anode potentials (450 mV vs. standard hydrogen electrode). Still, electrode coverage was poor and current densities, low, consistent with the lack of key c-type cytochromes. The results suggest that the low oxygen tolerance of G. lovleyi and inability to efficiently colonize and form electroactive biofilms on the electrodes while oxidizing the range of electron donors available in constructed wetlands limits MFC performance. The implications of these findings for the optimization of CW-MFCs are discussed. [Int Microbiol 20(2):55-64 (2017)]Keywords: microbial fuel cells; bioelectrochemical systems; constructed wetlands; extracellular electron transfer; electricigen

Electrochemical characterization of Geobacter lovleyi identifies limitations of microbial fuel cell performance in constructed wetlands

Microbial Fuel Cells implemented in Constructed Wetlands (CW-MFCs) show limited performance. Geobacter Lovleyi has been demonstrated to be one of the predominant bacterial species in active CW-MFCs. The aim of this study was to characterize the growth of G.Lovleyi so as to identify if it could be a source for the observed CW-MFCs low performances. To this aim, G. Lovelyi was grown under three different electron donors (acetate, lactate and formate) and two electron acceptors (fumarate and Fe(III) citrate). G. Lovleyi growing and electron transfer characteristics was also studied by inoculating it in double chambered MECs (anodes poised at 31, 450 and 771 mV). Results showed that its growth was supported by acetate, with doubling times of 4.4±0.1 and 8±0.1 hours for fumarate and Fe(III) citrate as electron acceptors, respectively. G. Lovleyi was also demonstrated to be highly intolerant to oxygen, requiring cysteine as a reducing agent. In contrast, formate and lactate did not support cell growth even in the presence of cysteine. Maximum currents achieved were that of 0.08 mA and 0.26 mA for the MECs operated at 450 mV and 771 mV, respectively. However, no current was observed at 31mV. Confocal laser scanning microscopy (CLSM) analysis showed poor electrode coverage, indicating that G. Lovleyi did not attach to the electrode effectively. According to these results, low performances of CW-MFCs could by at least partially explained by the inability of G. lovleyi to oxidize the wide range of metabolites present in CW, to tolerate even trace oxygen concentrations or to efficiently attach to electrodes surface.Peer ReviewedPostprint (published version

Improved limits on nuebar emission from mu+ decay

We investigated mu+ decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for \nueb via the detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays was identified. We extract upper limits of the branching ratio for the LF violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ -> e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which \nueb emission from mu+ decay is allowed with considerable strength. The decay \mupdeb as source for the \nueb signal observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl

The KATRIN Pre-Spectrometer at reduced Filter Energy

The KArlsruhe TRItium Neutrino experiment, KATRIN, will determine the mass of the electron neutrino with a sensitivity of 0.2 eV (90% C.L.) via a measurement of the beta-spectrum of gaseous tritium near its endpoint of E_0 =18.57 keV. An ultra-low background of about b = 10 mHz is among the requirements to reach this sensitivity. In the KATRIN main beam-line two spectrometers of MAC-E filter type are used in a tandem configuration. This setup, however, produces a Penning trap which could lead to increased background. We have performed test measurements showing that the filter energy of the pre-spectrometer can be reduced by several keV in order to diminish this trap. These measurements were analyzed with the help of a complex computer simulation, modeling multiple electron reflections both from the detector and the photoelectric electron source used in our test setup.Comment: 22 pages, 12 figure

Characterization measurements of the TRISTAN multi-pixel silicon drift detector

Sterile neutrinos are a minimal extension of the standard model of particle physics. A laboratory-based approach to search for this particle is via tritium β-decay, where a sterile neutrino would cause a kink-like spectral distortion. The Karlsruhe Tritium Neutrino (KATRIN) experiment extended by a multi-pixel Silicon Drift Detector system has the potential to reach an unprecedented sensitivity to the keV-scale sterile neutrino in a lab-based experiment. The new detector system combines good spectroscopic performance with a high rate capability. In this work, we report about the characterization of charge-sharing between pixels and the commissioning of a 47-pixel prototype detector in a MAC-E filter

Characterization measurements of the TRISTAN multi-pixel silicon drift detector

Sterile neutrinos are a minimal extension of the Standard Model of Particle Physics. A laboratory-based approach to search for this particle is via tritium beta-decay, where a sterile neutrino would cause a kink-like spectral distortion. The Karlsruhe Tritium Neutrino (KATRIN) experiment extended by a multi-pixel Silicon Drift Detector system has the potential to reach an unprecedented sensitivity to the keV-scale sterile neutrino in a lab-based experiment. The new detector system combines good spectroscopic performance with a high rate capability. In this work, we report about the characterization of charge-sharing between pixels and the commissioning of a 47-pixel prototype detector in a MAC-E filte