Electrochemical activity of Geobacter sulfurreducens biofilms on stainless steel anodes

Stainless steel was studied as anode for the biocatalysis of acetate oxidation by biofilms of Geobacter sulfurreducens. Electrodeswere individually polarized at different potential in the range−0.20V to +0.20V vs. Ag/AgCl either in the same reactor or in different reactors containing acetate as electron donor and no electron acceptor except the working electrode. At +0.20V vs. Ag/AgCl, the current increased after a 2-day lag period up to maximum current densities around 0.7Am−2 and 2.4Am−2 with 5mMand 10mM acetate, respectively. No current was obtained during chronoamperometry (CA) at potential values lower than 0.00V vs. Ag/AgCl, while the cyclic voltammetries (CV) that were performed periodically always detected a fast electron transfer, with the oxidation starting around −0.25V vs. Ag/AgCl. Epifluorescent microscopy showed that the current recorded by chronoamperometrywas linked to the biofilm growth on the electrode surface, while CVswere more likely linked to the cells initially adsorbed from the inoculum. A model was proposed to explain the electrochemical behaviour of the biofilm, which appeared to be controlled by the pioneering adherent cells playing the role of “electrochemical gate” between the biofilm and the electrode surface

CHARGE DENSITY WAVE TRANSPORT IN THE BLUE BRONZES K_<0.30>MoO_3 AND Rb_<0.30>MoO_3(EXPERIMENTS ON BLUE BORNZES, International Symposium on NONLINEAR TRANSPORT AND RELATED PHENOMENA IN INORGANIC QUASI ONE DIMENSIONAL CONDUCTORS)

この論文は国立情報学研究所の電子図書館事業により電子化されました。We report data on non linear conductivity and both slow and fast voltage oscillations in the blue bronzes K_MoO_3 and RbK_MoO_3. These properties are attributed to the depinning of the CDW. The data obtained on Rb_MoO_3 are very similar to those obtained previously on K_MoO_3. We have studied in details the slow phenomena, time dependent effects voltage pulses or coherent oscillations both in "pure" and doped K_MoO_3. While pulses are found in the "pure" samples, the doped ones rather show oscillations, more or less coherent depending on the cooling process with or without a dc current. We propose that the slow phenomena are related to the CDW domain boundaries,discommensurations or dislocations in the CDW lattice. We suggest that possible diffusion of defects, possibly impurities, coupled either with the CDW modulation or with the domain boundaries, may account for the time dependent and memory effects

Identification of geometrical and elastostatic parameters of heavy industrial robots

The paper focuses on the stiffness modeling of heavy industrial robots with gravity compensators. The main attention is paid to the identification of geometrical and elastostatic parameters and calibration accuracy. To reduce impact of the measurement errors, the set of manipulator configurations for calibration experiments is optimized with respect to the proposed performance measure related to the end-effector position accuracy. Experimental results are presented that illustrate the advantages of the developed technique.Comment: arXiv admin note: substantial text overlap with arXiv:1311.667

Modelling of the gravity compensators in robotic manufacturing cells

The paper deals with the modeling and identification of the gravity compensators used in heavy industrial robots. The main attention is paid to the geometrical parameters identification and calibration accuracy. To reduce impact of the measurement errors, the design of calibration experiments is used. The advantages of the developed technique are illustrated by experimental result

Application of electro-active biofilms

The concept of an electro-active biofilm (EAB) has recently emerged from a few studies that discovered that certain bacteria which form biofilms on conductive materials can achieve a direct electrochemical connection with the electrode surface using it as electron exchanger, without the aid of mediators. This electro-catalytic property of biofilms has been clearly related to the presence of some specific strains that are able to exchange electrons with solid substrata (eg Geobacter sulfurreducens and Rhodoferax ferrireducens). EABs can be obtained principally from natural sites such as soils or seawater and freshwater sediments or from samples collected from a wide range of different microbially rich environments (sewage sludge, activated sludge, or industrial and domestic effluents). The capability of some microorganisms to connect their metabolisms directly in an external electrical power supply is very exciting and extensive research is in progress on exploring the possibilities of EABs applications. Indeed, the best known application is probably the microbial fuel cell technology that is capable of turning biomass into electrical energy. Nevertheless, EABs coated onto electrodes have recently become popular in other fields like bioremediation, biosynthesis processes, biosensor design, and biohydrogen production

Marine microbial fuel cell : use of stainless steel electrodes as anode and cathode materials

Numerous biocorrosion studies have stated that biofilms formed in aerobic seawater induce an efficient catalysis of the oxygen reduction on stainless steels. This property was implemented here for the first time in a marine microbial fuel cell (MFC). A prototype was designed with a stainless steel anode embedded in marine sediments coupled to a stainless steel cathode in the overlying seawater. Recording current/potential curves during the progress of the experiment confirmed that the cathode progressively acquired effective catalytic properties. The maximal power density produced of 4mWm−2 was lower than those reported previously with marine MFC using graphite electrodes. Decoupling anode and cathode showed that the cathode suffered practical problems related to implementation in the sea, which may found easy technical solutions. A laboratory fuel cell based on the same principle demonstrated that the biofilm-covered stainless steel cathode was able to supply current density up to 140mAm−2 at +0.05V versus Ag/AgCl. The power density of 23mWm−2 was in this case limited by the anode. These first tests presented the biofilm-covered stainless steel cathodes as very promising candidates to be implemented in marine MFC. The suitability of stainless steel as anode has to be further investigated

Checking graphite and stainless anodes with an experimental model of marine microbial fuel cell

A procedure was proposed to mimic marine microbial fuel cell (MFC) in liquid phase. A graphite anode and a stainless steel cathode which have been proven, separately, to be efficient in MFC were investigated. A closed anodic compartment was inoculated with sediments, filled with deoxygenated seawater and fed with milk to recover the sediment’s sulphide concentration. A stainless steel cathode, immersed in aerated seawater, used the marine biofilm formed on its surface to catalyze oxygen reduction. The cell implemented with a 0.02 m2-graphite anode supplied around 0.10 W/m2 for 45 days. A power of 0.02 W/m2 was obtained after the anode replacement by a 0.06 m2-stainless steel electrode. The cell lost its capacity to make a motor turn after one day of operation, but recovered its full efficiency after a few days in open circuit. The evolution of the kinetic properties of stainless steel was identified as responsible for the power limitation

Electrochemical oxidation of acetate by Geobacter sulfurreducens : Influence of anode materials

The recent discovery of micro-organisms that could transfer directly electrons to insoluble electrode [1] had encouraged the researches on microbial fuel cells. The interfaces anode/micro-organism are explored to enhance the bacterial electron transfer and increase the power densities produced: some modified anodes have been designed, binding for example electron mediators (Mn4+, neutral red …) to woven graphite [2]. Moreover the porosity of different forms of carbon has been found to influence current productions [3]. The purpose of this work was to compare the efficiency of graphite, DSA® and stainless steel as anode materials for growing Geobacter sulfurreducens under imposed potential conditions. Current densities obtained were seven times higher than values presented in literature [4] and depended on anode material. Analyses of the electrode surface with techniques like optical interferometry, SEM or confocal microscopy revealed significant differences in roughness and bacterial coverage, which may explain the variety of current densities obtained

On the coupling of wave and three-dimensional circulation models : Choice of theoretical framework, practical implementation and adiabatic tests

Many theoretical approaches and implementations have been proposed for the coupling of the three-dimensional ocean circulation with waves. The theoretical models are reviewed and it is shown that the formulation in terms of the quasi-Eulerian velocity circumvents the essential difficulty of alternative formulations for the Lagrangian mean velocity. Namely, models based on this Lagrangian velocity require an estimation of wave-induced motions to first order in the horizontal gradients of the wave field in order to estimate the vertical flux of wave pseudo-momentum. So far, only three-dimensional wave models have been able to provide these estimates, and all published theories based on the simpler Airy theory are not consistent at the leading order, because they ignore or incorrectly estimate the vertical momentum flux. With an adiabatic example on a sloping bottom it is shown that this inconsistency produces very large spurious velocities. These errors are independent of the slope for the inviscid case, and are still significant when a realistic vertical mixing is applied. A quick diagnostic of the potential accuracy of a theoretical model is the vertical profile of the wave-induced forcing terms: if it is not uniform over depth in adiabatic conditions then it will produce spurious artificial flow patterns in conditions with shoaling waves. Although conceptually more challenging, the quasi-Eulerian velocity theories only introduce minor modifications of the solution procedure for the standard primitive equations: a modification of the surface boundary condition for the mass conservation, the addition of the Stokes drift in the tracer advection equations, and sources of momentum and turbulent kinetic energy with associated surface and bottom fluxes. All the necessary modifications of primitive equation models are given in detail. This implementation is illustrated with the MARS3D model, which passes the test of the adiabatic shoaling waves

Catalyse électro-microbienne dans les piles à combustible

Les piles à combustible microbiennes (PACM) sont des systèmes qui assurent la conversion directe de matières organiques en énergie électrique en utilisant des biofilms bactériens comme catalyseur des réactions électrochimiques. Cette étude vise à améliorer la compréhension des mécanismes de transfert électronique entre les bactéries adhérées et les électrodes, ainsi qu'à optimiser la production électrique des PACMs en explorant et caractérisant différents matériaux d'électrodes. Les expériences effectuées en réacteur d'électrolyse sur la souche Geobacter sulfurreducens portent sur la catalyse électro-microbienne de l'oxydation de l'acétate, d'une part et de la réduction du fumarate d'autre part. Du côté anodique, des différences de densités de courant apparaissent sur graphite, DSA® et acier inoxydable (8A/m², 5A/m² et 0,7A/m² respectivement). Ces écarts sont attribués aux différences de rugosité des matériaux plutôt qu'à leur nature. Une étude par spectroscopie d'impédance montre que le biofilm électroactif qui se développe sur l'acier inoxydable ne semble pas modifier les couches d'oxydes du matériau, seul le potentiel imposé reste déterminant. Du côté cathodique, l'acier inoxydable a permis d'obtenir des densités de courant plus de vingt fois supérieures à celles obtenues avec des électrodes de graphite. L'étude de l'adhésion de G.sulfurreducens sur les différents types de matériaux en cellule à écoulement cisaillé, suggère que les biofilms résistent bien aux contraintes hydrodynamiques et ne se détachent pas en-dessous d'une valeur seuil du taux de cisaillement. L'installation de deux prototypes de PACM, l'un en station marine et l'autre directement dans le port de Gênes (Italie) confirme certains résultats obtenus en laboratoire et s'avère prometteur pour l'extrapolation des PACMs à l'échelle pilote. ABSTACT : Microbial fuel cells (MFC) are devices that ensure the direct conversion of organic matter into electricity using bacterial biofilms as the catalysts of the electrochemical reactions. This study aims at improving the comprehension of the mechanisms involved in electron transfer pathways between the adhered bacteria and the electrodes. This optimization of the MFC power output could be done, for example, in exploring and characterizing various electrode materials. The electrolysis experiments carried out on Geobacter sulfurreducens deal with the microbial catalysis of the acetate oxidation, on the one hand, and the catalysis of the fumarate reduction on the other hand. On the anodic side, differences in current densities appeared on graphite, DSA® and stainless steel (8A/m², 5A/m² and 0.7A/m² respectively). These variations were explained more by materials roughness differences rather than their nature. Impedance spectroscopy study shows that the electroactive biofilm developed on stainless steel does not seem to modify the evolution of the stainless steel oxide layer, only the imposed potential remains determining. On the cathodic side, stainless steel sustained current densities more than twenty times higher than those obtained with graphite electrodes. The adhesion study of G.sulfurreducens on various materials in a flow cell, suggests that the biofilms resist to the hydrodynamic constraints and are not detached under a shear stress threshold value. The installation of two MFC prototypes, one in a sea station and the other directly in Genoa harbour (Italy) confirms some results obtained in laboratory and were promising for a MFC scale-u