• Título:  MICROBIAL FUEL CELL PERFORMANCE: DESIGN, OPERATION AND BIOLOGICAL FACTORS
• Autor:  Uria Moltó, Naroa
• Universidad:  Universidad Autónoma de Barcelona
• Departamento:  GENETICA Y MICROBIOLOGIA
• Fecha de Lectura:  07/09/2012
• Programa de doctorado:  Microbiologia
• Dirección: 
  • Mas Gordi, Jordi (DIRECTOR)
• Tribunal: 
  • ESTEVE NUÑEZ, ABRAHAM (PRESIDENTE)
  • FERRERA CEADA, ISABEL (SECRETARIO)
  • SABATÈ VIZCARRA, NEUS (VOCAL)
• Descriptores: 
  • MICROBIOLOGIA
  • ELECTROQUIMICA
• Localización:  UNIVERSITAT AUTÒNOMA DE BARCELONA
• 2012uriammicro.pdf
• Resumen:
  A Microbial Fuel Cell (MFC) is a bioelectrochemical system, in which bacteria oxidize organic matter and transfer the electrons through their electron transport chains onto an electrode surface producing electricity. The efficiency of the system depends on the metabolic activity of the microorganisms growing at the anode but also on a large number of factors related to the design and operation of the MFC. The purpose of this work is to contribute to the analysis and control of some of these factors as well as to throw some light on the role of different electron transfer mechanisms in MFC operation. To achieve this goal different experiments using the electrogenic bacterium Shewanella oneidensis MR-1 have been carried out. First of all, this works analyses the role of several design factors in MFC performance. This part of the research focuses on the effect of different abiotic catalysts (Fe-based soluble catalysts and platinum-based surface catalysts) as well as the cathode to anode ratio required for unhindered power output. The results indicate that soluble catalysts such as ferricyanide operating with carbon cathodes allow much higher power values and therefore need smaller cathode/anode ratios than platinum-based cathodes. In the long term, however, MFCs containing soluble iron catalysts show a progressive degradation of fuel cell performance make them unfit for applications requiring extended operations. In recent years, the search for a suitable catalyst at the cathode has led researchers to explore the possible use of biocathodes. In this work we demonstrate the capacity of Shewanella oneidensis MR-1 to catalyse the cathode reaction both under aerobic and anaerobic conditions, being able to sustain the current provided by bacteria present in the anode. Shewanella oneidensis MR-1 biocathodes show the best performance when oxygen is used as the electron acceptor, with results clearly comparable to those obtained with platinum cathodes indicating the efficiency of this bacterium in the catalysis of oxygen reduction. The potential of anode bacteria for current production does not only depend on the levels of microbial activity and on the removal of cathodic limitations but seems to be also affected by factors related to the operation of the system as it has been observed with the anode potential or the external resistance. In addition to these, we have shown the importance of continuous MFC operation as another important factor to take into account for some applications. Periods of circuit interruption produce an alteration of the normal current output in the form of defined current peaks that appear when closing the circuit after a short period of current interruption and that decay slowly back to the original stable values. In depth analysis of this response demonstrates the capacity of Shewanella oneidensis MR-1 to store charge when no electron acceptors are present. Finally, a series of experiments were designed using different anode coatings to help determine the contribution of the different electron transfer mechanisms to current production in MFCs harbouring complex microbial communities. The MFC with a naked anode shows that direct electron transfer mechanisms are responsible for most of the current generated. The microbial community formed agrees with the electron transfer pathways available. So, this MFC presents species able of direct and mediated electron transfer as Shewanella, Aeromonas, Pseudomonas or Propionibacterium. The MFC sustained by shuttle-dependent electron transfer follows in importance being responsible for as much as 40% of current output. This reactor shows a great quantity of different redox species in the anolyte bulk, some of them not related to mediators currently described in the literature. Finally, in the MFC with a nafion-coated anode, the only chemical species able to diffuse to the anode surface is hydrogen. In this case, current production is sustained by the interaction between some organisms, such as Comamonas, Alicycliphilus, Diaphorobacter or the archaea Methanosaeta and the anode. Oxidation of acetate by these microorganisms results in hydrogen production that is therefore oxidised at the anode surface after crossing the nafion barrier. Current production by this mechanism would account for not more than 5% of the total current evolved in an unres