Microbial Fuel Cells for autonomous systems : kinetics and technological advances in wastewater treatment and sensor applications
Year: 2012
Type: dissertation
Abstract: Microbial Fuel Cell (MFC) technology is a novel approach for the production of bioelectricity. In MFC, electroactive bacteria oxidize organic matter and have the particularity to transfer the electrons, directly to external electron acceptors producing electricity. Geobacter species are one of the most effective microorganisms known to use electrodes as the sole electron acceptor. In that regard, the present work was focused on the study of the parameters which influence the bacterial electron transfer process to electrodes and on the advancement of wastewater valorization and monitoring technologies based on the MFC concept. The electrochemical behavior of Geobacter sulfurreducens in different stages of the biofilm formation in MFC anodes was assessed by cyclic voltammetry in a three-electrode glass cells with two compartments separated by an ion exchange membrane at room temperature and 35 ºC. Cyclic voltammograms showed that the presence of G. sulfurreducens biofilm results in an increase of current intensities between - 0.5 V and 0.89 V vs. SCE with three well defined oxidation peaks at 0.16 V, 0.6 V and 0.8 V vs. SCE respectively. In mature biofilm the current intensity were higher. The current intensities for both cases were dependent on operating temperature (≈ 22 °C and 35ºC). In every stage of the biofilm formation, the oxidation reaction rate, for the peaks presenting higher current intensities, was limited by the diffusion step with one electron at a time transferred. Besides, the influence of the growth temperature in the induction of pili production and consequence on the expression of the outer membrane proteins of G. sulfurreducens and its effect on the electrochemical behavior as evaluated. Proteins from G. sulfurreducens, cultured at 25 ºC and 37 ºC, were analysed by two-dimensional gel electrophoresis. The results obtained at both temperatures showed that 13 proteins were differentially expressed. The identified proteins were related to membrane permeability, structural integrity, protein’s synthesis and energy generation. From the identified proteins, only the LamB porin family was overexpressed at 37 ºC. Cyclic voltammetry was used to compare the electrochemical behaviour of G. sulfurreducens grown at both temperatures. The results showed a dependency of the electrochemical behaviour of the bacteria, on its growth temperature. Three well-defined oxidation peaks were observed at 0 V, 0.69 V and 0.82 V vs. SCE in voltammograms of bacteria grown at 25 ºC while only two peaks were observed at 37 ºC at 0.08 V and 0.74 V vs. SCE. The oxidation processes characteristic of G. sulfurreducens grown at 25 ºC presented a mixed kinetic control and showed an irreversible behaviour in most sweep rates. At 37 ºC, two distinct irreversible processes were observed, one controlled by diffusion and another by adsorption. A filter-press MFC was adapted for testing electricity production and wastewater treatment. The cell, with 64 cm2 of electrode area (carbon Toray) and 1 cm3 of electrolyte volume, was operated with domestic wastewater in a batch mode (load 622 ± 10 mgL-1 COD) with recirculation in the anodic chamber. In the cathode compartment phosphate buffer with hexacyanoferrate was used. The results showed that the maximum current density increased to 823 Wm-3, resulting in a carbon removal of 84 %. Interruptions in the supply of fresh wastewater slightly decreased power density, while the increase/decrease of the recirculation flow rate did not influence power generation. Finally, a sensor based on the MFC principle was tested for online and in-situ monitoring of Biodegradable Oxygen demand (BOD), a well-known parameter in environmental monitoring in natural waters and wastewater treatment processes. A stable current density of 282 ± 23 mAm-2 was obtained with a wastewater containing a BOD5 of 317 ± 15 mgL-1 O2 at 22 ± 2 °C, 1.53 ± 0.04 mScm-1 and pH 6.9 ± 0.1. The current density showed a linear relationship with BOD5 concentration ranging from 17 ± 0.5 mgL-1 O2 to 78 ± 7.6 mgL-1 O2. The current generation from the BOD biosensor was dependent on the measurement conditions such as temperature, conductivity, and pH. These results provide precise knowledge for the development of a biosensor for real-time in situ monitoring of environmental quality.
Author: L. Peixoto
Language: English
Subfield: Environmental Engineering
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W91145138