DAAD meeting, Alessandro Carmona
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DAAD meeting, Alessandro Carmona
- 1. Meeting of DAAD-Scholarship holders in Hannover 2009 „Microbial fuel cells: an alternative for the production of clean electricity” Alessandro Carmona Group of Sustainable Chemistry and Energy Research, Institute of Ecological Chemistry and Waste Analysis, Technische Universität Braunschweig http://www.oekochemie.tu-bs.de TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 2. Index • Fossil fuels – Environmental disadvantages – An example for energy alternatives: Microbial fuel cells • Microbial fuel cells – Operating principles – Cells Designs and microorganisms as inocula • Electron transfer mechanisms – Direct electron transfer – Mediated electron transfer • Power production – Characterization – Energy flux – Potential losses • Conclusions Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 3. Global Energy Systems Transition, 1850-2150 100 80 60 40 20 0 1850 1900 1950 2000 2050 2100 2150 Año Porcentaje del mercado total Gases Liquids Oil Animal Oil CH4 CH4 H2 Year Wood Solids Carbon and nuclear Use (%) Increasingly Sustainable Economic Growth Decentralized, less capital intensive technologies Non-Sustainable Economic Growth Centralized, capital intensive technologies Adapted from Dunn, S. (2002), Int. J. Hydrogen Energy, 27 (3): 235-64 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 4. Microbial fuel cells …are a unique subset of fuel cells that take advantage of microbial metabolism to either generate fuels for commercial fuel cells or electricity directly Biffinger and Ringeisen (2008), Recent Pat Biotechnol, 2 (3): 150-155 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 5. Diagram of a microbial fuel cell Reaction process example at the anode: C6H12O6 + 6H2O ® 6CO2 + 24H+ + 24e- e- e- e- e- e- e- Anode Cathode Physical Separator MEDox Soluble organic substrate Microorganism MFC structure H2O Reaction process example at the cathode: 6O2 + 24H+ + 24e- ® 12H2O H+ e- H+ MEDred NADH NAD+ NAD+ Glucose CO2 H+ e-e-e- Air e- O2 e-e- H+ H+ Adapted from Schröder (2008), ChemSusChem, 1: 281-282 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 6. Schematic drawing of the energy flux in a microbial fuel cell Adapted from Schröder (2007), PCCP, 9: 619–2629 Biological energy dissipation Substrate Microorganism (fuel) Electricity Anode Cathode H+ H+ H2O O2 ΔGѲ´ biol ΔGѲ elec EѲ´ fuel EѲ´ link EѲ´ ox (CO2/Glucose: -0.43 V) ΔGѲ total=nF ΔE Ѳ´ (O2/H2O: +0.82 V)
- 7. Electron transfer mecanisms Mediated Direct electron transfer electron transfer (A) membrane bound cytochromes (B) electronically conducting nanowires Simplified, schematic illustration of MET via microbial secondary metabolites Simplified, schematic illustration of MET via microbial primary metabolites Taken from Schröder, 2007, PCCP, 9: 619–2629 Rosenbaum et al., 2006, Angew. Chem. Int. Ed., 455: 6658-6661 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 8. Types of MFCs used in studies A B C E F D H G A. Min et al. (2005). Water Res. 39: 1675-1686. B. Rabaey et al. (2005). Environ. Sci. Technol. 39: 3401-3408. C. Carmona- Martínez et al. (2009). J. New Mater. Electrochem. Syst. In Press . D. Rosenbaum et al. (2005). Environ. Sci. Technol. 39: 6328- 6333. E. He et al. (2005). Environ. Sci. Technol. 39: 5262-5267. F. Min y Logan (2004). Environ. Sci. Technol. 38: 5809-5814. G. Rosenbaum et al. (2005). Appl. Microbiol. Biotechnol. 68: 753-756. H. Liu et al. (2004). Environ. Sci. Technol. 38: 2281-2285.
- 9. Types of microorganisms used in studies G. sulfurreducens C Shewanella putrefaciens A B Oligonucleotides: Arquea (ARC915, green) Bacteria (EUB338, red) D E G. metallireducens strain GS-15 Aeromonas hydrophila KCTC 2358, Geopsychrobacter electrodiphilus F A. Bond y Lovley. (2003). Appl Environ Microbiol. 69: 1548-1555. B. He et al. (2005). Environ. Sci. Technol. 39: 5262-5267. C. Lee et al. (2003). FEMS Microbiol. Lett. . 223: 185-191. D. Pham et al. (2003). FEMS Microbiol. Lett. . 223: 129-134. E. Gregory et al. (2004). Environ Microbiol . 6: 596-604 F. Holmes et al. (2004). Appl Environ Microbiol. 70: 6023-6030.
- 10. 1998 2000 2002 2004 2006 2008 Adapted from Logan and Reagan. (2006). Trends Microbiol. 14: 512-528 10000 1000 100 10 1 0.1 0.01 0.001 Aqueous cathodes Sediment MFCs Air cathodes Air cathodes chemicals Year PAn (mW/m2) Power production in MFCs worldwide Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 11. Potential losses during electron transfer in a MFC 1) Bacterial electron transfer 2) Electrolyte resistance 3) At the anode 4) At the MFC resistance and membrane resistance losses 5) At the cathode 6) Electron acceptor reduction. Taken from Rabaey y Verstraete. (2005). Trends Microbiol. 23: 291-298.
- 12. Conclusions & Outlock • MFCs represent a promising technology for renewable energy production • MFC designs need improvements before a marketable product will be possible • Biocathodes are a welcome advancement in the quest to implement MFCs for practical applications: potential cost savings, waste removal, and operational sustainability • Understanding how the microbial ecology of electricity producing communities develops and changes over time, leads to a new way for renewable and sustainable energy production • Further investigations into the physiology and ecology of microbes that transfer electrons to electrodes are essential to carry out the optimization of MFCs • The research of the different electron transfer mechanisms will lead to better understand the processes of the bioelectrochemical energy conversion, for the further development of this technology • The MFC technology will have to compete with the mature current technologies (i.e. methanogenic anaerobic digestion) that have seen wide commercial applications Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 13. -The End - I kindly thank your attention… Group of Sustainable Chemistry and Energy Research alessandro.carmona@tu-bs.de Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 14. Integration of anaerobic digestion and MFCs for the treatment of wastewaters Taken from Pham et al. (2006), Eng. Life Sci. 6 (3): 285-292. Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 15. Polarization and power curves I. Activation losses II. Ohmic losses III. Concentration losses I = E CCM CCM R ext Rext>>> 0 W CCM CCM CCM P = E I Rext> 0 W Rext>> 0 W Taken from Logan et al. (2006). Environ. Sci. Technol. 17: 5181.5192 Heilman y Logan. (2006). Int. J. Hydrogen Energy. 78, 5: 531-537 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
- 16. Schematic comparison between H2/O2 fuel cells and MFCs Biffinger and Ringeisen (2008), Recent Pat Biotechnol, 2 (3): 150-155 Meeting of DAAD-Scholarship holders in Hannover 2009 TECHNISCHE UNIVERSITÄT CAROLO-WILHELMINA ZU BRAUNSCHWEIG
Editor's Notes
- i. Until the middle of the 19th century, reliance on wood for energy was common in most settled parts of the world. But wood began to lose out to coal, an energy source that was as abundant as wood but more concentrated, and not as bulky or awkward to transport. ii. By 1900 the advantages of an energy system based on fluids, rather than solids, began to emerge. This shift created opportunities for oil, which featured a higher energy density and an ability to flow through pipelines and into tanks. iii. But dominant as oil is, the liquid now faces an up-and-coming challenger - a gas. Natural gas, in addition to being cleaner and lighter and burning more efficiently, can be distributed through a network of pipes that is less conspicuous, more efficient, and more extensive than the one used for oil. iv. But do we really want to use these fuels? Climate change is being driven by the atmospheric release of greenhouse gases like CO2. Oil will not suddenly run out, but it is a finite resource. We must develop energy-saving technologies that can stretch oil reserves while we modify our energy-use patterns and infrastructure to become more sustainable. A sustainable energy portfolio should include a variety of carbon-neutral and renewable energy technologies. Existing technologies based on solar, wind, and biomass energy will all be needed to meet our future energy demands. Microbial fuel cells (MFCs), which convert biochemical to electrical energy, may be part of the picture.
- Microbial fuel cells are a unique subset of fuel cells that take advantage of microbial metabolism to either generate fuels for commercial fuel cells or electricity directly.
- Description 1. A bacterium in the anode compartment transfers electrons obtained from an electron donor (glucose) to the anode electrode. This occurs either through direct contact, nanowires, or mobile electron shuttles (small spheres represent the final membrane associated shuttle). During electron production, protons are also produced in excess. These protons migrate through the cation exchange membrane (CEM) into the cathode chamber. The electrons flow from the anode through an external resistance (or load) to the cathode where they react with the final electron acceptor (oxygen) and protons. Description2. Generally speaking, a MFC is an electrochemical device in which microbially produced reduction equivalents are utilized to deliver electrons to a fuel cell anode. The biocatalyst is located in the anodic fuel cell compartment facilitating the oxidation of the substrate (fuel) as well as the transfer of the liberated electrons to the anode.
- In biotechnological processes (including MFCs) microorganisms are denoted as biocatalysts. Referring to MFCs, the use of this term is, strictly speaking, wrong. The definition of a catalyst implies that the catalyst does not appear in the balance of the catalyzed reaction. Yet, in a MFC this is precisely not the case-the microorganism decisively determines the balance of the reaction. The microorganism may facilitate the conversion of the chemical energy of a substrate into electricity, but it retains a distinct portion of the Gibbs free energy, for its own surviving and reproduction. The energy gain for the microorganism (hence, the loss of electric energy for a MFC) is by all means wanted and necessary.
- Direct electron transfer: It takes place via a physical contact of the bacterial cell membrane or a membrane organelle with the fuel cell anode, with no diffusional redox species being involved in the electron transfer from the cell to the electrode. The direct electron transfer requires that the microorganisms possess membrane bound electron transport protein that transfer electrons from the inside of the bacterial cell to its outside, terminating in an outer membrane (OM) redox protein that allows “the electron transfer” to an external, solid electron acceptor. In the case of these organisms the MFC anode can conveniently resume the role of the solid electron acceptor (DET-A). Recently it has been demonstrated that, e.g., some Geobacter and the Shewanella strains can evolve electronically conducting molecular pili (nanowires) that allow the microorganism to reach and utilize more distant solid electron acceptors. These pili also allow the organisms to use an electrode that is not in direct cell contact as its sole electron acceptor (DET-B). Mediated electron transfer via secondary metabolites. iii. For MFC applications, the secondary metabolites (endogenous redox mediators) are especially of great interest, as their synthesis makes the electron transfer independent of the presence of exogenous redox shuttles. The mediator serves as a reversible terminal electron acceptor, transferring electrons from the bacterial cell either to a solid oxidant (the MFC anode!) or into aerobic layers of the biofilm, where it becomes re-oxidized and is again available for subsequent redox processes. One molecule can thus serve for thousands of redox cycles. Mediated electron transfer via primary metabolites. iv. In contrast to the secondary metabolites the production of reduced primary metabolites is closely associated with the oxidative substrate degradation. Naturally, the total amount of reduction equivalents produced matches the amount of oxidized metabolites. So far, only a few examples of the purposeful utilization of anaerobic respiration for MFC operation (MET1-A) have been reported. In principle, any terminal electron acceptor that has a redox potential sufficiently negative to that of the oxygen electrode, that is reversibly oxidizable, and that is soluble in water in its reduced and oxidized form, can be utilized to establish the anodic electron transfer in a MFC. v. More intensively studied than anaerobic respiration is the use of fermentation for MFC operation. Thus, a large variety of fermentative and photo-heterotrophic processes result in the production of energy-rich reduced metabolites such as hydrogen, ethanol or formate. These compounds can be oxidized directly in the microbial medium, provided electrocatalytic anodes are used to facilitate the oxidation (MET1-B) and measures are taken to prevent a scavenging of the metabolites by other, e.g., biological, processes.
- A: Two chamber MFC containing one electrode each. The separated bottles were connected with a glass tube with a proton exchange membrane. B: Four batch-type MFCs where the chambers are separated by the membrane (without a tube) and held together by bolts. C: Single-chamber, air-cathode system in a simple “tube” arrangement. D: Three electrode arrangement photoheterotrophic (Rhodobacter sphaeroides) type MFC. E: Upflow, tubular type MFC with anode below and cathode above, the membrane is inclinated. F: Flat plate design where a channel is cut in the blocks so that liquid can flow in a serpentine pattern across the electrode. G: Green alga Chlamydomonas reinhardtii MFC. H: Single-chamber system with an inner concentric air cathode surrounded by a chamber containing graphite rods as anode.
- A: Scanning electron microscope (SEM) image of an electrode surface following growth of G. sulfurreducens with acetate as an electron donor (2 mM) under poised potential conditions. Over 75% of viewed fields at this magnification had no exposed electrode; however, this image was chosen to provide an example of electrode surface characteristics and show individual bacterial attachment. B: Fluorescent in situ hybridization (FISH) image of the biomass sampled from the anode electrode on day 85. C: Micrographs of electrodes retrieved from MFCs enriched with acetate. D: Scanning electron micrograph of the anode from the MFC inoculated by cell suspension of Aeromonas hydrophila PA3. The electrode was removed after 5 days of operation with yeast extract as fuel. E: Scanning electron micrograph showing the surfaces of working chamber electrodes inoculated with river sediment, nitrate and enriched with a poised (-500 mV relative to Ag/AgCl) electrode. F: Thin-section electron micrograph of a whole cell of strain A1T Geobacter grown on medium with poorly crystalline Fe(III) oxide (100 mM) provided as the electron acceptor and acetate (10 mM) as the electron donor.
- Power production for MFCs shown over time on the basis of published results. In less than a decade, power production by MFCs has increased by several orders of magnitude. Power production continues to be limited by systems that have the cathode immersed in water [aqueous cathodes (red triangles) and sediment MFCs (green diamonds)]. Substantial power production has been possible by using air-cathode designs in which the cathode is exposed to air on one side and water on the other side (blue squares). In general, wastewaters have produced less power than systems using pure chemicals (glucose, acetate and cysteine in the examples shown; purple circles). Not included in this figure are systems that are based on: hydrogen produced by fermentation because the substrate is incompletely consumed in fermentation-based reactions or they require light; or systems using ferricyanide at the cathode because power production by these systems is not sustainable as a result of the need to regenerate chemically the ferricyanide consumed in the reaction.
- The amount of energy gained out of an electrochemical process can be calculated based on power output and process duration. The power depends both on the voltage V and the current I. The latter factors are linked by the fuel cell resistance. What is measured over the fuel cell will be lower than the attainable voltage. In practice, the maximal open circuit potentials observed are of the order of 750–800 mV. Upon closure of the electrical loop, this voltage decreases significantly, mainly because of the so-called overpotentials, which are potential losses owing to electron transfer resistances and internal resistances. Three kinds of overpotentials can be defined: a) activation overpotentials, b) ohmic losses and c) concentration polarization. For MFCs, the activation overpotential appears to be the major limiting factor. This overpotential is largely dependent on the current density flowing through the anode, the electrochemical properties of the electrode, the presence of mediating compounds and the operational temperature.
- Proposed models for the integration of anaerobic digestion and microbial fuel cells for the treatment of wastewaters. (A) For domestic wastewater, (B) For industrial wastewater. Note: AD: Anaerobic digestion; MFC: Microbial fuel cell; WTP: Wastewater treatment process.
- Polarization curves. They represent a powerful tool for the analysis and characterization of fuel cells. A polarization curve represents the voltage as a function of the current. Polarization curves can be recorded for the anode, the cathode, or for the whole MFC using a potentiostat. Using a periodical decrease (or increase, when starting at short circuit) of the load, the voltage is measured and the current is calculated using Ohms law. Polarization curves can generally be divided in three zones: (i) starting from the OCV at zero current, there is an initial steep decrease of the voltage: in this zone the activation losses are dominant; (ii) the voltage then falls more slowly and the voltage drop is fairly linear with current: in this zone the ohmic losses are dominant; (iii) there is a rapid fall of the voltage at higher currents: in this zone the concentration losses (mass transport effects) are dominant (solid line). In MFCs, linear polarization curves are most often encountered (dashed line). For a linear polarization curve, the value of the internal resistance (Rint) of the MFC is easily obtained from the polarization curve as it is equal to the slope (dashed line). Power Curves. A power curve that describes the power (or power density) as the function of the current (or current density) is calculated from the polarization curve. As no current flows for open circuit conditions, no power is produced. From this point onward, the power increases with current to a maximum power point, MPP. Beyond this point, the power drops due to the increasing ohmic losses and electrode overpotentials to the point where no more power is produced (short circuit conditions).
- A comparison between standard PEM fuel cell technology and MFCs are presented in the slide. The benefits of using MFC technology include the use of unpurified waste or biomass as fuels, operation under ambient conditions, and no requirement of excess heat for activation or operation.