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BEEMS Module B8 Microbial Fuel Cells BEEMS Ann D. Christy Department of Food, Agricultural, and Biological Engineering The Ohio State University Contact: Ann D. Christy, [email protected] Sponsored by: USDA Higher Education Challenger Program 2009-38411-19761 Outline Introduction to Microbial Fuel Cells (MFCs) Comparison with other technologies Current applications Technical challenges Research frontiers Introduction to Microbial Fuel Cells Bio-electro-chemical devices which convert chemical energy directly into electrical energy Cellulose Sugars Hydrolysis Short chain fatty acids Alcohols Hydrogen Carbon dioxide Fermentation Electricity Carbon dioxide Electricigenesis Electricigenic microbes 3 Components of an MFC • Anaerobic anode chamber (contains microbes and feedstock) • Aerobic cathode chamber • Proton Exchange Membrane (PEM) which separates the two chambers and allows only protons (H+ ions) to pass Lovley, D.R. 2008. The microbe electric: conversion of organic matter to electricity. Current Opinion in Biotechnology 19:564-571. Anaerobic respiration (also known as Cellular respiration) A micro-organism’s method to gain useful energy Set of metabolic reactions to convert chemical energy from nutrients to adenosine triphosphate (ATP) and then dispose of wastes Three steps of respiration: 1. 2. 3. Glycolysis Kreb’s / Citric Acid Cycle Electron transport chain (SEM from Bond and Lovley. 2003. Electricity production by Geobacter sulfureducens attached to electrodes. Appl Environ Microbiol 69:1548– 1555. 1. Glycolysis Glucose (C6H12O6) is broken into two molecules of pyruvic acid (CH3‐CO‐COOH or pyruvate), and two adenosine triphosphate (ATP) molecules ATP is used by the cell to store and release small quantities of energy, switching between ATP and ADP (adenosine diphosphate) as one of the phosphate-to-phosphate bonds is alternately broken (ATP -> ADP releasing energy) and rebuilt (ADP -> ATP storing energy) 2. Kreb’s / Citric acid cycle Pyruvic acid (from Step 1 Glycolysis) is broken down into CO2, releasing a series of metabolites In the process, metabolic energy is captured as ATP, NADH, and FADH2 http://web.virginia.edu/Heidi/chapter 20/chp20.htm 3. Electron transport chain Electrons from the electron donor (feedstock, substrate, for example: glucose) are transported down the electron transport chain to the terminal electron acceptor Protons (H+ ions) are translocated across the microbial cell membrane from inside the cell to outside (from Alberts, et al., 2002) Anaerobic respiration in MFCs CO2 H2O O2 Substrate Rabaey, K., Verstraete, W. 2005. Microbial fuel cells: Novel biotechnology for energy generation. Trends. Biotechnol. 23:291298. • For the electron transport chain to function, a final electron acceptor must take each electron away from the system after it is used • Instead of a normal electron acceptor (e.g., O2, SO4, NO3, S), MFC microorganisms use a solid electrode Extracellular transport of electrons Unique ability of those microorganisms capable of electricigenesis to transfer these electrons outside of their cell wall, coupling anaerobic respiration with use of an external electron acceptor In contrast, fermentation utilizes the internally generated electron acceptor, pyruvate Mechanisms for electron movement a) Direct transfer via cytochromes on outer membrane b) Conductive nanowires (pili) in biofilm a) External or secreted mediators Rinaldi, A., B. Mecheri., V. Garavaglia, S. Licoccia, P. DiNardo, and E. Traversa. 2008. Engineering materials and biology to boost performance of microbial fuel cells: a critical review. Energy & Environmental Science 1:417-429. Choice of MFC microorganisms Advantage: Pure cultures: Mono-cultures (e.g., Geobacter sulfurreducens1) Co-cultures (e.g., Clostridium cellulolyticum + Geobacter sulfurreducens2) Understanding of underlying mechanisms Constraints: Biological contamination Incapable of converting all the end products to electricity Advantage: Microbial consortia 1Bond Digestive tract of ruminants3 Soil4 and Sediment5 Waste water6 and Lovley 2003, 2Ren et al. 2007, 3Rismani-Yazdi et al. 2007, 4Niessen et al. 2006, 4Ishii et al. 2008, Rezai et al 2007, 5Bond et al. 2002, 6Liu and Logan 2004 More robust and efficient than pure cultures for catalyzing of integrated High cellulolytic activities processes Endoglucanases Collective catalytic activities Exoglucanases Glucosidases Function over a wide range of conditions Anaerobic respirators Composition of MFC bacterial communities Planktonic Anode-biofilm 1% 3% 5% 7% 12.6% Comamonas spp. 75.9% 5.7% 5.8% Clostridium spp. Geovibrio spp. 25% 59% Iron reducers Nitrate reducers Betaproteobacteria A consortium of hydrolytic, fermentative and respiratory anaerobes Firmicutes Spirochaetes Firmicutes couple the Unidentified hydrolysis of cellulose with the reduction of the anode bacteria Bacteroidetes Deferribacteres DGGE profiles Gammaproteobacteria Proteobacteria Unidentified bacteria DGGE profiles Rismani-Yazdi et al., 2007. Biotechnol. Bioeng. 97:1398-1407. 14 Electron transport chain to electricity Electrons flow from the anode through a wire to the cathode where electron acceptors are reduced. Protons flow across a proton exchange membrane (PEM) to complete the circuit. ANODE CATHODE PEM Membrane Cathode Anode Not to Scale 6CO2 + 24e- + 24H+ ee- 2CO2 + 8e- + 8H+ Acetate ee- n=1 e- Glucose e- β-Glucan (n ≤7) H+ n≥2 Propionate Cellodextrin Bacteria Cell Wall O2 H+ Anode β-Glucan (n≤7) Cathode Cellulose 3CO2 + 28e- + 28H+ H2O Anode compartment Glucan (n-1) noβ-single microbial Proton Exchange Membrane To date, species has been reported to catalyze the entire process Butyrate Bacteria Cell 4CO2 + 18e- + 18H+ Cathode compartment Example Output of an MFC Power Voltage Rismani-Yazdi, H., Christy, A. D., Dehority, B.A., Morrison, M., Yu, Z. and Tuovinen, O. H. 2007. Electricity generation from cellulose by rumen microorganisms in microbial fuel cells. Biotechnol. Bioeng. 97:1398-1407. Comparison with other technologies Gasification Fuel gas combustion Combustion Pyrolysis Pyrolytic oil Hydrolysis Hydrolysis Extraction Sugar fermentation Ethanol Butanol Heating Biogas H2, CH4 co2 Crop residues (corn stover, straw) Animal manures Food / feed processing residues Wood processing residues Municipal solid waste Microbial Fuel Cell Electrical devices Anaerobic fermentation Microbial Fuel Cell Application Transport Anaerobic respiration Biofuels and Bioenergy Heat Conversion processes Electricity Cellulosic biomass Liquid biofuels 6CO2 + 6H2O C6H12O6 + 6O2 Photosynthesis Comparison to other Fuel Cells • Temperature: moderate (20-40°C) • Fuel: wide variety of organics • Catalyst: microbial biocatalyst, not precious metals • Electrode materials: biocompatible 19 Current applications •Mass: 16 kg •Power: 36 mW (equivalent to 26 D-cell batteries) Other potential applications of MFCs Food processing plants and breweries Logan, B. E. 2010. Scaling up Microbial Fuel Cells and Other Bioelectrochemical Systems. Applied Microbiology and Biotechnology 85(6):1665-671. Wastewater treatment facilities Liu, H., R. Ramnarayanan, and B. E. Logan. 2004. Production of Electricity during Wastewater Treatment Using a Single Chamber Microbial Fuel Cell. Environmental Science & Technology 38(7): 2281-285. Implanted biomedical devices Siu, C.-P.-B., and Mu Chiao. 2008. A Microfabricated PDMS Microbial Fuel Cell. Journal of Microelectromechanical Systems 17(6): 1329-341. 21 Future Applications LED lighting in remote regions Battery recharging station Implantable biomedical devices (e.g., pacemakers, insulin pumps) If the power can be significantly increased, the list becomes much longer… Technical challenges Comparatively Low Power Densities Rinaldi, A., B. Mecheri., V. Garavaglia, S. Licoccia, P. DiNardo, and E. Traversa. 2008. Engineering materials and biology to boost performance of microbial fuel cells: a critical review. Energy & Environmental Science 1:417-429. 23 Factors affecting MFC performance Engineering Biology • Microorganisms Geometry (e.g., spacing between electrodes) • Feedstocks • Environmental conditions Circuit resistances for microbes (pH, Eh, (internal and external) temperature, metabolic by Batch vs. Continuous products) Proton exchange membrane materials Electrode materials (anode and cathode) 24 Research Frontiers 1. 2. 3. 4. 25 Reactor design Feedstock selection and preparation External resistance Electrode surface area Challenge: Selecting for robust microbial population • Performance of MFCs depends on diversity and activity of microorganisms • Current MFC technology exploits natural microbial selection First step in overcoming this challenge: Identify and characterize operational conditions and engineering design factors that can promote formation of the desired communities Effect of external resistance on bacterial diversity, metabolism and performance of MFCs CO2 Substrate H2O O2 External resistance (R) controls the flow of electrons from the anode to the cathode, affecting voltage (V) and current (I) outputs of MFCs according to Ohm’s Law: V = IR And the power output: W = I2R (Figure from Rabaey & Verstraete, 2005) Rismani-Yazdi, H., A.D. Christy, S.M. Carver, Z. Yu, B.A. Dehority, and O.H. Tuovinen. 2011. Effect of external resistance on bacterial diversity and metabolism in microbial fuel cells. Bioresource Technology 102(1): 278-283. MFCs construction and operation Description Compartments Transparent polycarbonate plastic Dimensions: 25 × 60 62 mm Total volume: 97 ml Working volume: 75 ml Electrodes Polished graphite plates Surface area: 40 cm2 Electrode spacing: 1.6 cm Proton exchange membrane Ultrex CMI-7000 Surface area: 37 cm2 External resistance 249, 480 480 and 1000 External resistances: 20, 20, 249, andΩ1000 Ω Anode catalysts Rumen microorganisms Inoculum size: 10% (V/V) Cathode mediator Potassium hexacyanoferrate Substrate Cellulose Feeding schedule: 1-7 d (5 g/l), 8-90 d (1 g/l every other day) Incubator temperature 39±1ºC Shaker agitation rate 100 rpm -2 -2) ) m density (mW m(mW density PowerPower Power output as a function of external resistance 70 60 External resistance (Ω) Maximum power density (mW m-2) 20 20 66 10 249 57 0 480 53 1000 47 50 40 30 0 100 200 300 400 500 600 700 -2 Current density (mA m ) 20 _ 249 _ 480 _ 1000 _ External resistance can be useful as a tool to control microbial communities and enhance performance of MFCs Rismani-Yazdi, H., A.D. Christy, S.M. Carver, Z. Yu, B.A. Dehority, and O.H. Tuovinen. 2011. Effect of external resistance on bacterial diversity and metabolism in microbial fuel cells. Bioresource Technology 102(1): 278-283. 4. Effects of increasing electrode surface areas in MFCs Higher surface area on the anode provides more sites for electron acceptance and bacterial attachment Higher surface area on the cathode provides more oxygen reduction sites 30 This study: Increasing surface area of MFC cathodes by using… Different base materials: Graphite bar Stainless steel mesh Different adhesives: • Silver epoxy • Conductive graphite paint Different nanostructure surface coatings: 1. 2. 3. Carbon nanotubes Activated carbon granules Graphite powder 31 Cathode electrode material test: Graphite Bar Reference silver epoxy on graphite bar cathode Graphite powder coated Carbon nanotube powder coated 32 Voltage output for MFCs with silver epoxy coated graphite bar cathodes 33 Polarization curves for graphite bar cathodes Best performance: Graphite powder coated 34 Cathode electrode material test: Stainless steel mesh Reference conductive paint on stainless steel mesh cathode Activated carbon coated ↵ Graphite powder coated Carbon nanotube coated 35 Polarization curves for stainless steel mesh cathodes Best performance: conductive paint adhesive, no additive 36 References Alberts, B., D. Bray, J.Lewis, M.Raff, K.Roberts, and J.D. Watson. 2002. Chapter 4: Energy Conversion. In Molecular biology of the cell. 4th ed. Garland Science. http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mboc4&part=A2489 Bond DR, Holmes DE, Tender LM, Lovley DR. 2002. Electrode-reducing microorganisms that harvest energy from marine sediments. Science 295:483–485. Bond, D.R., and D.R. Lovley. 2003. Electricity production by Geobacter sulfureducens attached to electrodes. Appl Environ Microbiol 69:1548– 1555. Lovley, D.R. 2008. The microbe electric: conversion of organic matter to electricity. Current Opinion in Biotechnology 19:564-571. Perlack et al. 2005. Biomass as feedstock for a bioenergy and bioproducts industry: The technical feasibility of a billion-ton annual supply. USDOE-USDA. http://www.puc.state.oh.us/emplibrary/files/media/biomass/BiomassFeedstock.pdf Rabaey, K., Verstraete, W. 2005. Microbial fuel cells: Novel biotechnology for energy generation. Trends. Biotechnol. 23:291-298. Rinaldi, A., B. Mecheri., V. Garavaglia, S. Licoccia, P. DiNardo, and E. Traversa. 2008. Engineering materials and biology to boost performance of microbial fuel cells: a critical review. Energy & Environmental Science 1:417-429. Rismani-Yazdi, H., Christy, A. D., Dehority, B.A., Morrison, M., Yu, Z. and Tuovinen, O. H. 2007. Electricity generation from cellulose by rumen microorganisms in microbial fuel cells. Biotechnol. Bioeng. 97:1398-1407. Rismani-Yazdi, H., A.D. Christy, S.M. Carver, Z. Yu, B.A. Dehority, and O.H. Tuovinen. 2011. Effect of external resistance on bacterial diversity and metabolism in microbial fuel cells. Bioresource Technology 102(1): 278-283. More References Logan, B. 2008. Microbial Fuel Cells. Wiley-Interscience. 216 pages. Rismani-Yazdi, Hamid, Sarah M. Carver, Ann D. Christy, Olli H. Tuovinen. 2008. Cathodic Limitations in Microbial Fuel Cells: An Overview. Journal of Power Sources 180(2): 683-694. Skrinak, N. 2007. Ohio State University’s Microbial Fuel Cell Learning Center. http://digitalunion.osu.edu/r2/summer07/nskrinak/index.htm Tender, L.M., S.A. Gray, E. Groveman, D.A. Lowry, P. Kauffman, J. Melhado, R.C. Tyce, D. Flynn, R. Petrecca, and J. Dobarro. 2008. The first demonstration of a microbial fuel cell as a viable power supply: Powering a meteorological buoy. Journal of Power Sources 179: 571-575. For more information, contact: Ann D. Christy, Ph.D., P.E. Associate Professor Dept. of Food, Agricultural, and Biological Engineering 590 Woody Hayes Drive, 224 Ag Eng Bldg. The Ohio State University Columbus, OH 43210 614-292-3171 [email protected]