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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]