Abstract
Microbial Fuel Cells (MFCs) are very interesting in the field of renewable energy because bacteria in wastewater can produce
enough electricity to power small devices. Although the power generation by MFCs has improved by over 100% in the last decade, the
practice is not cost efficient and can rarely power practical devices.
Through this study, a one gallon fuel cell was designed while three
50 mL MFCs were tested in various conditions. If advancements
continue to be made in this field, these fuel cells could possibly help
provide power for devices in remote locations.
Introduction
Why Microbial Fuel Cells?
• Microbial Fuel Cells (MFCs) are devices that harness electricity
from chemical reactions that occur when bacteria decomposes
substrates
• Systems that can directly harvest energy from the environment
can be useful in remote locations like villages or deep in the
ocean
• These renewable, green energy devices have no emissions and
use fuel that is otherwise considered waste
• Improvement has been vast over the last decade
Improving MFC Generation
• Goal is to increase power density and decrease creation costs
• Various materials for anode determine power output - most
current designs use silver or platinum but this one uses carbon
nanotubes to help cost efficiency
• In MFC design, a maximum surface area against the anode material is desirable because it offers a higher
power density
• An external circuit is
necessary to amplify
power up to usable levels
• Various types of wastewater affect the amount
Figure 1: Picture of 50mL MFCs used for
of power produced
various forms of testing
Electrochemically Active
Microbes as
Energy Harvesters
Biology of MFC
[4]
Design
• The goal was to keep MFC simCarbon
Anode
Insert
ple and user-friendly
Nanotube
Cathode
• Air cathode was preferred over
a two chamber system (most
common) because of work constraints
• Maximized surface area by dimensioning a small width which
Bacteria
Chamber
aided in creating a continuous
flow chamber
• Materials included transparent
Figure 4 (above): Exploded AutoCad disacrylic, carbon cloth, and titanium
play of One Gallon MFC with labels
mesh
• Easy access to the electrode because of the removable top plate
• Used multiple 50mL MFCs to test
various conditions (shown in figure 1)
• Wastewater and activated sludge
from a local treatment plant were
compared as the inoculum for the
MFC. During a two week period, the
sludge proved to produce more power
• Analyzed data using Matlab Codes
and Microsoft Excel (flow chart below)
Figure 10 : Carter Creek Wastewater Treatment
Plant with zoomed in wastewater bacteria image [1][2]
Machining
• Parts were dimensioned with a
high tolerance
• Machinery used included band
saws, laser cutters, a milling machine, and a CNC machine
Figure 11 - flow diagram representing process used to analyze
MFC Data and create polarization
curves (shown in next section)
Testing Results
Figure 5 (above: AutoCad Display of One Gallon MFC
50 mL MFC
Figure 12 (right) - This graph shows the inconsistancy of the output voltage from the 50 mL
MFC. This is why Maximum Power Point Control is Necessary on the circuit
Figure 13 (below) -This graph, called the polarization curve, gives an idea of how much power
the MFC can output to a device.
Polarization Curve
Figure 6 : Photograph of fully assembled One Gallon MFC
Power Management
• Because MFCs do not produce power and voltage sufficient enough to power desirable devices, such as wireless transmitters, a circuit design is necessary to boost the output power
• Simulations were used to find the effectiveness of the ciruit (shown below)
Figure 7 (left) - Schematics
of the Power Management
Circuit (PMC). The MFC is
simulated as a voltage source
in series with a resistor. The
other components are place
in accordance with the specifications of the data sheet.
The value expected for the
Low-dropout regulator (LDO)
is the nominal value of 2.2V,
which would be enough to
power any small device connected to it.
Carbon Nanotube Anode
• As certain types bacteria respi- • Typically, platinum and silver are
rate, they release electrons
used as electrode for the anodes
• With a semi-permeable memof MFCs
brane between the chambers of • Carbon nanotubes (CNTs) are a
the MFC, the electrons can travel cheaper, organic alternative for
from the anode to the cathode
the current MFC electrodes
• This transfer of electrons cre- • Stainless steel mesh was a backates a current and can be used
bone for the CNT’s growth and
to power devices
provided structure to the MFC
Figure 2 (below): Basic concepts of an MFC [3]
Figure 3 (far right): Carbon nanotube models
One Gallon MFC
Development
Data Acquisition
and Analysis
• Polarization curves show the highest amount of power that the MFC produces by varying the load values and recording the voltage
Conclusions and
Future Works
• One gallon MFC was successfully planned and created
• Tests on 50 mL MFCs showed that activated sludge is a better incoculum
than regular wastewater
• Currently, power output from 50 mL MFC and circuit is not high enough to
run useful devices
• Future experiments will be run directly on the one gallon MFC to determine
its power output and polarization data
Figure 8 (right) - Ideal results of
the LTC3105 operation. The input
voltage, Vin, remains constant
during the whole simulation. The
LDO voltage reaches its nominal value, 2.2 V, as expected. The
output voltage, Vout, reaches the
expected value calculated by the
ratio of the resistors, 3.3V. On this
simulation there was not a load
resistor connected to the output;
therefore, the results show a efficiency near the 100% as the current output would be 12mA, which
is the maximum value that the
LDO output can produce.
Acknowledgments
Figure 9 (left): Expected results
of the MFC simulation made on
LTSPICE. The input voltage, Vin,
slightly varies during the whole
simulation. The LDO voltage
reaches a maximum value of 2.2
V which is the nominal value.
As expected, the output voltage, Vout, is near 3.3 V and the
current that the load receives is
near 220mA. Low efficiency is expected because of the low input
and the high output resistance
that the MFC has.
This work was supported by Dr. Arum Han (Department of Computer and Electrical Engineering) and Dr. Choongho Yu (Department of Mechanical Engineering).
Support was given by graduate students, Celal Erbay, Salvador Carreon, Woongchul Choi,
and Mi-Jin Choi. Wastewater samples provided by Carter Creek Wastewater Treatment
Plant.
References
[1] NAEP, . Aeration tank. 2011. Photograph. National Association of Environmental Professionals, College Station, TX. Web. 16 Apr 2013. <http://
naep.tamu.edu/ccwwtp>.
[2] NIAID, . S. aureus bacteria.. 2012. Photograph. Medical XpressWeb. 16 Apr 2013. <http://s.ph-cdn.com/newman/gfx/news/hires/2011/thebestwaste.jpg>.
[3] MFC Diagram. 2010. Graphic. BioVolt: Calvin College Senior DesignWeb. 16 Apr 2013. <http://http://www.calvin.edu/academic/engineering/senior-design/SeniorDesign09-10/team01/web/-cdn.com/newman/gfx/news/hires/2011/thebestwaste.jpg>.
[4] Model of bucky ball (fulleren) and carbon nanotubes. 2010. Graphic. Swiss Nanoscience Institute, Fondo. Web. 16 Apr 2013. <http://www.nanoscience.ch/nccr/nanoscience/pictures/gallery_01/gallery_01_03>.