Introduction
• A typical fuel cell converts chemical
energy to electrical energy but requires
the use of expensive catalysts to drive the
reaction.
• Microbial Fuel Cells (MFCs) make use of
bacteria as a biocatalyst eliminating the
need for expensive catalysts.
• MFCs have a wide range of applications
including wastewater treatment, ground
water remediation, leachate treatment,
bio-sensing, as well as deep ocean and
space exploration.
• The electrons generated in the MFC redox
reaction can be used to reduce heavy
metals found in groundwater
University of Southern California, Undergraduate Symposium for Scholarly and Creative Work, April 30 - May 1, 2013
Microbial Fuel Cell Technologies for Remediation of Hexavalent Chromium
in Groundwater Undergraduate Research Students: Peter Grasso, Kirsten Rice
Graduate Research Student: Ryan Thacher
Faculty Advisor: Professor Massoud Pirbazari
Background • Approximately 30% of California’s
drinking water comes directly from
groundwater.
• CrVI is an EPA priority pollutant and a
known carcinogen.
• CrVI is prevalent in California’s aquifers
• MFCs can treat polluted groundwater
by reducing CrVI (highly toxic and highly
soluble) to CrIII (less toxic and less
soluble).
• CrVI is a waste product from the leather
tanning, and electroplating industries.
0
1
2
3
4
5
6
7
8
0 24 48 72 96 120 144 168 192 216 240
DC
V (
mV
)
Time (hours)
MFC Batch Studies – Voltage
DCV No HA
DCV with 40mg/L HA
0
1
2
3
4
5
6
7
0 24 48 72 96 120 144 168 192 216 240 264
Cr(
VI)
Concentr
ati
on (
mg/L
)
Time (hours)
MFC Batch Studies - Cr(VI) Concentration
Cr(IV) with 40 mg/LHA
Cr(VI) no HA
Discussion
Summary
Micrograph of a Carbon Sponge Electrode Micrograph of an electrode with MR-1
Biomass
Research Results
Public Water Supply Wells in California
with CrVI presence
• Carbon dioxide, electrons, and protons are generated in the
anode.
• Electrons and protons are used in the cathode to reduce CrVI to
CrIII
• Proton exchange membrane (PEM) allows for the passage of
protons across compartments.
• Anaerobic conditions are required.
Anode Reaction C3H6O3 + 3H2O 3CO2 + 12e- + 12H+
Cathode Reaction: HCrO4- + 7H+ + 3e- Cr3+ + 4H2O
• The ability of an MFC to reduce
Cr decreases with increased
amounts.
• MFCs can be successfully used
to remediate polluted ground
water in a cost-effective
manner.
• Humic acids aid in the electron
transport process.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384
Cr(
VI)
concentr
ati
on (
PPB)
Time (hours)
Continuous Flow Column Studies
Cr(VI) No HA
Cr(VI) with 40mg/L HA
Figure 2. MFC Voltage output during Chromium reduction batch studies This studies took
place in dual-chambered microbial fuel cells pictured above. As in the rate reduction
studies 40 mg/L of HA were used in one of the samples. Voltage change was tracked
every 5 minutes for over 240 hours and periodic injections of a chromium solution took
place.
Figure 3. MFC chromium reduction batch studies.
CrVI concentrations were periodically recorded over the time length of the studies.
Figure 4. Chromium removal profiles in a dynamic continuous flow system.
Dual chambered microbial fuel cell Figure 1. Chromium rate studies with Shewanella MR-1 bacteria showing
the effect of natural organic matter (NOM) in chromium reduction.
Humic Acid Molecule
Future Research
• Wastewater as a fuel source
• Optimize MFC design to increase columbic
efficiency
• Investigate the reduction of other toxic metals (i.e.
U(VI))
• Address MFC system scale-up issues
• Optimize use of newly designed and fabricated
MFCs
e- e-
12 mL/hr
12 mL/hr
Silica
Sand
Column
Diagram of continuous flow dynamic system
12 mL/hr
Waste
• CrVI concentration was significantly decreased in the presence of MR-1
bacteria.
• The MFCs retained a greater concentration of CrVI as the experiment
progressed attesting to the reduction capabilities of the MFC.
• In the continuous flow dynamic studies the MFCs were able to effectively
reduce CrVI below the current national MCL standard for an extended period
of time.
• Experiments with NOM present resulted in better chromium removal in all
cases.
Nanowires connecting
MR-1 Bacteria
N2 Diffuser
Carbon Fiber
Electrode
Proton Exchange
Membrane
Biofilm Growth
e-
e- e-
e-
H+
Anode Cathode
Research Objective: To investigate the capabilities of Shewanella MR-1 bacteria in the reduction of CrVI
present in groundwater sources. Humic Acid was included in one of the MFCs in order to accurately model the
ubiquitous presence of natural organic matter within groundwater sources.
An example of a membrane bound
protein responsible for extracellular
electron transfer.
Acknowledgements
We would like to thank the National Science Foundation
for providing partial support for this project
0.000
1.000
2.000
3.000
4.000
5.000
6.000
0 20 40 60 80 100 120 140 160 180 200
Cr(
VI)
Concentr
ati
on m
g/L
Time
Cr(VI) Reduction Rate Studies with MR-1
Cr(VI) no HA
Cr(VI) with 60 mg/L HA