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.

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DC

V (

mV

)

Time (hours)

MFC Batch Studies – Voltage

DCV No HA

DCV with 40mg/L HA

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Cr(

VI)

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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.

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Cr(

VI)

concentr

ati

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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

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Cr(

VI)

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g/L

Time

Cr(VI) Reduction Rate Studies with MR-1

Cr(VI) no HA

Cr(VI) with 60 mg/L HA