Microbial Fuel Cell_3

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USCSC Geobiology

MICROBIAL FUEL CELLS (MFCs)

Biofuels for energy production and

Waste disposal

Provost’s Energy Retreat FEEI

February 24 & 25, 2006

Ken Nealson

Wrigley Professor of Geobiology

USC



Energy Flow on EarthEnergy Flow on Earth

Light

Energy

(178,000 TW)

Geothermal

Energy

(30 TW)

PS Bacteria

CyanobacteriaAlgae & Plants

Biomass

Organic C

Reduced

Inorganics

(organic C)

CO2Lithotrophs

Animals

FungiBacteria

CO2

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Biomass

Waste(CH4)

CH3OH 3/1

CH3CH2OH 2.5/1

Fermentation

Metabolism

Biofuels – methanol

ethanol



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Biomass

Waste

Biofuel

Cells

Electricity

CO2

Pollution removalwater purification

industrial water

industrial waste

Biofuel Cell Interruption of the process!

(Imagine many other fuels being used

by these Microbial Fuel Cells)

Don’t always have to “win”

breaking even might be enough!



USCSC Geobiology

What is a microbial fuel cell?

Advantages of MFCs

Disadvantages of MFCs

State of the Art

Challenges

Prospects

Demonstrate these withexamples of our work

when appropriate.



USCSC Geobiology

What is a Microbial Fuel Cell?

Fuel cell with microbe as a catalyst

Known since early 1900’s

First report of a microbial fuel cell in 1911 (Potter)

Take advantage of way life works:Take up fuel, extract electrons

electron flow to an acceptor is used to charge a

“biological capacitor”charged capacitor used to make biological energy

Fuel cell just short circuits this process

MFCs come in two types: mediated and mediator-less



Microbe

A n o d e

C a t h o d e

Fuel

Oxidized Fuel

= Oxidized Mediator

= Reduced Mediator

Load

Reduced Oxidant

Oxidant

= Ion Exchange Membrane

Mediated Fuel Cell

MicrobeA n o d e

C a t h o d e

Fuel

Oxidized Fuel

= Oxidized carrier molecule

= Reduced carrier molecule

Load

Reduced Oxidant

Oxidant

= Outer membrane electron carriers (i.e.nanowires)

= Ion Exchange Membrane

• Almost any microbe can produce electricitywith an electron shuttle (innefficient !)

• Mediators are mostly phenolic compounds,which are expensive & sometimes toxic

• A mediator-less microbial fuel cell ispossible if the microbes can give electronsdirectly to the electrode

• No additional electron shuttle isneeded

• Few known microbes have this

ability

• Shewanella & iron reducers do !

Mediator-less Fuel Cell

Two Types of Microbial Fuel Cells



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Mediator-less fuel cells take advantage of special bacteria

Isolated ~ 15 years ago -- Shewanella, Geobacter, othersIron/manganese reducing bacteria

Famous for reducing solid substrates (Fe & Mn oxides)

Subsequently found to have enzymes on outside of the cell

Unusual for bacteria, but necessary for this reaction

Example shown in next slide



Enrichment Culture Five Days Incubation

Pure Culture on MnO2 Breathing Mn oxide!

Solid Substrate

Biofilm



Microbial Fuel Cell

Used to evaluate strains in the laboratory

Anode – graphite with bacterial catalyst

Glass – autoclavable, re-usable

Extra ports for electrochemical measurementsCathode platinized graphite (Surya Prakash’s help!)

Pt coated graphite

felt electrodeScale in inches

Anode Cathode

Clamp holding ionexchange membrane

Graphite felt

electrode

Pt leads

Injectionport for

fuel

N2 inlet

N2 outlet Air outlet

Air inlet10 ohm

V



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Potential advantages of MFCs

1.Catalysts are inexpensive – essentially “free”

2.Catalysts are diverse and robust

extreme conditions of pH, Eh, T, salinity, etc.

3.Catalysts are versatile – single type can use

wide variety of substrates

4.Catalysts can self repair (proteins, DNA,

membranes, etc.)



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More than 50 different Shewanella species known

So far, all produce current

From ~ 4 oC to 55 oC; wide salinity range

65 different carbon sources

Very tough and robust organisms

Just the tip of the iceberg of biological diversity

(other Fe-reducers are known that grow to 110o

C!)



Response to different fuels

(Shewanella)

00.005

0.01

0.015

0.02

0.025

0.030.035

0.04

0.045

0.05

0 10 20 30 40

Time (hours)

C u r r e n t ( m A )

Lactate

LactateSuccinate

00.005

0.01

0.015

0.02

0.025

0.030.035

0.04

0.045

0.05

0 10 20 30 40

Time (hours)


Lactate

LactateAcetate

• MR-1 can grow by converting lactate to

acetate:

lactate→ pyruvate → acetate → CO2

• MR-1 can also use these products to

maintain and produce current

•Can also switch from one to another with ease:

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 5 10 15 20 25

Time (Hours)


LactateLactate

Formate

MFC OD of 0.8

MFC OD of 0.3 MFC OD of 0.3

(1mM)(1mM)

(1mM)

(1mM)

(1mM)(1mM)

(1mM)

(1mM)(1mM)

Acetate

Formate

Succinate



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Potential disadvantages of MFCs

1.Current density is low

2.Difficult to run and maintain

3.Sensitive to breakdown and decay

Almost certainly all these “disadvantages”are built on misconceptions

These arise from use of mediated MFCs



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State of the art:

1.Many bacteria now known that produce current inmediator-less MFCs

2.Mechanism of current production not understood

3.Current densities are getting into the range of interest – mA/cm2 (wide range of abilities)

4. Interesting development has to do with microbial

consortia – current density is always higher



USCSC Geobiology

Chang et al., 2006, Electrochemically

active bacteria (EAB) and mediator-lessmicrobial fuel cells. J. Microbiol. Biotechnol.

16:163-177.

Power densities range from: 16 to 4,300 mW/m2

I have a PDF of this I will send to anyone who

wants – reviews much of what I have said today.



USCSC Geobiology

Challenges to be addressed:

1.How do they work? Mechanisms?genetic and genomic approaches

2. Physiology of the cells – interface with FC

biofilms, etc.

3. Microbial communities and consortia

enrichment cultures



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9 mutants that knock out ability to produce current

4 are involved with iron reduction

5 are not –

3 mutants that increase current production

all of these are cytochromes leading to

other termini

Several regulatory mutants that increase or

decrease the level of current production





Table 1. Electrochemical activities of Shewanella oneidensis MR-1 and its mutants

StrainNo.

Gene

Growth1 on

Lactate/Fumarate

Max. current

(μA)

Coulomb3

(C) CV4

test

1 ΔluxSrif +++ 65.0±6.1 2.53±0.25 ++

2 Δ mtrA +++ 7.3±0.5 0.42±0.09 +

3 Δ omcA +++ 4.6±0.2 0.32±0.01 +/-

4 ΔhydB +++ 61.0±15.4 2.63±0.37 +

5

ΔhydB and

ΔhydA +++ 66.3±17.9 2.94±0.48 +

6 ΔhydA +++ 54.0±10.0 2.53±0.72 +

7 Δ tatC + 15.3±2.9 0.97±0.16 ++

8 Δmpw +++ 48.0±7.2 2.15±0.09 +

9 Δ fur ++ 26.0±2.0 1.30±0.25 +

10 Δ crp + 19.0±6.6 1.11±0.36 +

11 Wild type +++ 68.0±7.8 2.56±0.18 +

12 E.coli +++2 5.0±0.1 - -

G bi l



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How do the catalysts work?

Mutant screeninggenome of Shewanella has been sequenced

use this information to make directed mutants

mutant analysis identifies those genes

coding for proteins involved with current prod.

so far great success using this approach

G bi l



USCSC Geobiology

Understanding the catalyst:

Role of attachment, biofilms, connections

No doubt of catalytic abilityQuestion of how to control and direct it

This is issue of physiology of cells:

Shewanella oneidensis MR 1 biofilm current



Shewanella oneidensis MR-1 biofilm current

production

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30

Time (hrs)

C u r r e

n t ( m A )

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8

Time (Hours)

C u r r e

n t ( m A )

MR-1 Biofilm on Anode (4 day growth) Injection of planktonic cells (OD 0.8)

Graphite felt electrode without

MR-1

Graphite felt electrode with

planktonic MR-1 (OD 0.4)

Graphite felt electrode with MR-1

biofilm

Erroneous data point

Maximum current value ≈ 0.8 mA

Maximum current value ≈ 0.3 mA

Courtesy of PNNL and KIST

MR 1 biofilm/electrode images (PNNL)



MR-1 biofilm/electrode images (PNNL)

G bi l



USCSC Geobiology

Many questions to answer and

things to optimize

However, these approaches, coupled

with modeling should lead to an optimum

catalyst that can be combined withoptimum design to yield high power

To this end: we were just awarded a MURIFrom DOD for this work (5 from USC).

(Prakash,Ronney,Wang,Mansfeld, Nealson)

G bi l



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Prospects & Approach:

Understand the systemOptimize to produce adequate current

Scale up or down for specific applications:

power

waste disposal

remote power supplieswater treatment

etc.

Geobiology



USCSC Geobiology

MFC

Power

Production Waste

Disposal

Water

Treatment

Biosensors

RemotePower

Supplies

Medical

Devices

Teaching

Scale up

Scale down

Same scaleResearch tool

Geobiology



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Waste Disposal:

7 billion tons of sewage sludge generated

in the US

We estimate that 90% of this could be

metabolized by efficient MFC approach

If properly designed, we could get paidfor this process by current production

THANK YOU !!

Geobiology



USCSC Geobiology

MICROBIAL FUEL CELLS (MFCs)

Biofuels for energy production and

Waste disposal

THANK YOU FOR YOUR ATTENTION !!

Ken Nealson

Wrigley Professor of Geobiology

USC([email protected])

Geobiology



USCSC Geobiology



Microbial Fuel Cell OperationFuels Organic or

inorganic

matter

Ion ExchangeMembranes

Solid polymer or single

compartment reactor

Oxidant Atmospheric

oxygen

A n o d e C a t al y s t

C a t h o d e C a t al y s

t

P r o t onE x

ch an g eM e m b r an e

Fuel

OxidizedFuel

Oxidant

ReducedOxidant

Oxi d a t i on

R e a c t i on

R e d u c t i on

R e a c t i on

e-

e-

e-

e-e- e-e-e-

e-

e-

e-e-

e-e-

H+

H+H+ H+ H+

H+H+H+

H+

H+

H+

H+

Catalyst Microbe at

anode

Pt at cathode(soon to be

microbe)

Geobiology



USCSC Geobiology

A n o d e C a t a

l y s t

C

a t h o d e C a t al y s t

P r o t onE x ch an g e

M e m b r an e

Fuel

OxidizedFuel

Oxidant

ReducedOxidant

Oxi d a t i o

n

R e a c t i o

n

R e d u c t i on

R e a c t i o

n

e-

e-

e-

e-e- e-e-e-

e-

e-

e-e-

e-e-

H+

H+

H+ H+ H+H+H

+H+

H+

H+

H+

H+

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Microbial Fuel Cell_3