Microbial Fuel Cells Keith Scott

CONTENTCONTENT Fuel Cells and Biological Fuel CellsFuel Cells and Biological Fuel Cells Mechanisms Mechanisms Research ChallengesResearch Challenges MFC performanceMFC performance MFC prospectsMFC prospects

H2

H+C

athod

e (Pt catalyst)A

nod

e (P

t ca

taly

st)

O2

H2O

e-

2H2 4H+ + 4e- 4H+ + 4e- + O2 2H2O

The simplest realisation – the H2/O2 fuel cell

Pt Pt

Ele

ctro

l

yte

The electrolyte can be liquid, solid or polymeric and essentially:Separates fuel and oxidant•Facilitates ion transport between anolyte and catholyte•Prevents electrical short circuit between anode and cathode

Positively charged ions to pass through the electrolyte. The negatively charged electron must travel along an external circuit to the cathode, creating an electrical

current.

FUEL CELLGrove Genesis 1839 - 1842

Biological fuel cellsEnzyme and whole cell catalysis

Enzymatic fuel cellsUse isolated and purified enzymes to act as specific catalysts

Microbial fuel cellsUse whole living cells to continously supply the biocatalysts

R

ANODE CATHODEGluconicacid

e-

H2O

e-

Glucose

FAD

PQQ

e-

O2

COx

Cytc

e-e-

Bioelectrochemical energy generation

R

ANODE CATHODECO2

e-

H2O

Acetate

e-

O2

e-

Micro-organism

- better defined system- poisoning- reaction pathways more difficult

- more robust- oxidizing substrate completely- mixed substrates

MFC ApplicationsMFC Applications

Enhanced Water and Waste Enhanced Water and Waste treatmenttreatment

Energy ProductionEnergy Production Hydrogen GenerationHydrogen Generation Alternative Reductions- e.g. Alternative Reductions- e.g.

production of peroxideproduction of peroxide Alternative oxidations- using Alternative oxidations- using

electron accepting electron accepting (cathodic) bacteria(cathodic) bacteria

MFC- A Complex SystemMFC- A Complex System• Anode-attached

and suspended biomass

• Several metabolic types

• Multiple biological, chemical and electrochemical reactions

• Reactions occur in the bulk liquid, the biofilm and the electrode surface

Substrate

Bacteria

An

od

e

Oxygen

Me

mb

ran

e

Ca

tho

de

A

Biofilmcells

e-

rE

P

S

MRED

MOX

rB

Electrical mod

Boundarylayer

Substrate

Bacteria

An

od

e

Oxygen

Me

mb

ran

e

Ca

tho

de

A

Biofilmcells

Ele

ctr

och

em

ical

mod

el

anaerobic

Bulk liquid Biofilm

e-

rE

e-

rE

P

S

MRED

MOX

rB

P

S

MRED

MOX

rB

Electrical Electrical load

Boundarylayer

Aerobic

Performance limitationsR

ANODE CATHODE

substrate

products

O2

e-

P

S

1

2

e-

H+

3

4

H+65 7

9

8

e-

10

1 2 substrate and mediator transport (bulk, boundary layer, biofilm)

3 anodic reaction

4 electrical resistance

5 H+ transport(bulk, b.l., membrane)

67

8 9 oxygen transport (bulk, b.l.)

10 cathodic reaction

Microbial fuel cells: Biology/Chemistry/Physics

catalysts for the ORR:- Pt/C, high cost detrimental- few non-platinised catalysts- MnOx/C

O2 + 4H+ + 4e- → 2H2O

Research ThemesResearch Themes Anode materials – carbons (WC,…) Anode materials – carbons (WC,…) Biofilm mechanisms and anodophiles- Biofilm mechanisms and anodophiles- Geobacteraceae, Geobacteraceae,

Desulfuromonaceae, Alteromonadaceae, Desulfuromonaceae, Alteromonadaceae, Enterobacteriaceae, Pasteurellaceae, Clostridiaceae, Enterobacteriaceae, Pasteurellaceae, Clostridiaceae, AeromonadaceaeAeromonadaceae, and , and Comamonadaceae Comamonadaceae are able to are able to transfer electrons to electrodes. transfer electrons to electrodes.

Cathodes (activated carbons, porphyrins, MnOx, Cathodes (activated carbons, porphyrins, MnOx, biological……)biological……)

Separators (Tyvek, Scimat, Entek, ptfe.. )Separators (Tyvek, Scimat, Entek, ptfe.. ) Electrode structure (gas diffusion, ptfe bonded…)Electrode structure (gas diffusion, ptfe bonded…) Parameters (Temp, pH, COD, HRT, conductivity)Parameters (Temp, pH, COD, HRT, conductivity) Cell design (anode structure, scale-up, flow through)Cell design (anode structure, scale-up, flow through) ModellingModelling

1. Product electron transfer

Poxe-Iox

IredSred

Sox

Pred

2. Direct electron transfer

e-

Iox

IredSred

Sox

Microbial Fuel Cells: Mechanisms of electron transfer

cytochromes

3. Newer hypotheses for direct transfer

e-

Sred

"nano-wires"

Iox

Ired

Sox

metal oxides

e-

Sred

Iox

Ired

Sox

Microbial Fuel Cells: Mechanisms of electron transfer

4. Mediated electron transfer

Mred

Mox

e-

Sred

diffusiveIox

Ired

Sox

Microbial Fuel Cells: Mechanisms of electron transfer

M

e-

non-diffusiveIox

IredSred

Sox

mediator

mediator

AminoacidsFatty acidsGlucose

VFAs Acetic

e-

MetanoCO2 + H2

CarbohydratesLípidsProteins

+

ANODOPHILIC OXIDATION

METHANOGENESIS

METHANOGENESIS

ACIDOGENESIS

ACETOGENESIS

Extracellularenzymes

ANODOPHILIC OXIDATION

+ CO2 + H+

HYDROLYSIS

Faster at temperatures above 30ºC

Faster at temperaturesbelow 10ºC

COD REMOVALMicrobial Fuel CellsMicrobial Fuel Cells

Biofilm on graphite cloth

Biofilm on graphite paper

What is the biofilm area?

Biofilms on anodes

What is the anode area?

Biofilm on reticulated vitrouscarbon

Biofilms on anodes

Biofilm surface on graphite

Microbial Fuel CellsMicrobial Fuel Cells Cathode Material Cathode Material

Pt and metal phthalocyanine on KJB;. (Passive electrode without air sparging, catalyst loading 1 mg/cm2, 50 mM phosphate buffer with nutrients, pH=7.0, T= 30 oC, scan rate 1mV/s

Linear sweep voltammetry of O2 reduction: Iron phthalocyanine supported on KJB (FePc-KJB) carbon Iron phthalocyanine supported on KJB (FePc-KJB) carbon demonstrated higher activity towards oxygen reduction than Pt in neutral media. demonstrated higher activity towards oxygen reduction than Pt in neutral media.

Microbial Fuel cell Power Microbial Fuel cell Power Cathode Material Cathode Material

MFC polarisation and power density- With FePc-KJB as the MFC cathode With FePc-KJB as the MFC cathode catalyst, a power density of 634 mW m-2 which was higher than that obtained catalyst, a power density of 634 mW m-2 which was higher than that obtained using the precious-metal Pt cathode. Using a high surface area carbon brush using the precious-metal Pt cathode. Using a high surface area carbon brush anode the power density was increased to 2011 mW manode the power density was increased to 2011 mW m-2-2..

Current density J/mA cm-2

0.0 0.1 0.2 0.3 0.4

Cel

l vol

tage

V/V

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Pow

er d

ensi

ty P

/mW

m-2

0

200

400

600

800

1000FePc-KJBPt (in house)CoTMPP-KJBPt (commercial)

Various cathode catalysts (50 mM phosphate buffer, T= 30 oC).

FePc catalyst cathode and a graphite brush (30 oC,

200 mM PBM, pH 7.0, 1 g L-1 acetate).

Current density J/mA cm-2

0.0 0.2 0.4 0.6 0.8 1.0

Cel

l Vol

tage

V/V

0.0

0.2

0.4

0.6

0.8

1.0

Pow

er d

ensi

ty P

/mW

m-2

0

500

1000

1500

2000

2500

CARBON FELT CARBON BRUSH

Microbial Fuel cell Power from Wastewater

Cathode Material

COST ( 0.1 mg/cm2 Pt. 1.0 mg/cm2 Mn)

Mn: 0.02 $ g-1

Pt: 23 $ g-1

0.2 $ m-2 MnOx/C23 $ m-2Pt/C

Packed Bed of Graphite Granules anode. Variation of current with time for electrochemically-

active bacterial enrichment of SCMFC

The first 8 batches were performed with anaerobic sludge as inoculum (0.5% by volume) and AW (1000 ppm COD). The 9th batch was performed with AW containing 1000 ppm as COD and no inoculum. Anode cross sectional area: 12.5 cm2. External resistance: 500 Ω.

MFC PerformanceMFC Performance Continuous OperationContinuous Operation

MFC generate electricity from full-MFC generate electricity from full-strength brewery wastewaterstrength brewery wastewater

(2,239 mg-COD/L, 50mM PBS added) with the maximum power density of 483mW/m2 (12W/m3) at 30C and 435mW/m2 (11W/m3) at 20C, respectively- Y Feng et al WST 2008

Trickle Flow Tower ReactorTrickle Flow Tower Reactor

Effect of the loading rate on the SCMFC performance. Rext 100 Ω.

Complex System- Use models to better understand behaviour

Liq

uid

Bio

film

Ele

ctro

de

Solu

te

con

cen

trati

on

distance

diff.adv.

react.diff.adv.

react.react.diff.

Biofilm thickness

Here we measure!

Substrate

ProductElectrochemical product

Electrochemical reactant

Biofilm model Biofilm model (solutes)(solutes)

Model - biofilm+suspended cells and mediator

Microbes meet with resistanceMicrobes meet with resistance• The biochemical model is

based on the IWA anaerobic digestion model with electrogenic acetate oxidation and an electron-transfer mediator

Glucose

Propionate

Val/Butyrate

Acetate H2

CH4

AcidogenesisXsug

AcetogenesisXpro Xbv

MethanogenesisXace Xh2

CO2

MOX

MRed

current

ElectroactiveXeab

anode

Glucose

Propionate

Val/Butyrate

Acetate H2

CH4

AcidogenesisXsug

AcetogenesisXpro Xbv

MethanogenesisXace Xh2

CO2

MOX

MRed

current

ElectroactiveXeab

anode

Batstone D.J., Keller J., Angelidaki I., Kalyuzhnyi S.V., Pavlostathis S.G., Rozzi A., Sanders W.T.M., Siegrist H., Vavilin V.A. (2002) Anaerobic Digestion Model No. 1 (ADM1), IWA Task Group for Mathematical Modelling of Anaerobic Digestion Processes. London: IWA Publishing.

Integrating modeling and experimentationIntegrating modeling and experimentationExamining effect of external load on MFC properties

0

50

100

150

200

250

300

350

400

450

500

0 5 10 15

Time (days)

Org

anic

s in

bul

k (g

CO

D/m

3 )

0

0.5

1

1.5

2

2.5

3

3.5

4

H2

in b

ulk

(mgC

OD

/m3 )

Glu

CH4

Ace

Pro

But

H2

0

5

10

15

20

25

30

35

40

0 5 10 15

Time (days)

Cu

rre

nt

de

nsi

ty,

j (m

A/m

2)

0

5

10

15

20

25

30

To

tal c

ha

rge

(C

)Currentdensity

Charge

Model outputsTime-dependent production of Current , VoltageTime-dependent bulk substrate, intermediate and product concentrationsPower, Coulombic yieldsCurrent-voltage, current-power curvesSpatial distributions of chemical speciesSpatial distributions of biomass species

• Qualitative predictions

• Increasing external resistance should reduce the rate of electron transfer from the substrate to the anode

• Electrogens become less competitive

• Methanogens become more competitive

• Reduced current/charge and Coulombic yield

• Community composition should alter with external resistance

• Biomass of electrogens should be reduced

Integrating modeling and experimentationIntegrating modeling and experimentation

Effect of external resistance on COD removalEffect of external resistance on COD removal

Time (days)

CO

D (

g/m

3)

0

100

200

300

400

500

600

0 2 4 6

COD (exp), 0.1 K (1)

COD (exp), 0.1 K (2)

COD (sim), 0.1 K

COD

• Experimental 100 Ohms

Effect of external resistance on COD removalEffect of external resistance on COD removal

0

10

20

30

40

50

60

70

80

90

100

0.1

kohm

s

1 ko

hms

10 k

ohm

s

25 k

ohm

s

50 k

ohm

s

OC

V

cont

rol

CO

D r

emov

al (

%)

• Higher external load shows reduction in COD removal efficiency detected experimentally

• Systems run as MFC have improved COD removal compared to controls

• Denaturing gradient gel electrophoresis of anode communities

Effect of external resistance on the anode communityEffect of external resistance on the anode community

M I 100 1000 M 10000 25000 M 50000 OCV M Cont.

• Anode bacterial communities developed at 100 to 50,000 ohms characterized

• Anode biomass harvested at end of experimental run

• DNA extracted and 16S rRNA gene fragments amplified by PCR

• 16S rRNA gene fragments analyzed by DGGE to provide a community fingerprint

• External load has profound effects on the anode community and MFC performance

• Even if MFC never produce useful amounts of electricity, still potential benefits for wastewater treatment

• Can external load be used to “tune”

• Treatment performance?

• Sludge yield?

• If lower external load selects for electrogens, should MFC anode communities be conditioned under low external load to maximize electrogen colonization?

Prospects for wastewater MFC and Prospects for wastewater MFC and biological treatmentbiological treatment

PROSPECTSPROSPECTSThe key issues for a microbial (bio-electrochemical) fuel The key issues for a microbial (bio-electrochemical) fuel

cell reactor for the recovery of energy or production of cell reactor for the recovery of energy or production of valuable chemicals relate to:valuable chemicals relate to:

Reactor Cost (in relation to product value including Reactor Cost (in relation to product value including wastewater treatment) wastewater treatment)

MFC Reactor DesignMFC Reactor Design Reactor scale-up to suitable plant production sizeReactor scale-up to suitable plant production size Reactor DurabilityReactor Durability

ANODE DESIGN and CONFIGURATION CRUCIALANODE DESIGN and CONFIGURATION CRUCIAL WasteWater polishingWasteWater polishing

Biogas kWh

Wastewater treatment Anaerobic digestion MFC

Biogas kWh

Wastewater treatment Anaerobic digestion MFC

Reactor CostReactor Cost If we take a potential power capability ofIf we take a potential power capability of 1.0 kW per m1.0 kW per m33 of reactor of reactor

containing 100 cell equivalents giving power of 10 W/mcontaining 100 cell equivalents giving power of 10 W/m22 of cross- of cross-sectional area. sectional area.

The energy produced would be 8000 kWh/year with a value of The energy produced would be 8000 kWh/year with a value of approximately £800/year.approximately £800/year.

Working on a simple payback over 5 years this would be Working on a simple payback over 5 years this would be equivalent to a cost from generating electricity of £4000.equivalent to a cost from generating electricity of £4000.

Thus the cost of an individual cell would be of the order of £40 (/mThus the cost of an individual cell would be of the order of £40 (/m22).).

These are quite challenging costs and rule out the use of precious These are quite challenging costs and rule out the use of precious metal (including silver)metal (including silver) for catalysts and ion-exchange membrane for catalysts and ion-exchange membrane materials that are frequently used in microbial fuel cells. materials that are frequently used in microbial fuel cells.

AcknowledgmentsAcknowledgments

EU Marie Curie ToKEU Marie Curie ToK EPSRC EPSRC Northumbrian WaterNorthumbrian Water Research Group- Profs I M Head, T Curtis Dr E YuResearch Group- Profs I M Head, T Curtis Dr E Yu Drs K Katuri, M Di Lorenzo , I Roche, M Drs K Katuri, M Di Lorenzo , I Roche, M

Ghangreghar, B Erable, N Duteanu, Y FengGhangreghar, B Erable, N Duteanu, Y Feng PhDs- Amor Larrosa Guerrora, Jamie Hinks, PhDs- Amor Larrosa Guerrora, Jamie Hinks,

Sharon Velasquez Orta, Beate ChristgenSharon Velasquez Orta, Beate Christgen