Microbial Fuel Cell and Wastewater Treatment

Tom Curtis and Colleagues

Newcastle University, UK

Northumbrian Water Ltd, UK

Inexorable Rise of Energy Use in The Water Industry

Inexorable Rise in Energy Prices

But there is Energy in Wastewater!

• Bomb Calorimetry

• Domestic wastewater contains

– 7.6 kJ/L

– 2000 kWh/ML

• Probably more..

Heidrich 2011

Electro-genesis

Electro-genesis

Anaerobic breakdown of complex wastes

Domestic wastewater treatment in methanogenic reactors

Works well in S. America

– No 1o sedimentation tank

– Little sludge

– Lots of methane

– Up to 600,000 people

• Key interlinked problems

– Temperature

– Stability

– Nutrients

UASB treating domestic wastewater in NE Brazil

-5.0E+05

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

4 8 15

Po

pu

lati

on

(ce

ll m

l-1)

Temperature (oC)

Methanogenic taxa dominance

MMB

MSC

MST

1.86

2.25

3.04

y = 1.5688e0.0442x R² = 0.9991

0

1

1

2

2

3

3

4

0 5 10 15 20

Spec

ific

rat

e (f

emto

mo

lsC

H4 c

ell-1

d

ay-1

)

Temperature (oC)

Specific methanogenic activity

specificmethanogenicrate

0.005

0.011

0.014

y = 0.0037e0.097x R² = 0.8154

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0 5 10 15 20

Spec

ific

rat

e (f

emto

mo

ls C

H4 c

ell-1

) day

-1)

Temperature (oC)

Specific hydrolytic activity

Specific hydrolysis rateExpon. (Specific hydrolysis rate)

a) Methane production versus time at all temperature; b) Methanogenic populations at all temperatures (the trend shows that the lower the temperature the higher the hydrogenotrophic:acetotrophic ratio – hydrogenotrophic methanogenesis is supported at low temperatures; c) Specific methanogenesis rates; d) specific hydrolysis rates; all images above describe anaerobic digestion of raw domestic wastewater at 4, 8 and 15oC.

A Microbial Fuel Cell

A MFC is a device that uses bacteria to oxidize organic matter and produce electricity. The bacteria (attached to the anode) produce electrons that travel to the cathode (current).

Proton Exchange membrane

load

Anode Cathode

bac

teri

a

Oxidation products

(CO2)

Fuel (wastes)

e-

e-

O2

H2O

H+

This is how a MFC works

Source: Liu et al., Environ. Sci. Technol., (2004)

H2

Cathode

CO2 e-

H+

e-

Bacteria

Anode

PEM

No oxygen in cathode chamber

PS

O2

Ref: Liu, Grot and Logan, Environ. Sci. Technol. (2005)

No oxygen in anode chamber

0.25 V needed (vs 1.8 V for water electrolysis)

A Microbial Electrolysis Cell

Anaerobic technologies for wastewater treatment

MFC MEC Anaerobic Digestion

Temperatures 7.5 – 45 oC 4.5 – 40 oC > 20 oC

Process control

limited possible limited

Retrofittable unlikely possible possible

Organic Load low- high low - high high

Why retrofitting is important

• Pie chart of your water bill

– 30% Water

– 40% Wastewater

– 30% Financing cost:

• 25 years for fixtures

• 50 years for concrete!

1980 1985 1990 1995 2000 2005 20100

20

40

60

80

100

Was

tew

ater

tre

atm

ent

rate

(%

)

Year

Urban wastewater

Urban domestic wastewater

Municipal Wastewater Treatment Rates In China

Most Research is Small Scale

Sampling port

Chamber filled

with solution

(b)

ANODE

(carbon paper) Cathode

4 cm

Catalyst

PEM (Nafion)

Diffusion layer: - Reduces water loss

- Increases CE due to reduced O2 transfer into anode chamber

Most Research is Small Scale

Sampling port

Chamber filled with solution (b)

ANODE

(carbon paper)

The PEM can be omitted, increasing power generation

Cathode

4 cm

Catalyst

Ammonia-gas treatment of anode increases power

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1

Current density (mA cm-2

)

Ce

ll V

olta

ge

(V

)

0

500

1000

1500

2000

Po

we

r d

en

sity (

mW

m-2

)

V-Treated

V-UntreatedP-Treated

P-UntreatedPower = 1970 mW/m2 (acetate) = 115 W/m3

Where are the microbes in a Microbial Fuel Cell?

Thick biofilm on wastewater fed microbial fuel cell

• Microbes accept electrons from organic matter – Electron donors

• Microbes donate electrons to reducible chemicals – Electron Acceptors

• e.g. oxygen

• Iron (oxides)

• In MFC anode is an electron acceptor

• Microbe breath anode!

Maturing anode community increases current

Voltages are modest

• Anode – Acetate oxidation

• 2HCO-3 + 9 H+ + 8e- => CH3COO-

+4H2O – -0.300V

• Cathode – Oxygen reduction

• O2 + 4 H+ + 4 e- 2 H2O – 0.805V IN THEORY

– ~0.200V In practice

E’emf = 0.200-(-300)= 0.500V

Power is increasing year on year

• Power increasingly expressed / m3

• May also / m2

– Anode

– Cathode

– Membrane

Logan & Regan, 2006. Trends in Microbiology. 14, 512-518

Most Researchers “cheat”

• Use – Acetate or sucrose instead of wastewater

– Warm rooms instead of ambient

– High conductivity buffer instead of wastewater

– Expensive materials instead of cheap ones

– Short runs at small scale instead of long ones at large scale

Research Challenges in Newcastle

• Scale

• Materials

• Coulombic efficiency

• Length of operation

• Valorisation

• Retrofitability

Rozendaal TIB 2008

Tentative costs WWT: anaerobic and MEC look best.

System Product Capital costs

(Euros/kg

COD)

Product

Revenue

(Euros/kg

COD)

Net

Revenue

(Euros/kg

COD)

Activated

sludge

N/A 0.1 -0.3 -0.3

Anaerobic

Digestion

CH4 0.01 0.1 0.1

MFC Electricity 0.4 0.2 -0.2

MEC H2 0.4 0.6 0.2

Rozendaal TIB 2008

Table1:Cost-performanceratioforthedifferentmembranematerials.Costwaslinkedto

powerdensityandcoulombicefficiency.

Cost/£m-2

P/mWm-2

Cost/P£mW-1

CE/%

Cost/%CE/£m-2%-1

Energygenerated

overalifetimeof10

years/kWhm

-2

Totalincome

generatedover10

years/£

CP 105 24±0.02 4.4 68±11 1.5 2.1 0.17RH 1.5 14±2.2 0.11 63±8 0.02 1.2 0.10Nafion 506 29±2.6 17.5 71±12 7.1 2.5 0.20

ETFE 3 29±3.4 0.10 92±6 0.03 2.5 0.20PVDF 2 11±0.5 0.18 66±20 0.03 1 0.08

Materials: Evaluation on Cost vs Performance

Christgen 2013

Less Current From Complex Wastes

Hydrolysis the rate limiting

Distinct communities

MEC performance on real wastes

• Research remains sparse, energy recovery often not reported, widely variable.

Paper Substrate Reported Energy recovery

Ditzig 2007 Domestic wastewater < 1%

Wagner 2009 Swine wastewater 179%

Cusick 2011 Winery wastewater (acetate supplement)

If methane yield used “energy would exceed electrical input”

Escapa 2012 Domestic wastewater

“energy consumption comparable to aerobic treatments”

Jia 2012 Piggery wastewater Input electricity efficiency 124% - term not defined

Low Yields imply large energy losses: possible uncoupling

Figure 6a: Biomass yield under different loads, OCV and control

0.1k ohms 1k ohms 10k ohms 25k ohms 50k ohms OCV Control

Bio

ma

ss y

ield

(g

VS

S/g

CO

D r

ed

uce

d)

0.00

0.05

0.10

0.15

0.20

Katuri 2007

Losing energy in the food chain?

Polymers

Monomers

Electrons

Two: Seeds, temperatures + feeds

Arctic soils UK wastewater

Lise Øvreås

Temp and seed: little effect Feed: big effect

16

0

20

8

40

60

2040

06080

Coulombic efficiency (%)

Power density (mVm2)

COD removal (%)

acetate cold soil

acetate cold w w

acetate w arm soil

acetate w arm w w

w astew ater cold soil

w astew ater cold w w

w astew ater w arm soil

w astew ater w arm w w

C2

Electro-genesis

Electro-genesis

Anaerobic breakdown of complex wastes

Acetate diversity: not a subset of wastewater diversity

.

0

2

4

6

8

10

12

14

16

Acetate Wastewater

Lo

g e D

ive

rsit

y

Bigger Trials

Worst conditions

• Heath Robinson design

• Low load

• Low temperatures

• Cheap materials

Energy recovery – Encouraging

0.00

20.00

40.00

60.00

80.00

100.00

120.00

Inp

ut

en

erg

y re

cove

ry (

%)

May June July August September October November

Heidrich et al., 2012

It’s the first time I have analysed the up-to date data - it does seem to be reducing in performance as we move from the summer (water temperature of 15- 20°C) to the winter (6-10°C). But even if it levels at 50% over the winter – with better design I’m sure it could be brought up – the main thing is its still working. The decline could also be due to time in operation – membranes clogging etc.

First Successful “Large” Trial

• Previous known failures – Warm climates

– Low conductivity

• Californian Vineyard – The temperature was 30°C, there was no membrane

and competitors to methanogens used the hydrogen

• Australian Brewery – It used reverse osmosis water and therefore the

wastewater had excesively low conductivity

Future Research: short term

• Suck it and see!

• Building 4 replicate pilot plants

• Improved hydrogen retention

• Improved cathodes

Long term: modelling

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

EPSRC Frontier! Long term multi-scale modelling with individual based foundation P

iciorean

u, C

., Head

, I.M., K

aturi, K

.P., van Lo

osd

recht, M

.C.M

., Scott, K

. (2

00

7). A

com

pu

tation

al mo

del fo

r bio

film-b

ased m

icrob

ial fuels cells. W

ater R

esearch 4

1, 2

92

1-2

94

0

Examples of Important work by other groups

• Animal wastes

– Lars Angenent

• Nutrient Removal

– Wetsus

• Novel applications

– Bruce Logan

• Novel cathode processes

– Korneel Rabaey

Summary • Wastewater contains 4 x more energy than required to

treat it.

• MEC one possible solution – Process fundamentals are obscure – Most “practical research” is unrealistic

• Progress needs:

– Cheap materials – Realistic Trials – Fundamental investigation leading to – New generation of models