waste2watergy - pnsctapnscta.org/wp-content/uploads/2015/07/4-microbial... · 7/4/2015 · 24. 0...

Yanzhen Fan, Ph.D

Co-founder and CTO

Waste2Watergy LLC

Waste2Watergy1

Hurricane season

Hurricane Irma,center, with Hurricane Katia, left, and Hurricane Jose, right on Sept. 7, 2017

???

Hurricane Harvey on August 25, 2017Once in 1000 years

Hurricane Katrina on August 28, 2005The costliest natural disaster

Cost refers to total estimated property damage

Rank Hurricane Season Damage

1 Katrina 2005 $108 billion

2 Sandy 2012 $71.4 billion

3 Harvey 2017 >$70 billion*

Source: National Hurricane Center 2

Why so many, so much

3

CO2

CH4

What can we do?

4

Energy and Wastewater

The energy needs for a typical domestic wastewater

treatment plant employing aerobic activated sludge

treatment and anaerobic sludge digestion is 0.6 kWh m-3.

Wastewater treatment accounts for about 3% of electrical

energy consumed in developed countries, 15 GW in the

US.

Wastewater contains as much as 9.3 times the amount of

energy currently consumed to treat the water in a modern

wastewater treatment plant.

Energy in food processing wastewater = Energy in

domestic wastewater

5

Can we make wastewater treatment

Energy-neutral?Energy Positive?

6

Wastewater to Energy

Anaerobic digestion:

– Advantage:

Low capital cost and operational cost compared to aerobic process

High COD loading: 25 kg COD m-3d-1

High power: 1.1 kW m-3, based on an overall energy efficiency of 30%

– Disadvantage:

The removal of H2S from the biogas to prevent combustion-associated

byproducts is expensive and energy intensive.

Additional energy may be needed to strip CH4 from the effluent

Only available in medium to large scale

Slow start-up: 3-6 months

7

Wastewater to Energy

Microbial fuel cell

– How does an MFC work?

– Where can we find the electricity generating bacteria?

– How do electrons reach the electrode?

– Electrodes

– Designs of MFCs

– Scale-up

8

Electricity Production in a Microbial Fuel Cell (MFC)

An MFC is a device that directly converts chemical energy

into electricity through the catalytic activities of

microorganisms.

AnodeCathode

ba

cte

ria

Oxidation

products

(CO2)

Fuel

(organic

wastes))

e-

e-

O2

H2O

H+

This is how an MFC works

Cathode: O2 + 4 H+ + 4 e- = 2 H2OAnode: CxHyOz + H2O CO2 + e

- + H+

10

History of MFC

Connection between biology and electricity was discovered by Luigi Galvani in 1791

A half cell using microorganism (E. Coli) was demonstrated by Michael Potter in 1910

In 1960s, develop enzyme-based and mediator-MFCs as a possible technology for a waste disposal system for space flights

Early 2000-now, mediator-less MFCs for energy generation and wastewater treatment

.

11

Advantages over chemical fuel cell

Fuels– Toxic, explosive small molecules (H2, methanol) in

chemical fuel cells

– A diverse range of environmental fuels in MFCs;

Temperature– High temperature for chemical fuel cells

– Ambient temperature for MFCs

Catalyst– expensive catalysts for chemical fuel cells

– naturally occurring microorganism for MFC

12

5 µm

A

0.5 µm

C

10 µm

D

B

10

µm

SEM images of carbon fiber cloth anode surface (A) micro scale carbon fibers without bacterial

attached; (B) bacteria growth on a single carbon fiber; (C) detailed bacteria in this study; and (D)

Carbon cloth surface covered by thick biofilms

Electricity generating bacteria

Where - Electricity generating bacteria are abundant in natural

environment: wastewater, ocean sediment, digested sludge, etc.

13

How do electrons reach the electrode?

NADH+

NAD

BacteriumElectrode

eCarrier (oxidized)

Carrier (reduced)

BacteriumElectrode

ee

NADH+

NAD

BacteriumElectrode

Nano-Wire

e

ee

e e ee

(A) Electron transfer by mediators;

(B) Direct electron transfer through bacteria outer-membrane enzymes;

(C) Electron transfer via pilus-like nanowires

A B C

14

Scanning tunneling microscope (STM)

Gorby et al, 2006, PNAS15

Anode materials

Graphite granule

Reticulated Vitreous Carbon

Carbon cloth

Graphite fiber Activated carbonCarbon Paper

Graphite felt

16

http://www.theodoregray.com/PeriodicTable/Samples/006.20/index.s15.html

Basic requirements for electrode materials

Good conductivity

Acceptable physical strength

High surface area

Favorable surface properties

Good chemical and electrochemical stability

Low cost

17

Cathode materials

Good conductivity

Large surface area

Catalyst

Teflon (PTFE)

Support materialCatalyst layer

H+

e-

Air (O2)

18

Laboratory MFCs

B

CEA#

1

CEA#

2

Cathode of

CEA#1

Cathode of

CEA#2

19

Air-cathode MFC

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

Challenge: Low power density

• Electrode surface area

• Membrane

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200

Current density (mA/m2)

Pow

er

density

(m

W/m

2)

0

5

10

15

20

25

30

Voltage (

v)

B

26 mW/m2

20

Membrane-free air cathode MFC

PEM (Nafion)

(b)

Source: Liu & Logan, Environ. Sci. Technol. (2004)

Sampling port

CATHODE (carbon paper & Pt)

Chamber

filled with

solution

(a)

ANODE(carbon paper)

Cover of

anode

The PEM can be omitted, increasing power generation

0

100

200

300

400

500

600

0 500 1000 1500 2000 2500

Current desity (mA/m2)

Pow

er

density (

mW

/m2)

Power= 506 mW/m2

21

Advantages of using single chamber MFCs

Passive air can be used thus no aeration is

needed

Better cathode performance due to the high

oxygen concentration

Smaller cell volume, thus higher volumetric

power density, can be easier to achieve

22

Single chamber Membrane-free MFCs

(a) schematic of MFC (b) prototype.

Sampling portNafion (or w/o)

Carbon cloth

(cathode)

Chamber

Carbon

Cloth

(anode)

Cover of

anode

Functions of Membrane:

•Separate the anode and cathode

•Block oxygen

•Holding water

Disadvantages of using membrane:

•Membrane resistance

•Expensive (Nafion)

•Clogging

•Degradation

Source: Liu et al., Environ. Sci. Technol., (2004) 23

Disadvantages of Using Membrane-free MFC

Columbic efficiency (CE) is lower than that

with a membrane

CE: electron recovery as electricity

Anode and cathode distance is limited to a

certain range due to the negative effect of

oxygen

24

0

10

20

30

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1

Current Density (mA cm-2)

Coulo

mbic

Eff

icie

ncy (

%)

0 layer

1 layer

2 layers

3 layers

Source: Fan et al., Journal of Power Sources, (2007)

CathodeAnode

J-cloth

(B)

Cloth layers reduced the oxygen diffusion

Over 100% increase in CE at

0.6 mA/cm2

0

10

20

30

40

50

60

70

80

90

0 0.2 0.4 0.6 0.8 1

Current Density (mA cm-2)

Pow

er

Density (

W m

-3)

0 layer

1 layer

2 layers

3 layers

A slight decrease (7%) of power densities

25

Cloth electrode assembly MFC

CEA#1

CEA#2

Cathode of CEA#1Inlet

Outlet

Cathode of CEA#2

Cathode CathodeAnode

Cloth Cloth

( ─ ) ( + )


Anode: non-wet proofed carbon cloth

Cathode: 30% wet proofed carbon cloth coated with 0.5 mg/cm2 Pt

and PTFE

Cloth: J-cloth 26

0.1

0.2

0.3

0.4

0.5

0.6

0 0.5 1 1.5 2 2.5 3 3.5 4

Anodic current density (mA/cm2)

Vo

lta

ge

(V

)

1-7-200

1-7-200

2-7-200

2-7-200

3.6-7-200

3.6-7-200

7-7-200

7-7-200

1-14-200

1-14-200

1-7-100

1-7-100

1-7-50

1-7-50

0

1500

3000

4500

6000

0 0.5 1 1.5 2 2.5 3 3.5 4

Anodic current density (mA/cm2)

Po

we

r d

en

sity (

mW

/m2)

1-7-200

1-7-200

2-7-200

2-7-200

3.6-7-200

3.6-7-200

7-7-200

7-7-200

1-14-200

1-14-200

1-7-100

1-7-100

1-7-50

1-7-50

y = 0.9985x

R2 = 0.9981

0

2000

4000

6000

8000

0 2000 4000 6000 8000

Observed pow er density (mW/m2)

Calc

ula

ted pow

er

density

(mW

/m2)

y = 0.9997x

R2 = 0.9931

0.1

0.2

0.3

0.4

0.5

0.1 0.2 0.3 0.4 0.5

Observed voltage (V)

Calc

ula

ted v

olta

ge (

V)(A)

(B)

A anodic power density of

6840 mW/m2 (2.6 mA/cm2)

was achieved at an

anode/cathode area ratio of

14 and 200 mM phosphate

buffer

Source: Fan et al., Environ.Sci.Technol,(2008)

E = Eb – (ra / Sa + rc / Sc + ac / Cb) I

p = Eb i – (ra / Sa + rc / Sc + ac / Cb) i2

Eb ra rc re

V Ω cm2 Ω cm2 Ω cm2

0.500 32.3 284 285

E = Eb - (ra / Sa + rc / Sc + rm / Sm + a L / ( Sr * Ce)) I

27

Predict Internal Resistance of CEA MFC

Anode Cathode electrolyteCalculated

Rint

Measured

Rint

Power density

W/m3

ASR, (Ω cm2) 32.3 284 16.8 - -

50 mM buffer 2.3 20.3 9.6 32.2 34.4 697

100 mM buffer 2.3 20.3 4.8 27.4 26.9 1010

200 mM buffer 2.3 20.3 2.4 25.0 24.9 1120

7-7-200 (1.7 cm) 4.6 40.6 40.7 85.9 79.6 43

y = -0.0344x + 0.4865

y = -0.0269x + 0.5161

y = -0.0249x + 0.5228

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 5 10 15

current (mA)

vo

lta

ge

(V

) 50 mM

100 mM

200 mM

Linear (50 mM)

Linear (100 mM)

Linear (200 mM)

1. Remove membrane: Rm = 0

2. Double cathode: Rc = rc/Sc= 284 / 14 = 20.3 Ω

3. Double anode: Ra = ra/Sa= 32.3 / 14 = 2.3 Ω

4. Reduce electrode spacing:(17 mm to 1 mm)

re = 285/17 =16.8Ωcm2

5. Increase buffer concentrations

28

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30

Time (hour)

Pow

er

density (

W/m

3) 50Ω

1000Ω

50Ω

35Ω

20Ω

70Ω

100Ω

200Ω

500Ω

Continuous power generation in double CEA MFCs

A power density of 1010 W/m3

at 0.9mA/cm2


•acetate

• mixed culture

• phosphate

buffer

(pH =7)

29

Increasing pH buffer concentration reduces internal

resistance

0

200

400

600

800

1000

1200

0 0.2 0.4 0.6 0.8 1

Current denstiy (mA/cm2)

pow

er

density (

W/m

3)

50 mM

100 mM

200 mMy = -0.0344x + 0.4865

y = -0.0269x + 0.5161

y = -0.0249x + 0.5228

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 5 10 15

current (mA)

vo

lta

ge

(V

) 50 mM

100 mM

200 mM

Linear (50 mM)

Linear (100 mM)

Linear (200 mM)

30

Drawbacks of using phosphate buffer:

• Addition of high concentration of phosphate buffer is expensive

• Phosphate may cause eutrophication

Enhanced power generation using bicarbonate buffer

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70 80

Time (hour)

Pow

er

density

(W

/m3)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Volta

ge (

V)

pH 9.5pH 9pH 8 pH 8.5

10Ω

20Ω

25Ω

100Ω

15Ω

100Ω

30Ω

15Ω

20Ω

300Ω

35Ω

30Ω

7Ω

1000Ω

500Ω

15Ω

20Ω 20Ω

25Ω

1000Ω500Ω

25Ω

A power density of 1550 W/m3

(2770 mW/m2) at 1 mA/cm2 at

pH 9.0

Source: Fan et al., Environ. Sci. Technol, (2007)

0

400

800

1200

1600

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Current density (mA/cm2)

Pow

er

density

(W

/m3)

pH 7

pH 8

pH 8.5

pH 9

pH 9.5

0.00

0.20

0.40

0.60

0 0.5 1 1.5

Current density (mA/cm2)

Volta

ge (

V)

31

Proton transfer in MFCs

• Convection:

mechanical motion of the electrolyte

• Electric migration:

an electric field, i.e. an electrical potential gradient

• Diffusion:

a chemical potential gradient, i.e. a concentration gradient

Chemical fuel cells:• Strong acidic (H+) or alkaline (OH-) condition

• Very small electrode spacing, especially in

Membrane Electrode Assembly

Microbial fuel cells:

• Neutral pH: Low H+/OH- concentration

• Large electrode spacing

32

Proton transfer through electric migration

j

jjj

pp

pCz

Ct

tp: the transference number of proton, or the fraction of the total

current that proton carries;

Cp: the concentration of proton (M);

Cj: the concentration of ion j (M);

λp: the molar ionic conductivity for proton (Sm2mol-1);

λj: the molar ionic conductivity for ion j (Sm2mol-1);

zj :the charge on ion j

(Rieger 2001)

For an MFC with 0.1 M phosphate buffer solution (pH =7):

tp = 1.110-6

free proton transfer through electric migration is negligible33

Free proton transfer through diffusion

W = – DAΔC/δ

Fick’s Law:

W: the diffusion rate of protons through surface A (mol/s);

D: the diffusion coefficient of protons (m2/s);

δ: the membrane thickness (m);

A: cross-sectional area (m2);

∆C: the concentration difference (mol/m3).

At pH 7, ∆C

Proton transfer by proton carriers

e-

H2PO4-

(HCO3-)

e-

Bacteria

Anode

O2HPO42-(CO3

2-)

H2O

Cathode

CxHyOz

CO2

load

H+ H+

H2PO4- +H+ → HPO4

2-HPO4

2- +H+ → H2PO4-

Source: Fan et al., Environ. Sci. Technol, (2007)

35

Larger CEA-MFC

Ti wire (-)

Ti wire (+)

Ti wire (-)

Ti wire (+)

Inlets

Outlets

End plate

End plate

Cathode

Cloth

Anode

Anode

Cloth

Cathode

•Increase of surface area: 14 times

•Increase of volume: 12 times

Source: Fan et al., Energy Environ.Sci. 2012

Current density: 18 A/m2

Power density: 4.3 W/m2;

Specific internal resistance: ~20 mΩm2

36

Power density (W/m2) of small and scaled-up CEA MFCs

Phosphate buffer0.05 M 0.1 M 0.2 M

Small

(7 x 2 cm2)1.25 1.80 2.00

Scale-up

(100 x 2 cm2)

3.25 (3.7*) 4.12 4.32

Power densities were more than doubled in the scale-up MFC

* 150 mM acetate , HRT 3h

Power densities: 2.9 kw/m3, ~ 3times of anaerobic digester

Loading: over 90 kg COD/m3/d, 4 times faster than anaerobic digester37

Reasons for the good performance of CEA-MFC

CEA structure

Oxygen tolerant mixed culture

Thin, high-flux separator

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60

Time, h

Pow

er

density,

W/m

3

Air pump on Air pump off

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6

Time, d

Po

wer

den

sit

y, W

/m3

0

50

100

150

200

250

To

tal cu

rren

t, m

A

Power density

Total current

5015 Ω15 Ω

5 Ω

3 Ω

2 Ω

1.5 Ω

100 Ω

The biofilm can tolerate high level of oxygen Fast startup due to the oxygen tolerant biofilm


38

Performance of the CEA MFC in comparison with liter-scale air cathode MFCs

MFC type Anode material

Cathode material

Separator material

Volume(L)

Max. Power Density Max. power

CE Refer-ence

(W m-2) (W m-3) (mW) (%)

Double CEA Carbon clothCarbon cloth/Pt

None-woven Cloth

0.030 4.30* 2080# 62.3# 74-98This

study

Double CEA Carbon clothCarbon cloth/Pt

J-Cloth 0.0025 1.80 1010 2.5 - 12

Tubular Carbon veil Carbon cloth/Pt

CMI-7000 1 0.13 5.6 5.6 - 8

BipolarTi plate w/

MMO Ti plate w/

MMO Biopolar

membrane20 0.11 11 220 - 22

Biocathode Carbon felt Carbon felt CMI-7000 7.2 0.77 4.3 31 10-50 10

Double MEA

Carbon paperCarbon cloth/Pt

Nafion 1.5 0.16 3.5 5.3 5 11

Multiple electrode

GACCarbon cloth/Pt

NA 20 0.38 0.2 3.40.04-0.3

7

Biocathodegranular graphite

Carbon felt CMI7000 7.5 0.39 9.8 74 ~ 50 9


MFC Power density increase in Hong Liu’s lab

10 2 3 kW/m32005 2006 2007 2011

0.1 L1 mL 10 L 1 m3

2006 2011 2012 20152013 2017

2008-10

2015

2012-13

2010-15

2013-15

Reactor volume increase

IIP: 1448986 STTR Phase I: Next-Generation Microbial Fuel Cell for Highly Efficient Wastewater Treatment

CBET: 0955124 CAREER: Electromicrobiological Studies Using Microbial Electrochemical Systems Capable of Sustainable Energy Production and Waste Treatment

IIP: 1265144 I-Corps: Microibal Fuel Cells for Decentralized Wastewater Treatment and Energy Generation

CBET: 0828544 High Efficiency Bio-electrolytic Hydrogen Production from Biomass Using Nanostructure-Decorated Electrodes

IIP: 1312301 AIR Option 1: Technology Translation Sustainable Wastewater Treatment System for Food and Beverage Industry

Waste2Watergy40

IIP: 1660116 SBIR Phase II: Next-Generation Microbial Fuel Cell for Highly Efficient Wastewater Treatment2017

Phase I development

41

Widmer on-site testing

Pre

trea

tmen

t

tan

kMFC

Under ground

water pit

Pump1

Pump2

Nutrient

Flow chart of on-site testing at Widmer

EffluentNaOH

Waste2Watergy 42


Power and voltage generation during Widmer on-site testing

0

1

2

3

4

5

6

7

8

9

0

200

400

600

800

1000

1200

2/17 2/27 3/9 3/19 3/29 4/8 4/18 4/28 5/8 5/18 5/28

volt

age,

V

Po

wer

den

sity

, mW

/m2

Date

power density voltage

43


Daily COD data and removal rate (% pretreatment effluent) during Widmer on-site testing

Waste2Watergy 44

Widmer on-site testing conclusions

The wastewater from Widmer can be used to produce electricity using our CEA-MFC. The produced power density can reached up to 1000 mW/m2.

The recovery of MFC from incidents, such as water stoppage (a few hours) was fast, normally in minutes. The recovery from extremely high pH (> 12.5) took about 1-2 weeks.

Wastewater COD can be removed effectively, up to over 70% at an HRT of 4 hours. It is expected that the COD removal can be further improved with further optimization and longer HRT.

An over 80% reduction in surcharge (based on BOD and TSS) is expected for Widmer if our technology is successfully implemented based on current results.

45

Meduri Farms on-site testing

Waste2Watergy

Under ground

water pit

Pre

trea

tmen

t

tan

kMFC

Nutrient

(N,P,

Vitamins)

Flow chart of on-site testing at Meduri Farms

EffluentCa(OH)2

Heating

tank

Overflow

Backup Pump

1

2

3

4 5

46


Power and voltage generation

Waste2Watergy 47


Daily COD data and removal rates Daily TSS data and removal rates

Comparison of influent (left) and effluent (right) 48

Meduri Farms on-site testing conclusions

The produced power density can reach up to 900 mW/m2, which is about the same level as we tested at Widmer.

The re-startup of MFC reactors was very quick. The reactor can be fully started up in about a week. The recovery of MFC from incidents, such as water stoppage (a few hours) was fast.

Wastewater COD can be removed effectively, up to over 80% at an HRT of 4 hours. The total COD removal is about 90%.

The total TSS removal is over 90% during the test period, with an average of 97%.

An over 80% reduction in surcharge (based on BOD and TSS) is expected for Meduri Farms if our technology is successfully implemented based on current results.

Waste2Watergy 49

Phase II development

Further scale-up: from cubic meter to 20-ft shipping container

Enhanced pretreatment (anaerobic process, methane generation)

Added anaerobic membrane bio-reactor for better effluent quality and possible water reuse

Investigating the possibility of energy neutral/positive

50

Containerized MFC system

51Waste2Watergy

Is energy neutral/positive possible?

MFC vs AD vs ASCapital

costs

($/kg COD)

O/M cost

($/kg COD)

Product

revenue

($/kg COD)

Offset

(product revenue -

cost) ($/kg COD)

AS 0.1 0.3* 0 -0.4

AD 0.01

Advantages of MFC over Anaerobic Digestion

1) Faster wastewater treatment.

2) Faster start-up and more stable operation.

3) MFCs can produce better effluent quality.

4) Electricity can be generated directly in MFCs without the need to

produce biogas first.

5) MFCs are suitable for small- to medium-scale decentralized

wastewater treatment when AD cannot be utilized.

6) The performance of MFC modules can be easily monitored.

Waste2Watergy

High Strength

Wastewater

Scaled to Fit: Concentration and Flow Cleaner water &

electricity

Equalization tank MFC modules

53

Acknowledgements

54

http://www.defense.gov/

Questions

?

Email: [email protected]

55
mailto:[email protected]

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