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Institut Technologies du vivant Institut Technologies du vivant

Microbial fuel cell enables

phosphate recovery from

digested sewage sludge as

fertilizer

Innovation Day

When Biotech becomes Cleantech

November 10, 2011

Presented by Fabian Fischer

HES-SO Valais Life Technologies Institute

Institut Technologies du vivant

Phosphor is an essential element

Corn with and

without phosphor

fertilizer in Brazil’s

Cerrado region

K. Syers, et al., Phosphorous And Food Production, UNEP Year Book 2011.


Phosphate loss The biggest problem you never heard of

K. Syers, et al., Phosphorous And Food Production, UNEP Year Book 2011.


Life-time of phosphor reserves

D. Cordell, et al., Global Environmental Change, 2009, 19, 292–305.

A reduced

availability of

phosphate will

reduce the

world’s

population

Phosphate

has to be

recycled !


What are the accessible renewable sources?

Urban waste waters

Sewage sludge and garbage incineration ash

Bone and meat waste

Biowaste from biorefineries

Sea and river sediments


Sewage sludge is rich in phosphate

P

Fe

Ca

ICP-OES Analysis indicates also As, Cd, Cr, Cu, Pb and

others in trace elements.

Because: FeCl3 + PO43- FePO4 +3Cl-

K In

Mg

S

http://www.icp-oes.net/images/torche2.jpg


Digested sewage sludge contains tons of

phosphate

8-9% Phosphate

Toxic metals prevent direct use


What are the technical options?

Acidic treatment of sewage sludge ash

90% recovery but contaminated

Basic treatment of sewage sludge ash

30% recovery, not contaminated

Plasma separation appears not economic but pure

phosphate is recovered

Up to date no method is economically

successful

L. Hermann, Rückgewinnung von Phosphor aus der Abwassereinigung, Eine Bestandesaufnahme, BAFU 2009.


Microbial fuel cells, a source of: power, protons and

electrons

Biological systems stock hydrogen!

power + H+ + e-


The fuel cell and the microbial version

Nafion membrane

H+

x Bio-Hn 2H+ + 2e-

H2 2H+ + 2e-

2H+ + 2e- + O H2O

anode cathode

V+ _

e- e-

Microbial fuel cell

Chemical fuel cell


Coulombic efficiency of a microbial fuel cell

O6H6CO24e24H6OOHC

O12H24e24H6O

24e24H6COO6HOHC

2226126

22

226126

K. Rabaey et al., Biotechnology Letters 2003, 25, 1531-1535.

When microbes starve and only glucose is provided a

columbic efficiency of 89% was achieved.


Electron harvest and products of microbial fuel cells

Anode harvests electrons:

a) bio-film

b) collision

c) pilli

d) mediator

Cathode produces:

electricity

hydrogen

F. Fischer, Bulletin SEV/VSE electrosuisse 2011, 11, 26-29.


ca

tho

de

an

od

e

ca

tho

de

an

od

e

ca

tho

de

an

od

e

H+ H+ H+

V

R

n

Microbial fuel cell stacks for higher power


Power characteristics of microbial fuel cells

Current [mA] P

ow

er

[mW

]

Po

ten

tia

l [V

]

Power

characteristics

of a serial

microbial fuel

cell stack

F. Fischer, Bulletin SEV/VSE , electrosuisse, 2011, 11, 26-29.


A

PO43- Fe3+

Fen+

H+

Anode e- e- Cathode

+ H3PO4

Fe3+ PO43-

Fen+ + H3PO4

e-

e-

e-

e-

e-

e-

e-

Microbial fuel cell enables phosphor bio-refining

Microbial fuel cell

Fertilizer

Sew

ag

e s

lud

ge

Phosphate

Waste

wate

r

F. Fischer et al., Bioresource Technology, 2011, 102, 5824–5830.


Waste water Purified

water

Cleantech through the integration of microbial fuel

cell power and phosphate recycling

Microbial fuel cell

treatment

(New art)

Electric

power

Phosphate

refining

Sludge

F. Fischer, Bulletin SEV/VSE, electrosuisse 2011, 11, 26-29.


Remobilisation set-up

Stirring

motor Anode in

bioreactor

Cathode

Remobilisation


Sewage sludge pretreatment

Non treated digested

sewage sludge provides

insufficient surface area

for a productive

phosphate extraction


Sewage sludge needs to be grinded

Grinded sewage sludge

yields higher than

untreated

Milling with a 120 mm cut-

off size

Smaller particle formation

is impractical due to

overheating


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 4 6 8

[V]

[Days]

Standing and working potential with an E.coli

cultivation


0.1

0.2

0.3

0.4

0.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

Cu

rren

t [m

A]

Time [days]

Current flow into the sewage sludge cathode


-0.0005

0.0005

0.0015

0.0025

0.0035

0.00

0.05

0.10

0.15

0.20

0.25

0.00 0.02 0.04 0.06

Po

wer

den

sit

y [

mW

/cm

3]

Wo

rkin

g a

no

de p

ote

nti

al

[V]

Current density [mA/cm3]

Rint=2.6 kΩ

Power current plot and polarization curve


Remobilisation results

Entry Sludge

(FePO4)

[g (mg)]

Time

[d]

Particles

[mm]

Yield

H3PO4

[g/L]

Yield

H3PO4

[%]

1 1.7 (240) 7 ~106 0.003 0.02

2 1.7 (240) 7 50 0.104 2.9

3 3.3 (470) 7 50 0.308 4.4

4 1.7 (240) 6 50 0.337 9.2

5 1.9 (270) 19 50 0.594 14.6

6 0.4 (60) 9 50 0.213 22.5

7 0.2 (30) 14 50 0.201 43.4

8 0.3 (40) 21 50 0.404 68.2

9 0.2 (30) 21 50 0.372 82.3


How does the reduction work?

24

3 Fe(III)PO4 + 3e-/3H+ Fe3(II)(PO4)2 + H3PO4

A hypothetically formed intermediate is Vivianite.

Fe3(II)(PO4)2 + ne- + nH+ H2PO4

- + Fen+

8000

12000

16000

20000

24000

10 20 30 40 50

Inte

ns

ity [

Co

un

ts]

2 q [°]

The reduction

reaction is not

proven because

FePO4 is integrated

in amorphous

sewage sludge

Ca2O3

SiO2

Powder X-ray of sewage sludge


How does the reduction work?

Fe/P ratio Reference

FePO4

Grain

% weight 2.03 2.48

% atom 1.13 1.37

Model system with pure FePO4 shows that iron accumulates in

remaining sludge particles.


Basic recovery principle with a microbial fuel cell

Fe(III)PO4 + 3e-/~3H+ H2PO4-

Pure ortho-phosphate is recovered

from sewage sludge as shown by

phosphorous 31P-NMR.

Sludge Microbial

fuel cell


Tox free fertilizer, struvite

% weight Match [%]

% weight Element Sample Reference

N 6.05 6.16 98

O 60.28 63.09 96

Mg 12.10 14.07 86

P 14.82 16.068 92

Na 2.5

Si 0.8

Cu 0.17

Cl 1.02

K 0.8

Fe 0.11

Ca 0.08

Elemental analysis of

struvite (RDX)

No

n to

xic

imp

uritie

s

Struvite

H2PO4

- + Mg2+ + NH4

+ NH4MgPO4


Green recovery fits in

Raw phosphate

Superphosphate 18-20% P2O5

Triple superphosphate 40-48% P2O5

Ammonium phosphate 46-48 P2O5

Obtained struvite ~ 33% P2O5

Mining

Microbial fuel cell


Conclusions

A cleantech concept:

The integration of power generation by microbial fuel cell

technology and phosphate recovery is possible

Produced phosphate fertilizer is non toxic

Phosphate demands and prices will rise

Decentralized sustainable phosphate production


Thank you for your attention

Acknowledgements

Christèle Bastian

Manuel Happe

Daniel Zufferey

Eric Mabillard

Nicolas Schmidt

Amandus Steiner

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