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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
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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.
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Phosphate loss The biggest problem you never heard of
K. Syers, et al., Phosphorous And Food Production, UNEP Year Book 2011.
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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 !
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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
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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
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Digested sewage sludge contains tons of
phosphate
8-9% Phosphate
Toxic metals prevent direct use
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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.
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Microbial fuel cells, a source of: power, protons and
electrons
Biological systems stock hydrogen!
power + H+ + e-
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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
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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.
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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.
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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
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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.
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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.
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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.
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Remobilisation set-up
Stirring
motor Anode in
bioreactor
Cathode
Remobilisation
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Sewage sludge pretreatment
Non treated digested
sewage sludge provides
insufficient surface area
for a productive
phosphate extraction
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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
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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
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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
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-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
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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
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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
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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.
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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
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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
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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
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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
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Thank you for your attention
Acknowledgements
Christèle Bastian
Manuel Happe
Daniel Zufferey
Eric Mabillard
Nicolas Schmidt
Amandus Steiner