lca and risk assessment of sewage sludge application to ...... 1 1 lca and risk assessment of sewage...
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LCA and risk assessment of sewage sludge application to land compared to phosphorus
recycling technologies
Fabian Kraus, Kompetenzzentrum Wasser Berlin gGmbH
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Scope, System boundaries (simplified)
System boundaries
Emissions to air
Emissions to water
Waste and emissions to soil
Sludge treatment incl.
digestion
Chemicals Energy
(Electricity & Heat)
Fossil fuels Transportation Materials, Infrastructure
Sludge treatment incl.
digestion
Sludge Agricultural application
Sludge
+ struvite recovery
Co- incineration in
power plant Agricultural application
Sludge treatment incl.
digestion
Sludge Mono- incineration
recovery of technical H3PO4 for
DAP production
Agricultural application
Sludge treatment incl.
digestion
Sludge Mono- Incineration
recovery of technical H3PO4 for
DAP production
Agricultural application + N2O
mitigation
Disposal of slag/ residual ash
Value of recovered fertilizer equivalent
(recovery rate)
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Non-renewable cumulative energy demand (CED) coal, oil, natural gas, uranium
Take home messages: #1 anaerobic digestion highly advantageous #2 turn-off between energy recovery via power plant and P recovery
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Global warming potential (GWP Fossil CO2, CH4, N2O
Take home messages: #1 indirect emissions (energy recovery) determining overall footprint #2 direct emissions (N2O) relevant! – reduction of point sources reasonable
Diffuse source of N2O
Point source of N2O
Reduction possible
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Human toxicity potential (HTP) heavy metals in agricultural soils
Take home messages: #1 Struvite and technical P-acid are products with negligible contaminant-level #2 (Sludge and) sludge ash contains high HM-loads, HM removal recommended
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Summary
Sludge valorization in agriculture is from the overall energy perspective advanced compared to mono-incineration (and P recovery from ash) due to partly substituted nitrogen and lower energetic efforts. However high metal loads and other potential hazardous substances are also put to arable land.
A combination of struvite recovery in EBPR in combination with energetic valorization of sludge in a power plant reveals environmental benefits in terms of Energy recovery and GWP, it is accompanied by operational benefits (e.g. reduced sludge volume due to improved dewatering) and high electric efficiency in the power plant
P recovery from ash after mono-incineration can reduce the GWP compared to agricultural sludge valorization if N2O mitigation measures are put in place and it can reduce the input of hazardous substances if a recovery process is chosen, that significantly reduces metal contamination compared to sludge ash
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Environmental risk definition
𝑹𝑹𝑹𝑹 =𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷
RQ: Risk quotient PEC: Predicted environmental concentration PNEC: Predicted no-effect concentration TGD: Technical Guidance Document on Risk Assessment
Expected future exposure through exposure models (current
contamination also verified by measurements)
Environmental compartment
Inpu
t O
utpu
t
Input variables
1
• Ecotoxicity • Human toxicity
Toxicity tests
• Expression of knowledge • Depending on the type of tests and the
number of trophy levels tested
Assessment factor
• Soil organisms: • Ecotoxicity tests for soil organisms • Derived from toxicity test for water
organisms • Groundwater (and pore water):
• Ecotoxicity tests for water organisms • Minor threshold values for groundwater • Tolerable daily intake (humans)
• Humans • Tolerable daily intake
PNEC per endpoint
Exposure model (TGD)
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Exposure model Atmospheric deposition and fertilizer application Fertilizer amount Pollutant concentration
Volatisation Henry-constant
(KH)
Plant uptake Bio-concentration-
factor (BCF)
Precipitation
Leaching Sorption coefficient (Kd) Infiltration rate
Biodegredation Biological half-life
(DT50)
Initial concentration (c0)
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Risk quotient
Shar
e of
exc
eedi
ng th
e ris
k qu
otie
nt [%
]
0,001 0,01 0,1 1 10
0
20
40
60
80
100
Unacceptable risk Acceptable risk Negligible risk
Unlikely
About as likely as not
Likely
Very likely
Very unlikely
prob
abili
ty
(acc
ordi
ng to
IPCC
, 201
0)
expected damage
Results of probabilistic risk assessment
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Ars
enic
Lea
d
Cad
miu
m
Chr
omiu
m
Cop
per
Nic
kel
Mer
cury
Ura
nium
Zin
c
PAH
Ben
zo(a
)pyr
en
PCD
D/F
+ dl
-PCB
Hum
an h
ealth
Results of probabilistic risk assessment So
il or
gani
sms
Gro
undw
ater
=
pore
wat
er!
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Zinc and endpoint soil organisms Si
mul
atio
n re
sults
[%]
Refe
renc
e
Stru
vite
from
slud
ge
Stru
vite
from
cen
trat
e
Slud
ge a
nd sl
udge
ash
AshD
ec
Rene
wab
le o
r con
vent
ioal
fe
rtili
zer
(tech
nica
l P-a
cid)
Phos
phat
e ro
ck
Conv
entio
nal f
ertil
izer
0
20
40
60
80
100
mg Zn/kg P2O5 n
Conventional fertilizer 1 409 ± 2 893 104
Phosphate rock 807 ± 560 31
Renew. or conv. fertilizer (technical P-acid) 4,5 ± 1,5 3
AshDec 12 195 ± 3 545 150 (calc)
Sludge and sludge ash 13 402 ± 3 882 150
Struvite from centrate 124 ± 160 10
Struvite from sludge 264 ± 145 8
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17α
- Eth
inyl
estr
adio
l
17β
-Est
radi
ol
Bez
afib
rat
Car
bam
azep
ine
Cef
urox
ime
Cip
roflo
xaci
n
Cla
rithr
omyc
in
Dic
lofe
nac
Lev
oflo
xaci
n
Met
opro
lol
Sul
fam
etho
xazo
le
Soi
l org
anis
ms
Results of probabilistic risk assessment G
roun
dwat
er
= po
re w
ater
!
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Sim
ulat
ion
resu
lts [%
]
Refe
renc
e
Slud
ge
0
20
40
60
80
100
17β-Estradiol and endpoint groundwater
0.0e
+00
1.0e
-05
2.0e
-05
Jahre
PE
C B
oden
[mg/
kg]
0 1 2 3 4 5 6 7 8 9 10
PEC
soil
[mg/
kg]
years
DT50 = 1-10 d
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Summary
Under the background of made assumptions… An exceeding of the TDI (endpoint human health) is not expected
(cadmium is priority hazard) An exceeding of the PNEC for soil organisms could not be
excluded for zinc, whereby sludge and sludge ash significantly increase the risk quotient
Groundwater is the most sensitive endpoint: – an exceeding of the PNEC could not be excluded for several heavy metals – this accounts especially for cadmium (sedimentary phosphate rock and
conventional fertilizers produced from sedimentary rock) and copper and zinc (sludge and sludge ash)
Struvite and fertilizers derived from technical phosphoric acid do not increase risks for any included substance in the assessment
An actual exceeding of any PNEC is unlikely for organic substances (incl. pharmaceutical residues) also for sludge
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Recommendation
What should Europe do? Traditional sludge valorization in agriculture? Struvite recovery prior sludge disposal? Recovery from ash after mono-incineration?
It depends on the local boundary conditions! Agglomeration areas (> 1-3 Mio pe): reasonable economy of scale
for mono-incinerators and P recovery plants from ash
Rural areas: either long sludge transportation routes to have a reasonable economy of scale or other solutions than mono-incineration, e.g. struvite recovery and/or traditional sludge valorization (incl. quality control)