List of figures
Fig. 1. Waste water treatment plant configuration and reconciled operational data.
Fig. 2. Distributed and micro CHP systems’ life cycle phases and processing steps for
comparative LCA.
Fig. 3. Primary impact characterisations: comparison between individual processes in the
biogas to grid system on the basis of 11340 MJ biogas production. CFC: Chlorofluorocarbon;
DCB: 1,4 Dichlorobenzene. Both embedded and operational impacts are included.
Fig. 4. GWP, AP and POCP: comparison between individual processes in the PEMFC cradle
to grave micro-generation system on the basis of 11340 MJ biogas processing. The x-axis
shows the processing steps, thus the hotspot in each category.
Fig. 5. Summary of environmental performance comparison results of sewage sludge
products.
Fig. 6. Monte Carlo simulation framework integrated with LCA.
Fig. 7. Probability distributions of the two most and two least sensitive impact potentials with
respect to their standard deviations from their mean values.
Fig. 8. Relative placements of the various biogas based cradle to grave CHP systems, in
terms of cost per unit energy output vs. avoided emissions compared to equivalent natural gas
based systems.
Waste water
Primary sludge t d-1
Fixed C
4.2
Volatile C 18.3
H
3.3
O
15.0
N
3.6
S
0.6
Ash
15.0
Activated
sludge
aeration
Primary settler
Primary
sludge
Biogas constituents t d-1
CH4 11.21
Gas grid
CO2 10.9
CHP
Digested matter t d-1
C2.25H5.39N0.24Cl0.002O 46.44
Sulphur recovered
0.64
Ash
23.8
Metals
48.96 kg d-1
Metal
Cadmium (Cd)
Zinc (Zn)
Vanadium (V)
Lead (Pb)
Copper (Cu)
Chromium (Cr)
Nickel (Ni)
Cobalt (Co)
Thallium (Tl)
Arsenic (As)
Mercury (Hg)
Boron (B)
Molybdenum (Mo)
Biogas
Activated
sludge
Clean-up,
Storage
Distributed, micro generations
Agricultural application
Ash content
Silicon oxide (SiO2)
Aluminium oxide (Al2O3)
Iron oxide (Fe2O3)
Titanium oxide (TiO2)
Manganese oxide (Mn3O4)
Calcium oxide (CaO)
Magnesium oxide (MgO)
Sodium oxide (Na2O)
Potassium oxide (K2O)
Phosphorus pentoxide (P2O5)
Secondary Water to river
settler
or reserve
Activated sludge t d-1
Fixed C
4.8
Volatile C 11.6
H
2.2
O
9.2
N
3.2
S
0.04
Cl
0.16
Ash
8.8
Anaerobic
digestion
System boundary
for LCA
Digested
matter
Weight %
14-34
6-23
5-9
1-2
0.1
10-20
2-6
0.5-1.5
1-7
15-40
Mass mg kg-1 sludge
0.6
220
7. 5
47
166
13
14
1.9
0.05
0.10
0.4
14
5
Molar mass
60.08
102
159.7
79.9
228.8
56
40
62
94
283.9
Molar mass
112
65
51
207
63.5
52
58.7
58.9
204
74.9
200.6
10.8
96
Density g cm-3
2.65
3.95
5.24
4.23
4.86
3.35
3.58
2.27
2.35
2.39
Molar volume cm3 mol-1
13
9.16
8.34
18.3
7.12
7.28
6.59
6.62
17.2
13.1
14.8
4.39
9.33
Fig. 1. Waste water treatment plant configuration and reconciled operational data.
Life cycle phases
Material of construction
Biogas from storage Electrical energy
generation
Material of construction
Exhaust gas to
Hot exhaust gas Heat recovery steam atmosphere
generator
Decommissioning
Decommissioning
Reuse, recycle
Reuse, recycle
Processing steps
Fig. 2. Distributed and micro CHP systems’ life cycle phases and processing steps for
comparative LCA.
AD plant
construction
0.23%
GWP -836.17 kg CO2 equivalent
Digested
matter
application in
agriculture
-31.57%
Biogas
production
-68.67%
AP 0.076 kg SO2 equivalent
Biogas
production
0%
AD plant
construction
6.58%
Digested
matter
application in
agriculture
93.42%
EP 2.479 kg Phosphate equivalent
Biogas
production
0%
AD plant
construction
0.081%
Digested
matter
application in
agriculture
99.919%
ODP 1.047 × 10-7 kg CFC equivalent
Biogas
production
0%
Digested
matter
application in
agriculture
0%
AD plant
construction
100%
FAETP 23.609 kg DCB equivalent
AD plant
construction
2.8%
Biogas
production
0%
Digested matter
application in
agriculture
97.2%
HTP 136.367 kg DCB equivalent
Biogas
production
0%
AD plant
construction
1.53%
Digested
matter
application in
agriculture
98.47%
MAETP 20870 kg DCB equivalent
AD plant
construction
4.95%
Biogas
production
0%
Digested
matter
application in
agriculture
95.05%
POCP 7.214 × 10-3 kg ethylene
equivalent
AD plant
construction
11.812%
Biogas
production
88.188%
Digested
matter
application in
agriculture
0%
TETP 34.578 kg DCB equivalent
AD plant
construction
0.211%
Biogas
production
0%
Digested
matter
application
in
agriculture
99.789%
Fig. 3. Primary impact characterisations: comparison between individual processes in the
biogas to grid system on the basis of 11340 MJ biogas production. CFC: Chlorofluorocarbon;
DCB: 1,4 Dichlorobenzene. Both embedded and operational impacts are included.
GWP in kg CO2 equivalent
700
500
300
100
-100
-300
-500
-700
-900
AP in kg SO2 equivalent
PEMFC cradle to grave system
Digested
matter
application to
agriculture
Biogas
production
Biogas
combustion
in PEMFC
Total
1.96
-263.95
-574.18
634.18
-836.17
AD plant
infrastructure
Digested
matter
application to
agriculture
Biogas
production
Biogas
combustion
in PEMFC
Total
0.005
0.071
0
0.015
0.015
AD plant
infrastructure
Digested
matter
application to
agriculture
Biogas
production
Biogas
combustion
in PEMFC
Total
0.000852
0
0.006361
0.002743
0.015
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
PEMFC cradle to grave system
POCP in kg ethylene equivalent
AD plant
infrastructure
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
PEMFC cradle to grave system
Fig. 4. GWP, AP and POCP: comparison between individual processes in the PEMFC cradle
to grave micro-generation system on the basis of 11340 MJ biogas production and
processing. The x-axis shows the processing steps, thus the hotspot in each category.
Sewage
sludge
Digested
matter (DM)
for agricultural
application
Carbon sink
Carbon source
Anaerobic
digestion
Storage
Biogas
Avoided emissions by
Cradle to grave system
GWP, kg CO2Eq.
AP, kg SO2Eq.
POCP, kg
Ethylene-Eq.
Biogas grid, per MJ
0.0793
4.47×10-5
6.59×10-6
Biogas – PEMFC, per MJ
0.1200
7.57×10-5
1.11×10-5
Biogas – SOFC, per MJ
0.0951
5.18×10-5
7.65×10-6
Biogas – SOFC-GT, per MJ
0.0916
4.59×10-5
7.20×10-6
Biogas – Micro GT, per MJ
0.0982
4.26×10-5
7.64×10-6
0.44-0.77
0.01186
0.00093
DM, per kg
1. Gas grid
2. Proton exchange membrane
fuel cell (PEMFC) – Micro
CHP generation
3. Solid oxide fuel cell (SOFC) –
Distributed CHP generation
4. SOFC-Gas Turbine (GT) –
Distributed CHP generation
5. Micro-GT – Distributed CHP
generation
Fig. 5. Summary of environmental performance comparison results of sewage sludge
products.
Determination of uncertain and
independent variables for Monte
Carlo simulation
Determination of a standard deviation and a
probability distribution function for each
uncertain and independent variable
Selection of values of the uncertain and independent variables
using an Monte Carlo algorithm
No
Calculation of relevant primary impact characterisations and %
reduction from the basis impact characterisations
Completed number
of simulation runs?
Yes
Calculation of chances of each % reduction
from the basis impact characterisations
End
Fig. 6. Monte Carlo simulation framework integrated with LCA.
No
Yes
Change the
standard
deviation and
probability
distribution
function ?
100%
90%
GWP kg CO2 equivalent
POCP kg ethene equivalent
80%
Probability distribution %
MAETP kg DCB equivalent
70%
EP kg phosphate equivalent
60%
50%
40%
30%
20%
10%
0%
(25-19)%
(19-14)%
(14-8)%
(8-3)%
(3-(-3))%
((-3)-(-8))% ((-8)-(-14))% ((-14)-(-19))% ((-19)-(-25))%
Standard deviation from mean value
Fig. 7. Probability distributions of the two most and two least sensitive impact potentials with
respect to their standard deviations from their mean values.
Cost per unit energy production on 0-1 scale
1
SOFC
0.9
PEMFC
0.8
0.7
0.6
SOFC-GT
0.5
0.4
Micro GT
0.3
0.2
0.1
0
Biogas to 0
grid
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Avoided environmental impact potential on 0-1 scale
Fig. 8. Relative placements of the various biogas based cradle to grave CHP systems, in
terms of cost per unit energy output vs. avoided emissions compared to equivalent natural gas
based systems.