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Waste Management Services
Calculating the Carbon Footprint
of Various Municipal
Waste Management Practices
Allan Yee, CD, M.Sc., P.Eng.
Senior Engineer Organics Processing
5 February 2013
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Outline Municipal Waste Management Decision Making IAW the 4 Rs
Waste Management Carbon Emission Effects
Carbon Footprint of Landfill Disposal
Waste Recovery Example: LFG Capture
Waste Recycling/Reuse Example: Composting
Residential Recycling Discussion
Waste Reduction Example: Grasscycling
Summary and Conclusions
Waste Management Hierarchy: the 4 Rs
Reduce
Reuse
Recycle
Recover
Hig
her
Pre
fere
nce
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Carbon Emission Effects of Waste
Management Practices Every activity/process has a carbon footprint that can
be measured and/or calculated.
The carbon footprint (GHG emissions) of waste
management activities comes from:
Activity/process energy inputs;
Degradation of organic materials during activity;
Production of energy/energy containing substances.
Comparison of carbon footprints of alternative waste
practices.
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Landfill Gas Generation
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Landfill Gas Emissions Disposal and degradation of organic materials in a landfill under anaerobic conditions will generate GHGs.
CH4 is main GHG of concern as CO2 is biogenic.
Landfill emissions are the biggest contributor to the carbon footprint of most municipal waste management systems. Emissions from upstream extraction and consumption of fossil fuels in collecting waste plus energy inputs into landfilling efforts are relatively minor in comparison.
6% of total CH4 emissions worldwide are attributed to landfills.
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Methane Generation Potential, Lo
Lo = amount of CH4 that can theoretically be produced from landfilling one tonne of waste
Lo = MCF x DOC x DOCf x F x (16/12) x 1000 kgs
CH4/tonne waste
Where Lo = CH4 generation potential, kgs/tonne of waste
MCF = CH4 correction factor, fraction
DOC = degradable organic carbon, t C/t of waste
DOCf = fraction of DOC that dissimilates under landfill conditions
F = fraction of CH4 in landfill gas
16/12 = stoichiometric factor for conversion of CH4 to carbon
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Time Distribution of Lo
Mass of material landfilled M, times Lo yields the maximum amount of methane that can be generated from that material.
Applying a first order decay function (e-kt) to M x Lo will give a time distribution to the emissions.
Resulting relationship commonly known as Scholl Canyon Model.
Summation of Individual FOD Curves Over Time
CH4
Emissions
(Q)
Time (Yrs) ∞ 0 1 2
Time period of
active landfilling
100
Individual first order decay
(FOD) time distribution
curve for methane
generation
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Numerical Approximation of FOD
Model Equation
Qt = ∑ 2k Lo Mi e-kti
i=1
n
Where Qt = total LFG emission rate, volume/time
n = total time periods of waste placement
k = methane generation rate constant, time-1
Lo = methane generation potential, volume/mass of waste
ti = age of the ith section of waste, time
Mi = mass of wet waste, placed at time i
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Waste Recovery Example:
Landfill Gas Collection
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Landfill Gas Collection Systems
Network of interconnected gas extraction wells installed in capped portions of landfill site.
Suction blowers capture and transport LFG from wells to a central point where gas is processed for straight combustion (flaring) or energy recovery (power, CHP, CNG, etc.).
Typical 75% capture efficiency for collection systems: comparisons of CH4 captured vs. generated.
Further 10% oxidation of CH4 emissions through the cover system of a landfill.
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Edmonton’s LFG Capture System
In operation at Clover Bar Landfill since 1992,
current LFG flow is about 65,000 standard m3/day,
with average CH4 content of 52%.
2011 data:
City Scholl Canyon model calculated 8,122 tonnes CH4
generated.
Capital Power recorded 6,384 tonnes CH4 captured.
Net emissions difference, counting flaring/power
generation and cover oxidation = 32,848 tonnes CO2-e.*
*Using a GWP of 21 for CH4
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Waste Recycling/Reuse Example:
Composting
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Carbon Footprint of Composting Carbon footprint = emissions from:
Process of composting [mass of material composted x
composting emission factors];
Upstream extraction and consumption of the energy inputs into
the operation [quantities of fuel used x respective emission
factors]; and
Landfilling of residuals from process [mass of residuals x Lo].
Differences between above and emissions from a
baseline [landfilling of materials composted] are the
emission reductions [offsets] from the operation.
Basic Composting System Boundary, Inputs
and Outputs
Fuel (Diesel)
Waste collection,
sorting,
transportation
Sorting
Aerobic Conversion
Compost
End User
On site use of
electricity
On site use by
equipment
Electricity from grid
Landfill)
Recycle
Waste Production
(households,
commercial)
System Boundary Limit
Adapted from CDM (2005)
Windrow Composting
Baseline Emissions Ebaseline = [Mdelivered x (MCF)(DOC)(DOCF)(F)(16/12) –R][1-OX][GWPmethane]
Where Ebaseline = CH4 emissions from landfilled waste in CO2 equivalent (tonnes)
Mdelivered = waste delivered to composting facility (tonnes)
MCF = methane correction factor
= 1 for managed landfills (IPCC default)
DOC = degradable organic fraction of waste (tonne C/tonne waste)
= 0.19 for Alberta (calculated using Environment Canada data)
DOCF = fraction of degradable organic carbon dissimilated
= 0.77 (IPCC default)
F = fraction of LFG that is CH4, assumed to be 0.5
16/12 = stoichiometric factor (molecular weight fraction of CH4/C)
R = recovered landfill gas at baseline landfill (measured)
OX = landfill oxidation factor
= 0.1 for landfills with soil or compost covers (IPCC default)
GWPmethane = global warming potential of methane of 25 (IPCC default)
Diesel Usage Emissions Ediesel = (FCO2)(Vdiesel) + (FCH4)(Vdiesel)(GWPCH4) + (FN2O)(Vdiesel)(GWPN2O)
Where Ediesel = direct GHG emissions from diesel combusion, kg CO2-e
FCO2 = emission factor for CO2 emissions from diesel combustion
= 2.730 kg CO2 per m3 (CAPP value)
Vdiesel = volume of diesel gas consumed (m3)
FCH4 = emission factor for CH4 emissions from diesel combustion
= 0.000133 kg CH4 per m3 (CAPP value)
GWPCH4 = global warming potential for CH4 of 21 (IPCC default)
FN2O = emission factor for N2O emissions from diesel combustion
= 0.0004 kg N2O per m3 (CAPP value)
GWPN2O = global warming potential for N2O of 310 (IPCC default)
Diesel Production Emissions Ediesel,p = (FCO2,p)(Vdiesel) + (FCH4,p)(Vdiesel)(GWPCH4) + (FN2O,p)(Vdiesel)(GWPN2O)
Where Ediesel,p = upstream GHG emissions from diesel production, kg CO2-e
FCO2,p = emission factor for CO2 emissions from diesel combustion
= 0.138 kg CO2 per m3 (CAPP value)
Vdiesel = volume of diesel gas consumed (m3)
FCH4 = emission factor for CH4 emissions from diesel production
= 0.0109 kg CH4 per m3 (CAPP value)
GWPCH4 = global warming potential for CH4 of 21 (IPCC default)
FN2O = emission factor for N2O emissions from diesel production
= 0.000004 kg N2O per m3 (CAPP value)
GWPN2O = global warming potential for N2O of 310 (IPCC default)
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ECF Example
Edmonton Composting Facility System
Boundary, Inputs and Outputs Collected
Mixed
Residential
MSW
Pre-processing
(sorting)
ECF –
mechanical
plant
Residues to
landfill w/ no
LFG
Collection
Compost curing
Collected waste
wood
On-site waste
wood chipping
Dewatered
municipal
biosolids
Biosolids/wood
chip composting
Screening cured
compost
Residues to
landfill w/ LFG
collection
Biosolids/wood
chip mixing
On-site power
use
On-site natural
gas use
On-site diesel
use
On-site
gasoline use
On-site
propane use
Electricity from
grid
Natural gas
Diesel fuel
Gasoline
Propane
Compost sales
to end users System Boundary
10,000 tonnes
110,000 tonnes
Primary Residuals 14,000 tonnes, 13.4%organic
Secondary Residuals 15,000 tonnes, 45.3%organic
14,000,000 kWh
29,600 GJ
483,900 L
1,280 L
1,740 m3
Tertiary Residuals 2,000 tonnes, 45.3%organic
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Calculation of Emissions and Offsets
for the ECF*
Baseline emissions from landfilling feedstock = 263,340 tonnes CO2-e.
Project Emissions of 50,123 tonnes CO2-e:
Composting = 12,900 tonnes CO2-e;
On-site combustion and upstream processing/extraction for power/diesel/natural gas/propane/gasoline = 16,206 tonnes CO2-e; and
Landfill disposal of residuals = 21,017 tonnes CO2-e.
Net calculated offsets = 213,217 tonnes CO2-e.
*2007 IPCC GWP = 25 for CH4, 298 for N2O
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Residential Recycling
Discussion
Residential Recycling
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Complexities of Carbon
Accounting in Recycling Cannot assume away transportation component emissions.
Carbon footprint of end use of recycled materials must be compared against:
Avoided emissions from landfilling of organic materials; and
Carbon footprint for displacement of virgin materials in end manufacturing.
Municipalities only play small part in the long recycling chain.
Long chain of custody for diversity and grades of recycled materials from initial separation to final recycled use means no one player will likely have all info necessary for calculation.
Fast moving/changing markets for recyclable materials.
What proportion of the carbon footprint of collection and sorting is assigned to what commodities?
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Newsprint Recycling Example
ONP6 vs. ONP8:
Less “outthrows” in ONP8, but greater effort required.
ONP8 however, can likely go to regional/NA mills vs.
overseas where it may be economical to re-sort the paper.
MRF operator’s incentives likely only returns vs. cost
(sorting and transportation), not carbon footprint.
Transportation costs disproportionate to actual GHG
emissions generated.
Downstream processing/manufacturing emission factors
(e.g., power) likely unknown to MRF operator.
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Waste Reduction Example:
Grasscycling
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Carbon Footprint of Grasscycling
Carbon footprint of grasscycling is due to
emissions from:
Production of potable water and chemical fertilizers
applied to a lawn to grow grass; and
Use and production of any fuels consumed in cutting
grass.
Carbon footprint of grasscycling can be compared
to carbon footprint of its alternatives.
The Residential Grass Cultivation System
Grow Grass
Cut Grass
Grass Clippings
Fertilizer
Water
Lawnmower
Energy
Landfill w/o LFG
Collection
Composting
Operation
Energy Inputs into Composting
Operation
Option (Baseline) 1: Landfilling Grass
Clippings
Option 3: Grasscycling
Option (Baseline) 2: Composting Grass
Clippings
System Boundary
Energy Inputs into Landfilling Operation
Sunlight
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Numbers for Comparative Calculation
180,000 single family households @ 250 m2 lawn
size, 354 kgs yearly production of clippings.
Average cutting every 2 weeks April-October w/
gasoline powered mowers, 0.2 L gasoline/cutting.
No watering of lawns, displacement of 25%
fertilizer (28-4-8) requirements on 50% of lawns.
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Alternative Baseline Scenario 1:
Landfill Disposal
Residential collection of clippings in 6.5 tonne payload vehicles, round trip distance of 80 kms to transfer station, 3.5 L diesel/km.
Transfer haul to landfill w/o LFG collection in 20 tonne payload long haul vehicles, round trip distance of 180 kms, 0.6 L diesel/km.
Pro-rated energy inputs (power, natural gas, diesel) into landfill operation.
GHG emissions from landfilling of grass.
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Alternative Baseline 2:
Central Composting
Residential collection as per landfilling
baseline.
Gross emission factors for centralized
composting as per City of Edmonton
operation.
Relative GHG Emissions for Residential Grass
Management in Edmonton
0
20000
40000
60000
80000
100000
120000
140000
Grasscycling Composting Disposal to Landfill
Metr
ic T
on
nes C
O2
129,037 tonnes CO2-e
20,777 tonnes CO2-e
1,758 tonnes CO2-e
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Hierarchy Comparison for
Residential Grass Management If the right-most bar on the graph (129,037 tonnes
CO2-e) indicates methane emissions that would result
from landfilling 63,270 tonnes of waste of grass
clippings, then emissions could be reduced by:
96,777 tonnes CO2-e with a 75% efficient LFG capture
system, a waste recovery activity
108,260 tonnes CO2-e by composting, a waste recycling
activity
127,279 tonnes CO2-e by grasscycling, a waste reduction
activity
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Summary and Conclusions
As per the grasscycling example, in general, the higher a practice is in the waste management hierarchy, the lower the carbon footprint.
Logical and accepted methodologies for determining carbon footprint of various waste management practices.
Difficult to accurately quantify emission reductions from residential recycling.
Numbers used in carbon footprint calculations (emission factors, GWP values) will change, more important is the chain of logic used to determine how to do the calculation.
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Questions???