Calculating Carbon Emission Effect of Waste Management Activities

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
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Higher Preference
Waste Management Hierarchy: the 4 Rs
Reduce
Reuse
Recycle
Recover

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.
CH 4 is main GHG of concern as CO 2 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 CH 4 emissions worldwide are attributed to
landfills.
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Methane Generation Potential, L o
L o = amount of CH 4 that can theoretically be produced
from landfilling one tonne of waste
L o = MCF x DOC x DOC f x F x (16/12) x 1000 kgs
CH 4 /tonne waste
Where L o = CH 4 generation potential, kgs/tonne of waste
MCF = CH 4 correction factor, fraction
DOC = degradable organic carbon, t C/t of waste
DOC f = fraction of DOC that dissimilates under landfill conditions
F = fraction of CH 4 in landfill gas
16/12 = stoichiometric factor for conversion of CH 4 to carbon
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Time Distribution of L o
Mass of material landfilled M, times L o yields
the maximum amount of methane that can be
generated from that material.
Applying a first order decay function (e -kt ) to
M x L o will give a time distribution to the
emissions.
Resulting relationship commonly known as
Scholl Canyon Model.
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Summation of Individual FOD Curves Over Time
Time period of
active landfilling
CH 4
Emissions
(Q)
Individual first order decay
(FOD) time distribution
curve for methane
generation
0 1 2
Time (Yrs)
100
∞

Numerical Approximation of FOD
Model Equation
n
Qt = ∑ 2k L o M i e -kt i
i=1
Where Q t = total LFG emission rate, volume/time
n = total time periods of waste placement
k = methane generation rate constant, time -1
L o = methane generation potential, volume/mass of waste
t i = age of the ith section of waste, time
M i = 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 CH 4 captured vs. generated.
Further 10% oxidation of CH 4 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 m 3 /day,
with average CH 4 content of 52%.
2011 data:
City Scholl Canyon model calculated 8,122 tonnes CH 4
generated.
Capital Power recorded 6,384 tonnes CH 4 captured.
Net emissions difference, counting flaring/power
generation and cover oxidation = 32,848 tonnes CO 2 -e.*
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*Using a GWP of 21 for CH 4

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 L o ].
Differences between above and emissions from a
baseline [landfilling of materials composted] are the
emission reductions [offsets] from the operation.
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Basic Composting System Boundary, Inputs
and Outputs
Waste Production
(households,
commercial)
Waste collection,
sorting,
transportation
Sorting
Landfill)
Recycle
Aerobic Conversion
Compost
On site use of
electricity
Electricity from grid
On site use by
equipment
Fuel (Diesel)
System Boundary Limit
End User
Adapted from CDM (2005)

Windrow Composting

Baseline Emissions
E baseline = [M delivered x (MCF)(DOC)(DOC F )(F)(16/12) –R][1-OX][GWP methane ]
Where E baseline = CH 4 emissions from landfilled waste in CO 2 equivalent (tonnes)
M delivered
MCF
DOC
DOC F
= waste delivered to composting facility (tonnes)
= methane correction factor
= 1 for managed landfills (IPCC default)
= degradable organic fraction of waste (tonne C/tonne waste)
= 0.19 for Alberta (calculated using Environment Canada data)
= fraction of degradable organic carbon dissimilated
= 0.77 (IPCC default)
F = fraction of LFG that is CH 4 , assumed to be 0.5
16/12 = stoichiometric factor (molecular weight fraction of CH 4 /C)
R = recovered landfill gas at baseline landfill (measured)
OX = landfill oxidation factor
= 0.1 for landfills with soil or compost covers (IPCC default)
GWP methane = global warming potential of methane of 25 (IPCC default)

Diesel Usage Emissions
E diesel = (F CO2 )(V diesel ) + (F CH4 )(V diesel )(GWP CH4 ) + (F N2O )(V diesel )(GWP N2O )
Where E diesel = direct GHG emissions from diesel combusion, kg CO 2 -e
F CO2
= emission factor for CO 2 emissions from diesel combustion
= 2.730 kg CO 2 per m 3 (CAPP value)
V diesel = volume of diesel gas consumed (m 3 )
F CH4
= emission factor for CH 4 emissions from diesel combustion
= 0.000133 kg CH 4 per m 3 (CAPP value)
GWP CH4 = global warming potential for CH 4 of 21 (IPCC default)
F N2O
= emission factor for N 2 O emissions from diesel combustion
= 0.0004 kg N 2 O per m 3 (CAPP value)
GWP N2O = global warming potential for N 2 O of 310 (IPCC default)

Diesel Production Emissions
E diesel,p = (F CO2,p )(V diesel ) + (F CH4,p )(V diesel )(GWP CH4 ) + (F N2O,p )(V diesel )(GWP N2O )
Where E diesel,p = upstream GHG emissions from diesel production, kg CO 2 -e
F CO2,p
= emission factor for CO 2 emissions from diesel combustion
= 0.138 kg CO 2 per m 3 (CAPP value)
V diesel = volume of diesel gas consumed (m 3 )
F CH4
= emission factor for CH 4 emissions from diesel production
= 0.0109 kg CH 4 per m 3 (CAPP value)
GWP CH4 = global warming potential for CH 4 of 21 (IPCC default)
F N2O
= emission factor for N 2 O emissions from diesel production
= 0.000004 kg N 2 O per m 3 (CAPP value)
GWP N2O = global warming potential for N 2 O of 310 (IPCC default)

ECF Example
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Collected
Mixed
Residential
MSW
Pre-processing
(sorting)
110,000 tonnes
Edmonton Composting Facility System
Boundary, Inputs and Outputs
ECF –
mechanical
plant
Primary Residuals 14,000 tonnes, 13.4%organic
Secondary Residuals 15,000 tonnes, 45.3%organic
On-site power
use
On-site natural
gas use
Electricity from
grid
Natural gas
Residues to
landfill w/ no
LFG
Collection
14,000,000 kWh
29,600 GJ
Compost curing
On-site diesel
use
Diesel fuel
483,900 L
10,000 tonnes
Collected waste
wood
On-site waste
wood chipping
On-site
gasoline use
On-site
propane use
Gasoline
Propane
1,280 L
1,740 m 3
Dewatered
municipal
biosolids
Biosolids/wood
chip mixing
Screening cured
compost
Tertiary Residuals 2,000 tonnes, 45.3%organic
Residues to
landfill w/ LFG
collection
Biosolids/wood
chip composting
System Boundary
Compost sales
to end users

Calculation of Emissions and Offsets
for the ECF*
Baseline emissions from landfilling feedstock =
263,340 tonnes CO 2 -e.
Project Emissions of 50,123 tonnes CO 2 -e:
Composting = 12,900 tonnes CO 2 -e;
On-site combustion and upstream processing/extraction for
power/diesel/natural gas/propane/gasoline = 16,206 tonnes
CO 2 -e; and
Landfill disposal of residuals = 21,017 tonnes CO2-e.
Net calculated offsets = 213,217 tonnes CO 2 -e.
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*2007 IPCC GWP = 25 for CH 4 , 298 for N 2 O

Residential Recycling
Discussion
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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.
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What proportion of the
carbon footprint of
collection and sorting
is assigned to what
commodities

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.
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The Residential Grass Cultivation System
System Boundary
Water
Sunlight
Fertilizer
Grow Grass
Lawnmower
Energy
Cut Grass
Option 3: Grasscycling
Grass Clippings
Energy Inputs into Landfilling Operation
Option (Baseline) 1: Landfilling Grass
Clippings
Landfill w/o LFG
Collection
Option (Baseline) 2: Composting Grass
Clippings
Composting
Operation
Energy Inputs into Composting
Operation

Numbers for Comparative Calculation
180,000 single family households @ 250 m 2 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.
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Metric Tonnes CO2
Relative GHG Emissions for Residential Grass
Management in Edmonton
140000
129,037 tonnes CO2-e
120000
100000
80000
60000
40000
20,777 tonnes CO2-e
20000
1,758 tonnes CO 2 -e
0
Grasscycling Composting Disposal to Landfill

Hierarchy Comparison for
Residential Grass Management
If the right-most bar on the graph (129,037 tonnes
CO 2 -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 CO 2 -e with a 75% efficient LFG capture
system, a waste recovery activity
108,260 tonnes CO 2 -e by composting, a waste recycling
activity
127,279 tonnes CO 2 -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
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