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GREENHOUSE GAS EMISSIONS FROM
MANAGEMENT OF SELECTED MATERIALS IN
MUNICIPAL SOLID WASTE
FINAL REPORT
Prepared for the U.S. Environmental Protection Agency
under EPA Contract No. 68-W6-0029
September 1998
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TABLE OF CONTENTS
EXECUTIVE SUMMARY: BACKGROUND AND FINDINGS ES-1
ES.l GREENHOUSE GASES AND CLIMATE CHANGE ES-1
ES.2 WHAT IS THE UNITED STATES DOING ABOUT CLIMATE CHANGE? ES-2
ES.3 WHAT IS THE RELATIONSHIP OF MUNICIPAL SOLID WASTE TO
GREENHOUSE GAS EMISSIONS? ES-3
ES.4 WHY EPA PREPARED THIS REPORT AND HOW IT WILL BE USED ES-4
ES.5 HOW WE ANALYZED THE IMPACT OF MUNICIPAL SOLID WASTE
ON GREENHOUSE GAS EMISSIONS ES-5
ES.6 RESULTS OF THE ANALYSIS ES-10
ES.7 LIMITATIONS OF THE ANALYSIS ES-16
1. METHODOLOGY 1
1.1 INTRODUCTION 1
1.2 THE OVERALL FRAMEWORK:
A STREAMLINED LIFE CYCLE INVENTORY 1
1.3 THE REVIEW PROCESS 2
1.4 MSW MATERIALS CONSIDERED IN THE STREAMLINED LIFE CYCLE
INVENTORY 3
1.5 KEY INPUTS AND BASELINES FOR THE STREAMLINED
LIFE CYCLE INVENTORY 4
1.6 HOW THESE INPUTS ARE TALLIED AND COMPARED ....7
1.7 SUMMARY OF THE LIFE CYCLE STAGES 9
2. RAW MATERIALS ACQUISITION AND MANUFACTURING 15
2.1 GHG EMISSIONS FROM ENERGY USE IN RAW MATERIALS
ACQUISITION AND MANUFACTURING 15
2.2 NON-ENERGY GHG EMISSIONS FROM MANUFACTURING
AND RAW MATERIALS ACQUISITION .: 20
2.3 RESULTS 20
2.4 LIMITATIONS OF THE ANALYSIS '. 21
3. FOREST CARBON SEQUESTRATION 35
3.1 * MODELING FRAMEWORK 38
3.2 THE NORTH AMERICAN PULP AND PAPER (NAPAP) MODEL 39
3.3 THE TIMBER ASSESSMENT MARKET MODEL (TAMM)
AND THE AGGREGATE TIMBERLAND ASSESSMENT SYSTEM (ATLAS) 44
3.4 THE FOREST CARBON MODEL (FORCARB) 47
3.5 THE HARVESTED CARBON MODEL (HARVCARB) 49
3.6 RESULTS 52
3.7 LIMITATIONS OF THE ANALYSIS 56
4. SOURCE REDUCTION AND RECYCLING 61
4.1 GHG IMPLICATIONS OF SOURCE REDUCTION 61
4.2 GHG IMPLICATIONS OF RECYCLING 63
4.3 SOURCE REDUCTION WITH MATERIAL SUBSnTTUTION 66
4.4 LIMITATIONS OF THE ANALYSIS 67
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5. COMPOSTING 71
5.1 POTENTIAL GREENHOUSE GAS -EMISSIONS .71
5.2 POTENTIAL CARBON SEQUESTRATION 72
5.3 NET GHG EMISSIONS FROM COMPOSTING .'. 76
5.4 LIMITATIONS OF THE ANALYSIS 76
6. COMBUSTION 79
6.1 METHODOLOGY 81
6.2 RESULTS 89
6.3 LIMITATIONS OF THE ANALYSIS : 92
7. LANDFILLING 95
7.1 EXPERIMENTAL VALUES FOR METHANE GENERATION
AND CARBON SEQUESTRATION 96
7.2 FATES OF LANDFILL METHANE: CONVERSION TO CO2, EMISSIONS,
AND FLARING OR COMBUSTION WITH ENERGY RECOVERY 99
7.3 NET GHG EMISSIONS FROM LANDFILLING 101
7.4 LIMITATIONS OF THE ANALYSIS 102
8. ACCOUNTING FOR EMISSION REDUCTIONS Ill
8.1 GHG EMISSIONS FOR EACH WASTE
MANAGEMENT OPTION 111
8.2 APPLYING EMISSION FACTORS " 113
BACKGROUND DOCUMENTS (Available in the docket in the RCRA Information Center)
DOCUMENT A - BACKGROUND DATA SUBMITTED BY FRANKLIN ASSOCIATES, Ltd.
ATTACHMENT 1 - A PARTIAL LIFE CYCLE INVENTORY OF PROCESS
AND TRANSPORTATION ENERGY FOR BOXBOARD AND PAPER
TOWELS
DOCUMENT B - BACKGROUND DATA SUBMITTED BY THE TELLUS INSTITUTE
DOCUMENT C - REVIEW PROCESS FOR THE REPORT
' DOCUMENT D - COMMENT-RESPONSE DOCUMENT
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EXECUTIVE SUMMARY: BACKGROUND AND FINDINGS
An important environmental challenge facing the United States (US) is management of
municipal solid waste (MSW). In 1996, the US generated 210 million tons of MSW;1 per-capita
MSW generation rates have risen throughout most of the last decade. At the same time, the US
recognizes climate change as a potentially serious issue, and is embarking on a number of actions
to reduce the emissions of greenhouse gases (GHGs) that can cause it. This report examines how
the two issues - MSW management and climate change — are related, by presenting material-
specific GHG emission factors for various waste management options.
Among the efforts to slow the potential for climate change are measures to reduce
emissions of carbon dioxide from energy use, reduce methane emissions, and change forestry
practices to promote long-term storage of carbon in trees. Different management options for
MSW provide many opportunities to affect these same processes, directly or indirectly. This
report integrates, for the first time, a wealth of information on GHG implications of various
MSW management options for some of the most common materials in MSW and for mixed
MSW and mixed recyclables. The report's findings may be used to support voluntary reporting
of emission reductions from waste management practices.
ES.1 GREENHOUSE GASES AND CLIMATE CHANGE
Climate change is a serious international environmental concern and the subject of much
research and debate. Many, if not most, of the readers of this report will have a general
understanding of the greenhouse effect and climate change. However, for those who are not
familiar with the topic, a brief explanation follows.2
A naturally occurring shield of "greenhouse gases" (primarily water vapor, carbon
dioxide, methane, and nitrous oxide), comprising 1 to 2 percent of the Earth's atmosphere, traps
radiant heat from the Earth and helps warm the planet to a comfortable, livable temperature
range. Without this natural "greenhouse effect," the average temperature on Earth would be
approximately 5 degrees Fahrenheit, rather than the current 60 degrees Fahrenheit.3
1 U.S. EPA Office of Solid Waste, Characterization of Municipal Solid Waste in the United
States:-1997 Update, EPA 530-R-9-001, p. 26.
2 For more detailed information on climate change, please see The Draft 1998 Inventory of US
Greenhouse Gas Emissions and Sinks: 1990-1996, (http://www.epa.gov/globalwarming/inventory/1998-
inv.html) (March 1998); and Climate Change 1995: The Science of Climate Change (J.T. Houghton, etal,
eds.; Intergovernmental Panel on Climate Change [IPCC]; published by Cambridge University Press,
1996). To obtain a list of additional documents addressing climate change, call EPA's Climate Change
"FAX on Demand" at (202) 260-2860 or access EPA's global wanning web site at
www.epa.gov/globalwarming.
3 Climate Change 1995: The Science of Climate Change (op. cit.\ pp. 57-58.
ES-1
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Many scientists, however, are alarmed by a significant increase in the concentration of
carbon dioxide and other GHGs in the atmosphere. Since the pre-industrial era, atmospheric
concentrations of carbon dioxide have increased by nearly 30 percent and methane
concentrations have more than doubled. There is a growing international scientific consensus that
this increase has been caused, at least in part, by human activity, primarily the burning of fossil
fuels (coal, oil, and natural gas) for such activities as generating electricity and driving cars.4
Moreover, there is a growing consensus in international scientific circles that the buildup
of carbon dioxide and other GHGs in the atmosphere will lead to major environmental changes
such as: (1) rising sea levels (that may flood coastal and river delta communities); (2) shrinking
mountain glaciers and reduced snow cover (that may diminish fresh water resources), (3) the
spread of infectious diseases and increased heat-related mortality, (4) impacts to ecosystems and
possible loss in biological diversity, and (5) agricultural shifts such as impacts on crop yields and
productivity. Although it is difficult to reliably detect trends in climate due to natural variability,
the best current predictions suggest that the rate of climate change attributable to GHGs will far
exceed any natural climate changes that have occurred during the last 10,000 years.5
Many of these changes appear to be occurring already. Global mean surface temperatures
have already increased by about 1 degree Fahrenheit over the past century. A reduction in the
Northern Hemisphere's snow cover, a decrease in Arctic sea ice, a rise in sea level, and an
increase in the frequency of extreme rainfall events have all been documented.6
Such important environmental changes pose potentially significant risks to humans,
social systems, and the natural world. Of course, many uncertainties remain regarding the precise
timing, magnitude, and regional patterns of climate change and the extent to which mankind and
nature can adapt to any changes. It is clear, however, that changes will not be easily reversed for
many decades or even centuries because of the long atmospheric lifetimes of the GHGs and the
inertia of the climate system.
ES.2 WHAT IS THE UNITED STATES DOING ABOUT CLIMATE CHANGE?
In 1992, world leaders and citizens from some 200 countries met in Rio de Janeiro,
Brazil to confront global ecological concerns. At this "Earth Summit", 154 nations, including
the United States, signed the Framework Convention on Climate Change, an international
agreement to address the danger of global climate change. The objective of the Convention is to
stabilize GHG concentrations in the atmosphere at a level, and over a time frame, that will
minimize man-made climate disruptions.
By signing the Convention, countries make a voluntary commitment to reduce GHGs or
take other actions to stabilize emissions of GHGs at 1990 levels. All parties to the Convention
are also required to develop, and periodically update, national inventories of their GHG
emissions. The US ratified the Convention in October 1992. One year later, President Clinton
issued the US Climate Change Action Plan (CCAP), which called for cost-effective domestic
4 Ibid., pp. 3-5.
s Ibid., pp. 6, 29-30, 156, and 371-372.
4 Ibid., pp. 26, 29-30, 156, and 171.
ES-2
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actions and voluntary cooperation with states, local governments, industry, and citizens to reduce
GHG emissions. •
Countries that ratified the Framework Convention on Climate Change met in Kyoto,
Japan in December 1997, where they agreed to reduce global greenhouse gas emissions and set
binding targets for developed nations. (For example, the emissions target for the US would be 7
percent below 1990 levels.) As of the publication of this report, the Kyoto agreement remains to
be signed by the President and ratified by the US Senate; meanwhile, EPA continues to promote
voluntary measures to reduce GHG emissions begun under the CCAP. The countries that ratified
the Framework Convention will meet again in Buenos Aires in November, 1998, where the US
will attempt to secure meaningful participation by developing countries.
The CCAP outlines over 50 voluntary initiatives to reduce GHG emissions in the US.
One of the initiatives calls for accelerated source reduction and recycling of municipal solid
waste through combined efforts by EPA, the Department of Energy, and the Department of
Agriculture. Another waste related initiative is the Landfill Methane Outreach Program, which
aims to reduce landfill methane emissions by facilitating the development of landfill gas
utilization projects.7
ES.3 WHAT IS THE RELATIONSHIP OF MUNICIPAL SOLID WASTE TO
GREENHOUSE GAS EMISSIONS?
What does municipal solid waste have to do with rising sea levels, higher temperatures,
and GHG emissions? For many wastes, the materials that we dispose represent what is left over
after a long series of steps including: (1) extraction and processing of raw materials; (2)
manufacture of products; (3) transportation of materials and products to markets; (4) use by
consumers; and (5) waste management.
At virtually every step along this "life cycle," the potential exists for GHG impacts.
Waste management affects GHGs by affecting one or more of the following:
(1) Energy consumption (specifically, combustion of fossil fuels) associated with
making, transporting, using, and disposing the-product or material that becomes
a waste.
(2) Non-energv-related manufacturing emissions, such as the carbon dioxide
released when limestone is converted to lime (which is needed for aluminum and
steel manufacturing)..
(3) Methane emissions from landfills where the waste is disposed.
(4) Carbon sequestration, which refers to natural or man-made processes that
remove carbon from the atmosphere and store it for long time periods or
permanently. A store of sequestered carbon (e.g., a forest or coal deposit) is
known as a carbon sink.
7 The Landfill Methane Outreach Program is a voluntary partnership between the EPA, state
agencies, landfill gas-to-energy developers and energy users. The program has an Internet home page
(http://www.epa.gov/landfill.html), and can be reached via a toll-free hotline number (1-800-782-7937).
ES-3
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The first three mechanisms add GHGs to the atmosphere and contribute to global
warming. The fourth - carbon sequestration - reduces GHG concentrations by removing carbon
dioxide from the atmosphere. Forests are one mechanism for sequestering carbon; if more wood
is grown than is removed (through harvest or decay), the amount of carbon stored in trees
increases, and thus carbon is sequestered.
Different wastes and waste management options have different implications for energy
consumption, methane emissions, and carbon sequestration. Source reduction and recycling of
paper products, for example, reduce energy consumption, decrease combustion and landfill
emissions, and increase forest carbon sequestration.
ES.4 WHY EPA PREPARED THIS REPORT AND HOW IT WILL BE USED
Recognizing the potential for source reduction and recycling of municipal solid waste to
reduce GHG emissions, EPA included a source reduction and recycling initiative in the original
1994 CCAP. At that time, EPA estimated that its portion of the source reduction and recycling
initiative could reduce annual GHG emissions by roughly 5.6 million metric tons of carbon
equivalent (MTCE) by the year 2000, or about 5 percent of the overall goal of the Action Plan.
To make these projections, EPA used limited data on energy consumption and forest carbon
sequestration to estimate how a 5 percent increase in both source reduction and recycling would
affect GHG emissions in 2000.
It was clear then that a rigorous analysis would be needed to more accurately gauge the
total GHG emission reductions achievable through source reduction and recycling. Moreover, it
was clear that all of the options for managing MSW should be considered. By addressing a
broader set of MSW management options, a more comprehensive picture of the GHG benefits of
voluntary actions in the waste sector could be determined and the relative GHG impacts of
various waste management approaches could be assessed. To this end, the Office of Policy and
the Office of Solid Waste launched a major research effort.
This research effort has been guided by contributions from many reviewers participating
in three review cycles (as described in Background Document C). The first draft report was
reviewed in 1995 by 20 EPA analysts from four offices (Air and Radiation; Policy; Research and
Development; and Solid Waste) as well as analysts from the US Department of Energy and US
Department of Agriculture, Forest Service. Comments resulting from these reviews were
incorporated into a second draft of the report, completed in May 1996.
The 1996 draft was distributed to four researchers with academic and consulting
backgrounds for a more intensive, external peer review. Based on their comments, another draft
of the report was completed in March of 1997.
In March, 1997, EPA published the draft research in a report entitled Greenhouse Gas
Emissions from Municipal Waste Management: Draft Working Paper (EPA530-R-97-010). As
described in an accompanying Federal Register notice, public comment was solicited on the draft
working paper.
This final report reflects comments from 23 individuals, representing trade associations,
universities, industry, state offices, EPA offices, and other entities. Among the groups that
provided detailed comments were:
ES-4
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• The American Forest and Paper Association,.
• The American Plastics Council, '
• The Steel Recycling Institute,
• The Integrated Waste Services Association,
• The Minnesota Office of Environmental Assistance, and
• The Missouri Department of Natural Resources.
Each comment on the draft working paper is specifically discussed in a comment response
document, which is available in the public docket (F-97-GGEA-FFFFF). For each comment
received, the comment response document summarizes both the comment and EPA's response.
Among the changes made as a result of this review, EPA
• added two materials to the analysis—mixed paper and glass,
• revised system efficiencies for waste combustors, and provided a separate
characterization of refuse-derived fuel (RDF) as a category of combustion,
• based GHG reductions from displaced electricity on GHGs from fossil-fuel-fired
generation, rather than from the national average mix of fuels.
Each of these changes is discussed in more detail later in this report. In addition, this report
updates many of the inputs to the calculations (such as the global warming potential for various
greenhouse gases), and uses more recent information on waste composition and recycling rates.
The primary application of the GHG emission factors in this report is to support climate
change mitigation accounting for waste management practices. Organizations interested in
quantifying and voluntarily reporting GHG emission reductions associated with waste
management practices may use these emission factors for that purpose. In conjunction with the
Department of Energy, EPA has used these emission factors to develop guidance for voluntary
reporting of GHG reductions, as authorized by Congress in Section 1605 (b) of the Energy Policy
Act of 1992. EPA also plans to use these emission factors to evaluate its progress in reducing
US GHG emissions—by promoting source reduction and recycling through voluntary programs
such as WasteWi$e and Pay-as-You-Throw (PAYT)—as part of the-US CCAP. The
methodology presented in this report may also assist other countries involved in developing GHG
emissions estimates for their solid waste streams.8
ES.5 HOW WE ANALYZED THE IMPACT OF MUNICIPAL SOLID WASTE ON
GREENHOUSE GAS EMISSIONS
To measure the GHG impacts of municipal solid waste (MSW), one must first decide
which wastes to analyze. We surveyed the universe of materials and products found in MSW and
determined which were most likely to have the greatest impact on GHGs. These determinations
were based on (1) the quantity generated, (2) differences in energy use for manufacturing a
product from virgin versus recycled inputs, and (3) the potential contribution of materials to
methane generation in landfills. By this process, we limited the analysis to the following 11
items:
8 Note that waste composition and product life cycles vary significantly among countries. This
report may assist other countries by providing a methodologic framework and benchmark data for
developing GHG emission estimates for their solid waste streams.
ES-5
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newspaper,
office paper,
corrugated cardboard,
aluminum cans,
steel cans,
glass containers,
HDPE (high density polyethylene) plastic,
LDPE (low density polyethylene) plastic,
PET (polyethylene terephthalate) plastic,
food scraps, and
yard trimmings.
The foregoing materials constitute 55
percent, by weight, of municipal solid waste, as
shown in Exhibit ES-1.9 We also examined the
GHG implications of managing mixed MSW,
mixed recyclables, and mixed paper.
• Mixed MSW is comprised of the
waste material typically discarded by
households and collected by curbside
collection vehicles; it does not
include white goods or industrial
waste. This report analyzes mixed
MSW on an "as disposed" (rather
than "as generated") basis.
• Mixed recyclables are materials that
are typically recycled. As used in
this report, the term includes the
items listed in Exhibit ES-1, except
food scraps and yard trimmings. The
emission factors reported for mixed
recyclables represent the average
GHG emissions for these materials,
weighted by the tonnages at which
they are recycled.
Exhibit ES-1
Percentage of 1996 US Generation of
MSW for Materials in This Report
Material
Newspaper
Office paper
Corrugated cardboard
Aluminum cans
Steel cans
Glass containers
HDPE plastic*
LDPE plastic*
PET plastic*
Food scraps
Yard trimmings
TOTAL
Percentage of
MSW Generation
(by Weight)
5.9%
3.2%
13.8%
0.8%
1.3%
5.3%
0.6%
0.01%
0.5%
10.4%
13.4%
55%
Source: Franklin Associates, Ltd.,
Characterization of Municipal Solid Waste in the
United States: 1997 Update. EPA 530-R-98-007
(May 1998)
* Based on blow-molded containers.
Mixed paper is recycled in large quantities, and is an important class of scrap
material in many recycling programs. However, it is difficult to present a single
definition of mixed paper because each mill using recovered paper defines its own
supply which varies with the availability and price of different grades of paper.
Therefore, for purposes of this report, we identified three different definitions for
Note that these data are based on national averages. The composition of solid waste varies
locally and regionally; local or state-level data should be used when available. In recognition of the
variability in local conditions, EPA is developing the WAste Reduction Model (WARM), which may be
used to estimate the GHG emissions of MSW management actions on a local and state level. For more
information on the WARM model, contact the RCRA Hotline at 1-800-424-9346.
ES-6
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mixed paper according to their dominant source—broad (general sources), office,
and residential. •
Next, we developed a streamlined life cycle inventory for each of the selected materials.
Our analysis is streamlined in the sense that it examines GHG emissions only, and is not a more
comprehensive environmental analysis of all emissions from municipal solid waste management
options.10
We focused on those aspects of the life cycle that have the potential to emit GHGs as
materials change from their raw states, to products, to waste. Exhibit ES-2 shows the steps in the
life cycle at which GHGs are emitted, carbon sequestration is affected, and utility energy is
displaced. As shown, we examined the potential for these effects at the following points in a
product's life cycle:
• raw material acquisition (fossil fuel energy and other emissions, and change in forest
carbon sequestration);
• manufacturing (fossil fuel energy emissions); and
• waste management (carbon dioxide emissions associated with combustion and
methane emissions from landfills; these emissions are offset to some degree by
avoided utility fossil fuel use and carbon sequestration in landfills).
At each of these points, we also considered transportation-related energy emissions.
GHG emissions associated with electricity used in the raw materials acquisition and
manufacturing steps are estimated based on the current mix of energy sources, including fossil
fuels, hydropower, and nuclear power. However, estimates of GHG emission reductions
attributable to utility emissions avoided from waste management practices are based solely on the
reduction of fossil fuel use.11
We did not analyze the GHG emissions associated with consumer use of products
because energy use for the selected materials is small (or zero) at this point in the life cycle. In
addition, the energy consumed during use would be approximately the same whether the product
was made from virgin or recycled inputs.
To apply the GHG estimates developed in this report, one must compare a baseline
scenario with an alternative scenario, on a life-cycle basis. For example, one could compare a
baseline scenario, where 10 tons of office paper is manufactured, used, and landfilled, to an
alternative scenario, where 10 tons is manufactured, used, and recycled.
10 EPA' s Office of Research and Development (ORD) is performing a more extensive application
of life cycle assessment for various waste management options for MSW. ORD's analysis will inventory a
broader set of emissions (air, water, and waste) associated with these options. For more information on this
effort, go to their project website at http://www.epa.gov/docs/crb/apb/apb.htm.
" We adopted this approach based on suggestions from several commenters who argued that fossil
fuels should be regarded as the marginal fuel displaced by waste-to-energy and landfill gas recovery
systems.
ES-7
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Exhibit ES-2
GHG Sources and Sinks Associated with Materials in the MSW Stream
Inputs
Ore, trees,
petroleum,
energy, etc.
Energy
( Recycling
Energy
Life Cycle Stage1 GHG Emissions/Carbon Sinks2
Energy-related emissions
Non-energy related emissions
Change in carbon storage in forests
Energy-related emissions
(captures process and transportation energy
associated with recycling)
'Note that source reduction affects ail stages in the life cycle.
Alt He cycle stages analyzed Include transportation energy-related emissions.
Energy-related emissions
Change in carbon storage in soils
CO, emissions from plastics
N,O emissions
Credit for avoided fossil fuel use
CKi emissions
-Uncontrolled
-Flared or recovered for energy (converted to CO)
-Credit for avoided fossil fuel use
Credit for Carbon in long-term storage.
In calculating emissions for the scenarios, two different reference points can be used:
• With a "raw material extraction" reference point (i.e., cradle-to-grave perspective),
one can start at the point of raw material acquisition as the "zero point" for
emissions, and add all emissions (and deduct sinks) from that point on through the
life cycle.
• With a "waste generation" reference point (solid waste manager's perspective), one
can begin accounting for GHG emissions at the point of waste generation. All
subsequent emissions and sinks from waste management practices are then
accounted for. Changes in emissions and sinks from raw material acquisition and
manufacturing processes are captured to the extent that certain waste management
practices (i.e., source reduction and recycling) impact these processes.
When developing an emission factor to account for GHG emissions from a waste management
activity, the key question to ask is "What is the baseline management practice?" Because it is the
difference in emissions between the baseline and alternate scenarios that is meaningful, using
raw material extraction or waste generation reference points yields the same results. The March
1997 Draft Working Paper used the raw material extraction reference point to display GHG
emissions because it is most consistent with standard life cycle inventory accounting techniques.
Several commenters pointed out that solid waste decision-makers tend to view raw materials
ES-8
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acquisition and manufacturing as beyond their control, and suggested that a waste generation
GHG accounting approach would provide more clarity for evaluating waste management options.
Thus, this report uses the waste generation approach, and defines a standard raw material
acquisition and manufacturing step for each material as consisting of average GHG emissions
based on the current mix of virgin and recycled inputs. This standard raw material acquisition
and manufacturing step is used to estimate the upstream impacts of source reduction and
recycling.
Exhibit ES-3 shows how the GHG sources and sinks are affected by each waste
management strategy using the waste generation reference point. For example, the top row of the
exhibit shows that source reduction12 (1) reduces GHG emissions from raw materials acquisition
and manufacturing; (2) results in an increase in forest carbon sequestration; and (3) does not
result in GHG emissions from waste management. The sum of emissions (and sinks) across all
steps in the life cycle represents net emissions.
12 In this analysis, the source reduction techniques we analyze involve using less of a given
product without using more of some other product - e.g., making aluminum cans with less aluminum
("lightweighting"); double-sided rather than single-sided photocopying; or reuse of a product. We did not
consider source reduction of one product that would be associated with substitution by another product -
e.g., substituting plastic boxes for corrugated paper boxes. Nor did we estimate the potential for source
reduction of chemical fertilizers and pesticides with increased production and use of compost. For a
discussion of source reduction with material substitution, please see section 4.3.
ES-9
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Exhibit ES-3
Components of Net Emissions for Various Municipal Solid Waste Management Strategies
Municipal
Solid Waste
Management
Strategy
Source Reduction
Recycling
Composting (food
scraps, yard
trimmings)
Combustion
Landfilling
Greenhouse Gas Sources and Sinks
Raw Materials Acquisition and
Manufacturing
Decrease in GHG emissions,
relative to the baseline of
manufacturing
Decrease in GHG emissions due to
lower energy requirements
(compared to manufacture from
virgin inputs) and avoided process
non-energy GHGs
No emissions/sinks
No change
No change
Change in Forest or Soil
Carbon Storage
Increase in forest carbon
storage
Increase in forest carbon
storage
Increase in soil carbon
storage
No change
No change
Waste Management
No emissions/sinks
Process and transportation
emissions associated with
recycling are counted in the
manufacturing stage
Compost machinery emissions
and transportation emissions
Nonbiogenic CC>2, N2O
emissions, avoided utility
emissions, and transportation
emissions
Methane emissions, long-term
carbon storage, avoided utility
emissions, and transportation
emissions
ES.6 RESULTS OF THE ANALYSIS
Management of municipal solid waste presents many opportunities for GHG emission
reductions. Source reduction and recycling can reduce GHG emissions at the manufacturing
stage, increase forest carbon storage, and avoid landfill methane emissions. When waste is
combusted, energy recovery displaces fossil fuel-generated electricity from utilities (thus
reducing GHG emissions from the utility sector), and landfill methane emissions are avoided.
Landfill methane emissions can be reduced by using gas recovery systems and by diverting
organic materials from the landfill.
In order to support a broad portfolio of climate change mitigation activities covering a
broad scope of greenhouse gases, many different emission estimation methodologies will need to
be employed. The primary result of this research is the development of material-specific GHG
emission factors which can be used to account for the climate change benefits of waste
management practices. A spreadsheet accounting tool, the Waste Reduction Model (WARM), is
being developed to allow for customizing of emission factors based on key variables which may
better reflect local conditions.
Exhibit ES-4 presents the GHG impacts of source reduction, recycling, composting,
combustion, and landfilling, on a per-ton managed basis, for the individual materials, mixed
waste, and mixed recyclables, using the waste generation reference point. For comparison,
Exhibit ES-5 shows the same results, using the raw material extraction reference point. In these
ES-10
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tables, emissions for one ton of a given material are presented across different management
options.13 The life cycle GHG emissions for each- of the first four waste management strategies -
source reduction, recycling, composting, and combustion - are compared to the GHG emissions
from landfilling in Exhibit ES-6. This exhibit shows the GHG values for each of the first four
management strategies, minus the GHG values for landfilling. With this exhibit, one may
compare the GHG emissions of changing management of one ton of each material from
landfilling (often viewed as the baseline waste management strategy) to one of the other waste
management options.
All values shown in Exhibit ES-4 through ES-6 are for national average conditions (e.g.,
average fuel mix for raw material acquisition and manufacturing using recycled inputs; typical
efficiency of a mass burn combustion unit; national average landfill gas collection rates). GHG
emissions are sensitive to some factors that vary on a local basis, and thus site-specific emissions
willdiffer from those summarized here.
Following is a discussion of the principal GHG emissions and sinks for each waste
management practice and effect they have on the emission factors:
• Source reduction, generally speaking, represents an opportunity to reduce GHG
emissions in a significant way.14 The reduction in energy-related CO2 emissions
from the raw material acquisition and manufacturing process, and the absence of
emissions from waste management, combine to reduce GHG emissions more than all
other options.
• Recycling generally has the second lowest GHG emissions. For most materials,
recycling reduces enery-related CC^ emissions in the manufacturing process
(although not as dramatically as source reduction) and avoids emissions from waste
management. Paper recycling increase storage of forest carbon.
13 Note that the difference between any two values for a given material in Exhibit ES-4 (i.e.,
emissions for the same material in two waste management options) is the same as the difference between the
two corresponding values in Exhibit ES-5.
14 As noted above, the only source reduction strategy analyzed in this study is lightweighting.
Consequently, the results shown here do not directly apply to material substitution.
ES-11
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Exhibit ES-4
Net GHG Emissions from Source Reduction and MSW Management Options
Emissions Counted from a Waste Generation Reference Point (MTCE/Ton)1
Material
Newspaper
Office Paper
Corrugated Cardboard
Mixed Paper
Broad Definition
Residential Definition
Office Paper Definition
Aluminum Cans
Steel Cans
Glass
HOPE
LDPE
PET
Food Scraps
Yard Trimmings
Mixed MSW as Disposed
Mixed Recyclables
Source
Reduction2
-0.91
-1.03
-0.78
NA
NA
NA
-2.98
-0.84
-0.14
-0.61
-0.89
-0.98
NA
NA
NA
NA
Recycling
-0.86
-0.82
-0.70
-0.67
-0.67
-0.84
-3.88
-0.57
-0.08
-0.37
-0.49
-0.62
NA
NA
NA
-0.76
Composting3
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
0.00
0.00
NA
NA
Combustion4
- -0.22
-0.19
-0.19
-0.19
-0.19
-0.18
0.03
-0.48
0.02
0.21
0.21
0.24
-0.05
-0.07
-0.04
-0.18
Landfilling5
-0.23
0.53
0.04
0.06
0.03
0.10
0.01
0.01
0.01
0.01
0.01
0.01
0.15
-0.11
-0.02
0.03
Note that totals may not add due to rounding and more digits may be displayed than are significant.
NA: Not applicable, or in the case of composting of paper, not analyzed.
1MTCE/ton: Metric tons of carbon equivalent per short ton of material. Material tonnages are on an as-managed (wet weight) basis.
^Source reduction assumes initial production using the current mix of virgin and recycled inputs.
JThere is considerable uncertainty in our estimate of net GHG emissions from composting; the values of zero are plausible values
based on assumptions and a bounding analysis.
Values are for mass burn facilities with national average rate of ferrous recovery.
5Values reflect projected national average methane recovery in year 2000.
ES-12
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Exhibit ES-5
Net GHG Emissions from Source Reduction and MSW Management Options
Emissions Counted from a Raw Materials Extraction Reference Point (MTCE/Ton)
Material
Newspaper
Office Paper
Corrugated Cardboard
Mixed Paper
Broad Definition
Residential Definition
Office Paper Definition
Aluminum Cans
Steel Cans
Glass
HOPE
LDPE
PET
Food Waste
Yard Waste
Mixed MSW as Disposed
Mixed Recyclables
Source
Reduction1
-0.43
-0.50
-0.38
NA
NA
NA
0.00
0.00
0.00
0.00
0.00
0.00
NA
NA
NA
NA
Recycling2
-0.38
-0.30
-0.30
-0.21
-0.22
-0.33
-0.90
0.26
0.06
0.24
0.40
0.36
NA
NA
NA
-0.26
Composting2
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
0.00
0.00
NA
NA
Combustion2
0.26
0.34
0.21
0.26
0.26
0.33
3.01
0.35
0.17
0.81
1.10
1.21
-0.05
-0.07
-0.04
0.33
Landfilling2
0.25
1.06
0.44
0.51
0.48
0.61
3.00
0.85
0.15
0.62
0.90
0.99
0.15
-0.11
-0.02
0.53
• -if •••-•• — —-JJ..— I I -WJ M« MIWfrflMJ WU H IM1 I t*l \S WlMI IIIIWCU 111
NA: Not applicable, or in the case of composting of paper, not analyzed.
1Source reduction assumes initial production using the current mix of virgin and recycled inputs.
includes emissions from the initial production of the material being managed, except for food waste, yard waste, and
mixed MSW.
ES-13
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Exhibit ES-6
Greenhouse Gas Emissions of MSW Management Options Compared to Landfilling1
(MTCE/Ton)
Material
Newspaper
Office Paper
Corrugated Cardboard
Mixed Paper
Broad Definition
Residential Definition
Office Paper Definition
Aluminum Cans
Steel Cans
Glass
HOPE
LDPE
PET
Food Scraps
Yard Trimmings
Mixed MSW as Disposec
Mixed Recyclables
Source Reduction2
Net Emissions
Minus Landfilling Net Emissions
-0.68
-1.56
-0.82
NA
NA
NA
-3.00
-0.85
-0.15
-0.62
-0.90
-0.99
NA
NA
NA
NA
Recycling Net Emissions
Minus Landfilling
Net Emissions
-0.63
-1.35
•0.74
-0.73
-0.69
-0.95
-3.89
-0.58
-0.09
-0.38
-0.51
-0.63
NA
NA
NA
-0.79
Composting3 Net C
Minus Landfilling
Net Emissions
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
-0.15
0.11
NA
NA
Combustion4 Net Emissions
Minus Landfilling
Net Emissions
0.01
-0.72
-0.23
-0.25
-0.22
-0.28
0.02
-0.49
0.01
0.20
0.20
0.22
-0.20
0.04
-0.02
-0.20
NA: Not applicable, or in the case of composting of paper, not analyzed.
Values for landfilling reflect projected national average methane recovery in year 2000.
2Source reduction assumes initial production using the current mix of virgin and recycled inputs.
^Calculation is based on assuming zero net emissions for composting.
'Values are for mass burn facilities with national average rate of ferrous recovery.
ES-14
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• Composting is a management option for food scraps and yard trimmings. The net
GHG emissions from composting are lower than landfilling for food scraps
(composting avoids methane emissions), and higher than landfilling for yard
trimmings (landfilling is credited with the carbon storage that results from failure of
certain yard trimmings to degrade fully in landfills). Overall, given the uncertainty
in the analysis, the emission factors for composting or combusting these materials
are similar.
• The net GHG emissions from combustion and landfilling are similar for mixed
MSW. Because, in practice, combustors and landfills manage a mixed wastestream,
net emissions are determined more by technology factors (e.g., landfill gas collection
system efficiency, combustion energy conversion efficiency) than by material
specificity. Material-specific emissions for landfills and combustors provide a basis
for comparing these options with source reduction, recycling, and composting.
The ordering of combustion, landfilling, and composting is affected by (1) the GHG inventory
accounting methods, which do not count COi emissions from sustainable biogenic sources,15 but
do count emissions from sources such as plastics, and (2) a series of assumptions on
sequestration, future use of methane recovery systems, landfill gas recovery system efficiency,
ferrous metals recovery, and avoided utility fossil fuels. On a site-specific basis, the ordering of
results between a combustor and a landfill could be different from the ordering provided here,
which is based on national average results.
We conducted sensitivity analyses to examine the GHG emissions from landfilling under
varying assumptions about (1) the percentage of landfilled waste sent to landfills with gas
recovery and (2) methane oxidation rate and gas collection system efficiency. The sensitivity
analyses demonstrate that the results for landfills are very sensitive to these factors, which are
site-specific. Thus, using a national average value when making generalizations about
emissions from landfills masks some of the variability that exists from site to site.
The scope of this report is limited to developing emission factors that can be used to
evaluate GHG implications of solid waste decisions. We do not analyze policy options in this
report. Nevertheless, the differences in emission factors across various waste management
options are sufficiently large as to imply that GHG mitigation policies in the waste sector can
make a significant contribution to US emission reductions. A number of examples, using the
emission factors in this report, bear this out.
• At the firm level, targeted recycling programs can reduce GHGs. For example, a
commercial facility that shifts from a baseline practice of landfilling (in a landfill
with no gas collection system) to recycling 50 tons office paper and 2 tons of
aluminum cans can reduce GHG emissions by over 100 MTCE.
• At the community level, a city of 100,000 with average waste generation (4.3
Ib/day per capita) and recycling (27 percent), and baseline disposal in a landfill
15 Sustainable biogenic sources include paper and wood products from sustainably managed
forests; when these materials are burned or aerobically decomposed to GO,, the CO, emissions are not
counted. Our approach to measuring GHG emissions from biogenic sources is described in detail in
Chapter 1.
16 For details on the sensitivity analyses, see section 7.4 and Exhibits 7-7 and 7-8.
ES-15
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with no gas collection system, could increase the recycling rate to 40 percent —
for example, by implementing a pay-as-you-throw program — and reduce
emissions by about 10,000 MTCE per year. (Note that further growth in
recycling would be possible; some communities are already exceeding recycling
rates of 50 percent).
• A city of 1 million, disposing of 650,000 tons per year in a landfill without gas
collection, could reduce GHG emissions by 92,000 MTCE per year by managing
waste in a mass burn combustor unit.
• A town of 50,000 landfilling 30,000 tons per year could install a landfill gas
recovery system and reduce emissions by about 6,600 MTCE per year.
• At the national level, if the US attains the goal of a 35 percent recycling rate by
2005, emissions will be reduced by over 9 million MTCE per year compared to a
baseline where we maintain the current 27 percent recycling rate and use the
"national average" landfill for disposal.
ES.7 LIMITATIONS OF THE ANALYSIS
When conducting this analysis, we used a number of analytical approaches and
numerous data sources, each with its own limitations. In addition, we made and applied
assumptions throughout the analysis. Although these limitations would be troublesome if used in
the context of a regulatory framework, we believe that the results are sufficiently accurate to
support their use in voluntary programs. Some of the major limitations follow:
• The manufacturing GHG analysis is based on estimated industry averages for
energy usage, and in some cases the estimates are based on limited data.17 In
addition, we used values for the average GHG emissions per ton of material
produced, not the marginal emission rates per incremental ton produced. In some
cases, the marginal emission rates may be significantly different.
• The forest carbon sequestration analysis deals with a very complicated set of
interrelated ecological and economic processes. Although the models used
represent the state-of-the-art in forest resource planning, their geographic scope
is limited—because of the global market for forest products, the actual effects of
paper recycling would occur not only in the US but in Canada and other
countries. Other important limitations include: (1) the estimate does not include
changes in carbon storage in forest soils and forest floors, (2) the model assumes
that no forested lands will be converted to non-forest uses as a result of increased
paper recycling, and (3) we use a point estimate for forest carbon sequestration,
whereas the system of models predicts changing net sequestration over time.
• The composting analysis was limited by the lack of data on methane generation
and carbon sequestration resulting from composting; we relied on a theoretical
approach to estimate the values.
• The combustion analysis uses national average values for several parameters;
variability from site to site is not reflected in our estimate.
17 When EPA published this report as a draft working paper, the Agency specifically requested that
commenters provide data on raw material acquisition and manufacturing. Although several ccmmenters
agreed that updated information would be important, none provided such data.
ES-16
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• The landfill analysis (1) incorporates considerable uncertainty on methane
generation and carbon sequestration, due to limited data availability, and (2) uses
as a baseline landfill methane recovery levels projected for the year 2000.
Finally, through most of the report we express analytical inputs and outputs as point
estimates. We recognize that a rigorous treatment of uncertainty and variability would be useful,
but in most cases the information needed to treat these in statistical terms is not available. The
report includes some sensitivity analyses to illustrate the importance of selected parameters, and
expresses ranges for a few other factors such as GHG emissions from manufacturing. We
welcome readers to provide better information where it is available; perhaps with additional
information, future versions of this report will be able to shed more light on uncertainty and
variability. Meanwhile, we caution that the emission factors reported here should be evaluated
and applied with an appreciation for the limitations in the data and methods, as described at the
end of each chapter.
ES-17
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