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The Impact of Municipal Solid Waste Management on
Greenhouse Gas Emissions in the United States
Keith A. Weitz a , Susan A. Thorneloe b , Subba R. Nishtala a , Sherry Yarkosky a & Maria
Zannes c
a Center for Environmental Analysis, RTI , Research Triangle Park , North Carolina , USA
b Air Pollution Prevention and Control Division, Office of Research and Development , U.S.
Environmental Protection Agency , Research Triangle Park , North Carolina , USA
c Integrated Waste Services Association , Washington , DC , USA
Published online: 27 Dec 2011.
To cite this article: Keith A. Weitz , Susan A. Thorneloe , Subba R. Nishtala , Sherry Yarkosky & Maria Zannes (2002) The
Impact of Municipal Solid Waste Management on Greenhouse Gas Emissions in the United States, Journal of the Air & Waste
Management Association, 52:9, 1000-1011, DOI: 10.1080/10473289.2002.10470843
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Weitz et al.
TECHNICAL PAPER
ISSN 1047-3289 J. Air & Waste Manage. Assoc. 52:1000-1011
Copyright 2002 Air & Waste Management Association
The Impact of Municipal Solid Waste Management on
Greenhouse Gas Emissions in the United States
Keith A. Weitz
Center for Environmental Analysis, RTI, Research Triangle Park, North Carolina
Susan A. Thorneloe
Air Pollution Prevention and Control Division, Office of Research and Development, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina
Subba R. Nishtala, and Sherry Yarkosky
Center for Environmental Analysis, RTI, Research Triangle Park, North Carolina
Maria Zannes
Integrated Waste Services Association, Washington, DC
ABSTRACT
that these displace virgin raw materials and fossil fuel elec-
tricity production, respectively. Carbon sinks associated
with MSW management also were addressed. The results
indicate that the MSW management actions taken by U.S.
communities have significantly reduced potential GHG
emissions despite an almost 2-fold increase in waste gen-
eration. GHG emissions from MSW management were es-
timated to be 36 million metric tons carbon equivalents
(MMTCE) in 1974 and 8 MMTCE in 1997. If MSW were
being managed today as it was in 1974, GHG emissions
would be ~60 MMTCE.
Technological advancements, environmental regulations,
and emphasis on resource conservation and recovery have
greatly reduced the environmental impacts of municipal
solid waste (MSW) management, including emissions of
greenhouse gases (GHGs). This study was conducted using
a life-cycle methodology to track changes in GHG emis-
sions during the past 25 years from the management of
MSW in the United States. For the baseline year of 1974,
MSW management consisted of limited recycling, combus-
tion without energy recovery, and landfilling without gas
collection or control. This was compared with data for 1980,
1990, and 1997, accounting for changes in MSW quantity,
composition, management practices, and technology. Over
time, the United States has moved toward increased recy-
cling, composting, combustion (with energy recovery) and
landfilling with gas recovery, control, and utilization. These
changes were accounted for with historical data on MSW
composition, quantities, management practices, and tech-
nological changes. Included in the analysis were the ben-
efits of materials recycling and energy recovery to the extent
INTRODUCTION
Solid waste management deals with the way resources
are used as well as with end-of-life deposition of materi-
als in the waste stream.1 Often complex decisions are
made regarding ways to collect, recycle, transport, and
dispose of municipal solid waste (MSW) that affect cost
and environmental releases. Prior to 1970, sanitary land-
fills were very rare. Wastes were “dumped” and organic
materials in the dumps were burned to reduce volume.
Waste incinerators with no pollution controls were com-
mon.1 Today, solid waste management involves technolo-
gies that are more energy efficient and protective of
human health and the environment. These technologi-
cal changes and improvements are the result of decisions
made by local communities and can impact residents
directly. Selection of collection, transportation, recycling,
treatment, and disposal systems can determine the num-
ber of recycling bins needed, the day people must place
their garbage at the curb, the truck routes through resi-
dential streets, and the cost of waste services to house-
holds. Thus, MSW management can be a significant issue
for municipalities.
IMPLICATIONS
Technology advancements and the movement toward in-
tegrated strategies for MSW management have resulted
in reduced GHG emissions. GHG emissions from MSW
management would be 52 MMTCE higher today if old
strategies and technologies were still in use. Integrated
strategies involving recycling, composting, waste-to-en-
ergy combustion, and landfills with gas collection and
energy recovery play a significant role in reducing GHG
emissions by recovering materials and energy from the
MSW stream.
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Weitz et al.
MSW management is also an issue of global signifi-
cance. The MSW management decisions made by may-
ors, county executives, and city and county councils and
boards can impact the release of greenhouse gas (GHG)
emissions that contribute to global climate change. GHG
emissions can trap heat in the atmosphere and lead to
warming the planet and changing its weather. According
to the latest U.S. Environmental Protection Agency (EPA)
inventory of GHG emissions, the waste management sec-
tor represents ~4% of total U.S. anthropogenic GHG emis-
sions (i.e., 260 out of 6750 teragrams of CO2 equivalents).2
Landfills are the largest anthropogenic source of CH4 in
the United States and represented ~90% of GHGs from
the waste sector in 1999.2 Emissions of CH4 result from
the decomposition of biodegradable components in the
waste stream such as paper, food scraps, and yard trim-
mings. The potential for global climate change caused by
the release of GHGs is being debated both nationally and
internationally. Options for reducing GHG emissions are
being evaluated. MSW management presents potential
options for GHG reductions and has links to other sec-
tors (e.g., energy, industrial processes, forestry, and trans-
portation) with further GHG reduction opportunities.
This study was conducted for the U.S. Conference of
Mayors through funding provided by the Integrated Waste
Services Association. It examined the effect of local MSW
management decisions on GHG emissions during the past
25 years. The scope of the study included all activities that
play a role in MSW management, from the point at which
the waste is collected to its ultimate disposition. These
activities include MSW collection, transport, recycling,
composting, combustion (with and without energy recov-
ery), and landfilling (with and without gas collection and
energy recovery). The life-cycle environmental aspects of
fuel and electricity consumption were also included, as well
as the displacement of virgin raw materials through recy-
cling and the displacement of fossil fuel-based electrical
energy through energy recovery from MSW. The GHG
emissions studied in this analysis were CO2 and CH4. Other
GHG emissions such as perfluorocarbons (PFCs) and N2O
were not included, primarily because of limitations in avail-
able data. Carbon sinks associated with MSW management
were evaluated, and results were presented with and with-
out carbon sinks included.
study tracks the material and energy flows from cradle to
grave. Figure 1 provides an overview of the life-cycle flow
diagram of materials in MSW from cradle to grave that were
included in this study.5
The boundaries for this study include unit processes
associated with waste management, including production
and consumption of energy, extraction of raw materials,
transport, collection, recycling/composting, combustion,
and landfilling. The waste to be managed is dictated by
the quantity and composition generated in the United
States in the years studied. The net energy consumption
and environmental releases associated with managing MSW
are calculated, including offsets for (1) energy produced
from waste combustion and landfill gas utilization and (2)
energy and virgin resources that are conserved as a result
of recycling programs. The offsets and environmental re-
leases are specific to the different types of materials within
the waste stream, which includes the different types of alu-
minum, glass, paper, plastics, and steel in MSW.6
The technical analysis for this study was conducted
by RTI International under the direction of EPA’s Office
of Research and Development (ORD) using data and a
computer-based decision support tool (referred to hereaf-
ter as the MSW DST) developed through a cooperative
agreement between EPA/ORD and RTI.7,8 Representatives
from EPA, RTI, Integrated Waste Services Association, U.S.
Conference of Mayors, Solid Waste Association of North
America, Environmental Industry Associations, Waste
Management Inc., and ICF Consulting worked coopera-
tively to review this analysis.
METHODOLOGY
To calculate GHG emissions from MSW management,
data were collected on the breakdown of MSW by ma-
terial for 1974, 1980, 1990, and 1997. The most recent
year for which comprehensive information is available
is 1997.9 The oldest available data for MSW manage-
ment practices were from 1974.10 A review of techno-
logical changes and management practices was
conducted. Since 1974, MSW management in the
United States is much more complex than simply haul-
ing the waste to a “dump.” Advances in technology, in
addition to federal and state regulations, have resulted
in substantial investments in residential and nonresi-
dential infrastructure for collecting, transporting, and
processing of recycling and composting, and for dis-
posal techniques.1 In a 1995 study of U.S. communi-
ties, substantial diversity in system complexity was
found, reflecting differences in geographical locations,
types and quantities of solid waste managed, operational
and ownership structures, energy use, and environmen-
tal safety regulations and guidelines.11 This is quite dif-
ferent from how waste was being managed in the 1970s.
The life cycle of waste is often referred to as a journey
from cradle to grave (i.e., from when an item is put on the
curb or placed in a dumpster to when value is restored by
creating usable material or energy, or the waste is trans-
formed into emissions to water or air or into inert material
placed in a landfill).3 Methodologies that provide for a more
holistic approach toward evaluating the operations within
waste management systems that are interconnected began
to be introduced in 1995.4 The methodology used in this
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Weitz et al.
Figure 1. Diagram of material and energy life-cycle flows and the associated GHG sources and sinks.5
The following is a description of four U.S. communities
using information from the report published in 1995 to
illustrate the diversity and complexity that exists.11
facility (MRF) that processes recyclables, and a co-
composting facility that processes sewage sludge mixed with
source-separated yard waste. About 19% of the MSW is re-
covered for recycling programs. Compost is processed in
an enclosed building using an aerated, agitated bay tech-
nology. Only residual waste and ash are sent to landfills.13
In 1992, Scottsdale, AZ, system components included
collection and transport of curbside MSW and on-call col-
lection of corrugated moving boxes. There were also drop-
off sites for MSW and recyclables. Less than 1% of the
MSW was recovered for recycling. More than 92% of the
MSW was transported to three unlined landfills.14
In Seattle, WA, the system components included col-
lection and transport of curbside MSW, yard waste, and
recyclables. There were also two transfer stations, two
MRFs, and a source-separated yard waste compost facil-
ity. The compost facility is in a rural area and is an open-
air facility. It uses large windrow piles that are turned and
aerated by a windrow turner to process the compost. Re-
sidual waste is hauled by rail to a lined landfill. At the
time of the study, 13% of yard waste was composted, and
15% of MSW was recycled.15 Because of the closing of two
city-operated landfills in the late 1980s, the city decided
to pursue an aggressive waste reduction program and set
a recycling goal of 60% of the waste stream by 1998. In
1996, Seattle was approaching this goal, diverting 49% of
Complexity of MSW Management
Systems in the United States
The Minnesota Waste Management Act was passed in 1980.
Since then, substantial changes have occurred throughout
the United States. In Minnesota during the study, system
components included collection and transport of curbside/
alley residential and commercial waste, recyclables, yard
waste collection services, drop-off sites, and transfer sta-
tions. There is also a mass-burn MSW combustion facility
(with energy recovery), three refuse-derived fuel (RDF) waste
processing facilities, and a private processing facility for
recyclables. Of the MSW being processed, 15% is recycled
and 11% (i.e., yard waste) is composted. Regional and out-
of-state landfills are used for the disposal of residues, non-
processible waste, and ash.12
In Palm Beach County, FL, system components include
collection and transport of curbside MSW, recyclables, and
yard waste. There are also drop-off sites and transfer stations.
The system also includes four transfer stations, MSW com-
bustion (with energy recovery), an RDF processing
facility, a ferrous processing facility that produces a market-
able product from recovered ferrous, a materials recovery
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Weitz et al.
its residential waste stream, 48% of its commercial waste
stream, and 18% of materials delivered to drop-off sites.
The recyclable materials were collected and processed at
two private facilities using conveyors, trommel and disc
screens, magnetic separation, air classification, balers, and
hand-sorting to separate materials.16
for avoiding GHG emissions and offsetting fossil fuel con-
sumption. Table 1 provides a list of GHG emission sources
and sinks associated with the waste management. All these
emission sources and sinks were accounted for in each of
the years that were included in this study. Although waste
management strategies and technologies changed from
1974 to 1997, other aspects, such as transportation dis-
tances, were kept constant because their overall contribu-
tion to the results were minimal.26 Data were not available
across all waste management practices for PFCs and N2O.
Consequently, they were not included in the study. As
additional data become available, they can be included
in future analyses.
Across the United States, technological advancements
in collection, transport, recycling/composting, combustion,
and landfilling are helping to minimize potential impacts
to human health and the environment. For example, fed-
eral and state requirements are in place under the Resource
Conservation and Recovery Act of 1976 and the Clean Air
Act. For the baseline year of this study, waste was typically
hauled to dumps with nuisances associated with odor, air-
born litter, occurrence of disease vectors such as rats, mice,
and flies, as well the generation of landfill gas emissions
and leachate resulting from the decomposition of biode-
gradable waste and rainwater filtering through the landfilled
waste.17,18 Today’s landfills are modern “sanitary landfills
in response to state and federal requirements for liners,
leachate collection and treatment, and prevention of land-
fill gas explosions.”19,20 In 1996, New Source Performance
Standards and Emission Guidelines were promulgated re-
quiring that landfill gas be collected and controlled at
large landfills (>2.5 million tons of waste).21 The first land-
fill gas-to-energy recovery project began operating in
1981.22 Now there are 300 landfill gas-to-energy projects
producing electricity or steam.23
The methodology used for this study is intended to
illustrate GHG emissions and reduction potentials for the
integrated waste management system (i.e., all aspects from
collection, transportation, remanufacturing into a new
product, or disposal are accounted for). This study was not
designed to compare GHG reduction potential between
specific MSW management technologies (e.g., recycling vs.
combustion). The MSW DST was used to calculate the net
GHG emissions resulting from waste collection, transport,
recycling, composting, combustion, and land disposal
option (i.e., offsets for displacement of fossil fuel). Both
direct GHG emissions from each waste management activ-
ity and the GHG emissions associated with the production
and consumption of fuels were included.
For some of the lower quantity materials in MSW,
data from the MSW DST were not available. This repre-
sented 1.5% of the total waste generated in 1974 and 4%
of that in 1997. For these waste streams, data were
obtained from EPA’s Office of Solid Waste. These items
include durable goods, wood waste, rubber tires, textiles,
and lead-acid batteries.
MSW combustion has also gone through substantial
changes. In the 1970s, MSW was directly combusted with-
out energy recovery and with little or no pollution con-
trol. Currently, there are 102 facilities in the United States
that combust waste to generate steam or electricity. In these
communities, the average recycling rate is 33%, which is
5% greater than the national average.24 These facilities also
have heat recovery, electricity production, and the highest
levels of pollution control. Results from a recent EPA in-
ventory of these facilities has shown that emissions are well
below emission limits established by the Clean Air Act.25
Recycling also has greatly increased, growing from
8% in the 1970s to 27% in 1997. Many communities
now have state-of-the art material recovery facilities, and
there is a dramatic increase in the amounts of food and
yard waste being composted. Technological innovations
have occurred, making these operations more efficient
and cost effective.15
The energy consumed and environmental releases as-
sociated with production of new products, as well as those
saved by using recycled instead of virgin materials, were in-
cluded in the analysis. GHG emission savings also were cal-
culated for MSW management strategies (namely, MSW
combustion and landfill) where energy was recovered. In
calculating the GHG emission savings associated with en-
ergy recovery, the “saved” energy was assumed to result from
offsetting the national electric grid. For every kilowatt-hour
of electricity produced from MSW, the analysis assumed that
a kilowatt-hour of electricity produced from fossil fuels was
not generated. Wherever energy is consumed (or produced),
the analysis includes environmental releases (or savings)
associated with both the use and production (e.g., the pro-
duction of a gallon of diesel fuel) of that energy.
The changes in technology and management prac-
tices were taken into account for the different years in-
cluded in the study. The percentages of MSW being
recycled (which includes composting), landfilled, and
combusted are provided in Figure 2 for each of the years
included in this study. Each of these contributes to the
production of GHG emissions, as well as to the potential
To complete this study, information about MSW gen-
eration and composition was needed for 1974, 1980, 1990,
and 1997. We used three primary data sources to calculate
MSW generation and composition: (1) EPA’s Municipal
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Weitz et al.
Figure 2. Changes in the management of MSW in the United States from 1974 to 1997. 9,10
Solid Waste Characterization Report for 1998 (providing
information about 1980, 1990, and 1997 waste trends,
composition, and generation);9 (2) unpublished waste
characterization data for 1974 from Franklin Associates;10
and (3) U.S. Bureau of the Census historical housing data.27
EPA and Franklin Associates waste characterization stud-
ies include data for waste generation and composition and
MSW management practices in the United States. The
amount of MSW generated in the United States for each
of the study years is shown in Table 2. Waste composition
data are shown in Table 3, and waste management data
are shown in Table 4.
location in the commercial sector). The composition and
quantities of materials recycled and composted were set at
the levels of recycling reported by EPA’s and Franklin Asso-
ciates’ national data sets. Recycling and composting rates
were based on EPA data.9 The composition of materials that
are recycled and composted is presented in Table 5.
Using the previous data, GHG emissions were calcu-
lated for the years 1974, 1980, 1990, and 1997. Figure 2
illustrates the changes to solid waste management for each
of these years. In 1974, waste management primarily in-
volved the collection and landfilling of MSW. About 8%
of waste was recycled as commingled material and 21%
of waste was combusted (without energy recovery). The
remaining 71% of waste was landfilled without landfill
gas control. During the next 25 years, recycling steadily
increased from 8% in 1974 to 10% in 1980, 16% in 1990,
U.S. Census data27 were used to estimate the number
of residential, multifamily, and commercial waste genera-
tors. This information was used within the MSW DST to
generate waste generation rates (in lb/person/day, or lb/
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Weitz et al.
Table 1. Sources and sinks for GHG emissions from MSW management-related technologies included in the analysis.
cycle was being analyzed.
However, the MSW DST
was developed to include
an offline calculator for
estimating carbon storage
potentials resulting from
forests, soils, and landfills.
Users can decide whether
to calculate and incorpo-
rate the carbon storage po-
tentials into their analysis.
For this study, results with
and without carbon stor-
age included are provided.
The carbon storage val-
Waste Management Activity
Collection (recyclables and mixed waste)
Material recovery facilities
GHG Emissions (CH4 and CO2) Sources and Sinks
Combustion of diesel in collection vehicles
Production of diesel and electricity (used in garage)
Combustion of diesel used in rolling stock (front-end loaders, etc.)
Production of diesel and electricity (used in building and for equipment)
Combustion of diesel used in rolling stock
Production of diesel and electricity (used for equipment)
Combustion of waste
Yard waste composting facility
Combustion (also referred to as waste to energy)
Landfill
Offsets from electricity produced
Decomposition of waste
Combustion of diesel used in rolling stock
Production of diesel
Offsets from electricity or steam produced
Combustion of diesel used in vehicles
ues used in this study and
included in the MSW DST
calculator are from EPA’s
Office of Solid Waste in a
report that was released in
19985 to support its vol-
Transportation
Production of diesel
Reprocessing of recyclables
Offsets (net gains or decreases) from reprocessing recyclables
recovered; offsets include energy- and process-related data
and 27% by 1997. By 1980, waste combustion without
energy recovery declined and was replaced by waste-to-
energy plants. Data indicate that by 1997, 17% of the MSW
generated in the United States was used to produce elec-
tricity at 102 waste-to-energy facilities nationwide. Also
in 1997, 56% of the waste that was landfilled was going to
~1200 sites with liners, leachate collection, and control.
Some of these sites, primarily the larger ones, also have
landfill gas control. All of these considerations were taken
into account in the calculations.
untary partnership program on climate change and
MSW management. This methodology tracks carbon
storage related to waste processes and tracks carbon as-
sociated with fossil fuel and nonenergy GHGs such as
PFCs and N2O. The principal carbon storage mecha-
nisms addressed are changes in forest carbon stocks re-
lated to paper and wood recycling, long-term storage
of carbon in landfills, and accumulation of carbon in
soils resulting from compost application. Carbon stor-
age from combustion ash residue also was studied and
was estimated to be negligible. Although carbon stor-
age in forests, soils, and landfills clearly has a strong
influence on net GHG emissions, the exact accounting
methods that should be used to quantify them are still
a matter of debate, because many scientific and policy
questions remain to be resolved. However, EPA currently
includes estimates of carbon storage from landfills and
forests in its national GHG inventory.1
Role of Carbon Sequestration and Storage
When CO2 is removed from the atmosphere by photo-
synthesis or other processes and stored in sinks (like for-
ests or soil), it is sequestered. One of the more controversial
issues with accounting for GHG emissions from MSW
management is associated with whether carbon sinks
should be considered. There is no consensus on a meth-
odology for estimating carbon storage in forests, soils, and
landfills. During the series of peer reviews conducted on
the methodology developed for the MSW DST, the rec-
ommendation from the reviewers was that carbon seques-
tration should not be considered unless a full product life
To help illustrate the difference in estimates of GHG
emissions when carbon storage is taken into account,
EPA’s Office of Solid Waste and ICF Consulting provided
data and information using the EPA WARM model28 for
making the comparisons. Table 6 shows the potential
carbon storage for the years that were evaluated for this
study. The negative values in the table indicate that the
storage is, in effect, a negative emission. In scenarios
where waste is managed according to 1974 technology,
substantial carbon storage is associated with landfills. In
the 1990s, the balance shifts—the large volume of paper
recycling results in substantial benefits in the form of
forest carbon storage, and there are also some soil car-
bon benefits from composting.
Table 2. Total MSW generated in the United States for each study year (metric tons).9,10
Year
Waste Generated
1974
1980
1990
1997
116,000,000
137,000,000
186,000,000
197,000,000
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Weitz et al.
Table 3. Waste composition.9,10
Composition (%)a
1974
Residential
1980
Residential
1990
Residential
1997
Residential
Waste Category
Commercial
Commercial
Commercial
Commercial
Yard trimmings, leavesb
Yard trimmings, grassb
Yard trimmings, branchesb
Newsprint
13
13
6.7
13
6.6
13
5.4
11
11
6.7
10
6.6
9.6
2.0
1.4
0.3
0.7
1.6
2.1
0.4
1.2
0.3
1.8
5.4
8.0
2.6
1.5
0.2
0.8
3.1
2.7
0.6
1.3
0.5
2.1
12
2.0
19
2.9
27
2.5
27
1.8
29
Corrugated cardboard
Office paper
2.2
1.1
1.9
1.1
3.0
5.3
5.9
0.3
5.7
0.2
Phone books
Books
3.0
2.9
Magazines
3rd-class mail
1.6
1.8
HDPE—translucentc
HDPE—pigmentedc
PETd
0.2
1.0
0.2
2.6
2.2
0.1
2.0
0.1
0.9
0.2
0.7
Steel cans
1.8
0.3
0.5
5.2
Ferrous metal—other
Aluminum—food cans
Aluminum—other cans
Aluminum—foil and closures
Glass—cleare
Glass—browne
Glass—greene
0.2
0
0.8
0.4
0.4
1.0
0.3
0.4
1.1
0.3
0.4
0.6
9.4
6.0
1.7
10
1.9
1.2
0.3
6.8
4.3
1.2
16
2.5
1.6
0.4
4.5
2.9
0.8
16
1.5
0.9
0.3
4.1
2.6
0.7
20
1.1
0.7
0.2
Paper—nonrecyclable
Food waste
11
7.0
8.8
9.2
Other organic materials
Plastic—nonrecyclable
Metals—nonrecyclable
Miscellaneous
27
41
40
17
43
16
40
18
1.8
14
3.1
14
4.5
13
0.3
aNumbers may not add up to 100% because of rounding; bYard waste split between leaves, grass, and branches was assumed to be 35, 35, and 30%, respectively; cHDPE is high-
density polyethylene; dPET is polyethylene terephthalate; eGlass composition split between clear, brown, and green was assumed to be 55, 35, and 10%, respectively.
RESULTS
integrated MSW management technologies employed in
each study year. The other pathway represents what GHG
emissions would be if the same 1974 technologies and
MSW management practices were used in all study years
(i.e., 1980, 1990, and 1997). As illustrated in
Figure 3 illustrates the overall trend in GHG emissions
from 1974 to 1997. Two technology pathways are shown.
One pathway represents GHG emissions from the actual
Table 4. Annual waste input to management options (metric tons).9,10
this figure, by adopting new technologies and
MSW management practices, GHG emissions
1974
1980
1990
Today
have decreased from 1974 to 1997, despite an
almost 2-fold increase in the quantity of waste
generated. Net GHG emissions in 1997 were
Collection of Yard Waste
Collection of Recyclables
Collection of Mixed Waste
0
0
3,800,000
10,400,000
6,700,000
10,700,000
20,900,000
35,300,000
~8 million MMTCE versus 36 MMTCE in 1974.
108,000,000 124,000,000 157,000,000 144,000,000
Recovery of Recyclables in MRFa 8,400,000
If the same technology and MSW management
practices were used today as were used in 1974,
net GHG emissions would be ~60 MMTCE.
Thus, it could be concluded that the employ-
ment of new MSW management technologies
currently are saving on the order of 52 MMTCE
per year. The following sections discuss the net
13,100,000
0
25,900,000
3,800,000
28,800,000
43,300,000
10,400,000
32,900,000
Composting (yard waste)
Combustion
0
23,900,000
83,600,000
62,500
12,400,000
Landfill of Mixed Waste
Landfill of Combustion Ash
112,000,000 128,000,000 111,000,000
41,700 70,500 89,200
aMRF is mixed recovery facility.
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Weitz et al.
Table 5. Recovery rates of materials.9,10
Recovery of Materials (%)a
1980
Residential
1974
Residential
1990
Residential
1997
Waste Category
Commercial
Commercial
Commercial
Residential
Commercial
Yard trimmings, leaves
Yard trimmings, grass
Yard trimmings, branches
Newsprint
0.0
0.0
0.0
31
13
13
13
44
5.5
1.1
0.0
28
16
46
46
46
29
3.1
0.9
1.4
81
14
5.2
41
29
7.2
53
64
11
74
67
19
Corrugated cardboard
Office paper
4.3
0.9
7.6
2.0
35
Phone books
8.2
Books
13
10
78
48
Magazines
3rd-class mail
7.5
28
HDPE—translucentb
HDPE—pigmentedb
PETc
3.8
1.4
37
25
31
9.7
50
64
13
58
7.4
24
23
54
4.3
5.6
1.3
35
1.9
5.6
16
22
22
50
Steel cans
4.2
0.5
27
2.1
0.4
Ferrous metal—other
Aluminum cans
Aluminum—foil and closures
Glass—clear
5.7
64
5.4
22
28
56
50
0
2.8
2.8
2.8
0.9
0.6
0.2
5.2
5.2
5.2
5.9
5.9
5.9
24
24
24
28
26
60
Glass—brown
22
Glass—green
22
aRecovery of materials is defined as the percentage of a material generated that is recycled. Where appropriate, materials that were recycled based on EPA data were combined into a
similar waste category for which reprocessing data were available. For example, 3rd-class mail and phone books recycled in 1997 were combined into the Books category. This
assumption makes some recovery numbers appear high; bHDPE is high-density polyethylene; cPET is polyethylene terephthalate.
contributions of GHGs from recycling and composting,
waste-to-energy combustion, landfills, and collection and
transportation practices. In addition, the effects of car-
bon storage on the net total GHG emissions are discussed.
disposal of materials from landfills that produce CH4 and
other GHGs. As shown in Figures 2 and 4, increasing re-
cycling and composting from ~8 million metric tons, or
8%, in 1974, to more than 53 million metric tons, or 27%,
in 1997, currently is avoiding the release of more than
3.2 MMTCE annually. These results include GHG emis-
sions from materials collection, separation, treatment
(in the case of composting), and transportation to a
remanufacturing facility. For recycled materials, GHG
Recycling and Composting
Recycling contributes to the reduction of GHG emissions
by displacing virgin raw materials and thereby avoiding
environmental releases associated with raw materials ex-
traction and materials production. In addition, recycling
and composting avoids GHG emissions by diverting the
Table 6. Carbon storage potentials for waste management strategies (MMTCE/yr).
Recycling
Scenario
(includes compost)
Landfill
Total
1974
–5.5
–8.6
–6.7
–14.9
–8.9
–26.4
–9.5
–12.8
–17.1
–15.4
–19.2
–20.7
–14.8
–21.0
–18.3
–25.6
–22.1
–34.2
–29.6
–41.2
–30.6
1980
1980 with 1974 technology
1990
1990 with 1974 technology
Today
Today with 1974 technology
Figure 3. Comparison of net GHG emissions for MSW management
reflecting technological changes, landfill diversion, and source reduction.
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Weitz et al.
Figure 4. Comparison of net GHG emissions for recycling and
composting. Avoided emissions reflect offsets from resource
conservation.
Figure 5. Comparison of net GHG emissions for MSW combustion.
Avoided emissions reflect offsets for fossil-fuel conservation from energy
that is produced.
emissions avoided by displacing virgin raw materials pro-
duction are netted out of the results. Additional emissions
also are avoided as the result of diversion from landfills
and from source reduction.
employed. The GHG emissions from combustion facili-
ties were based on emission test results provided to EPA
and state environmental agencies.29
Waste combustion is similar to recycling in that it
can reduce GHG emissions in two ways. First, combus-
tion diverts MSW from landfills where it would other-
wise produce CH4 as it decomposes. Second, the electrical
energy resulting from waste combustion displaces elec-
tricity generated by fossil fuel-fired power generators (and
associated GHG emissions). Figures 4 and 5 both reflect
the net decrease in emissions that are attributed to dis-
placement of virgin resources and fossil fuel. They do not
reflect added reductions from CH4 emissions that would
be avoided if waste were landfilled. If the avoided GHG
emissions were included in Figure 5, an additional 6
MMTCE would be reduced, increasing the total avoided
emissions from 5.5 to 11 MMTCE. If the MSW had been
landfilled, 33 million metric tons would have been re-
leased. The assumptions for this calculation are presented
in Table 7. Half of the MSW being landfilled is located at
sites with landfill gas control. Of these sites, half of those
with gas control utilize the landfill CH4 to produce steam
or electricity using reciprocating engines, boilers, and tur-
bines. Offsets for this produced energy were included in
the calculations. The total emissions were calculated to
ensure that a comparable basis was used in calculating
the avoided emissions. For combustion, emissions are re-
leased immediately. For landfills, the GHG emissions are
released over a long period of time, and not all of the
potential carbon is re-released. GHG emissions over a
100-year period were used for this study.
Combustion
For nearly 100 years, the United States has used com-
bustion as a means of waste disposal. Similar to landfill
technology of 25 years ago, the benefit of early combus-
tion technology was solely its disposal ability, as well as
its ability to destroy pathogens in waste. Energy recov-
ery through the combustion of waste was not consid-
ered seriously in the United States until the 1970s. At
that time, waste combustion technology developed from
a realization that waste had an inherent energy content
and could be harnessed to generate electricity. For the
past 20 years, combustion technology has grown to in-
clude an added benefit of energy recovery. Combustion
facilities have been successful in recovering materials
from the waste stream that can be recycled and recover-
ing energy from the residual waste to generate electric-
ity. All MSW combustion facilities in the United States
include recycling programs and energy production. Elec-
tricity generated from waste combustion has become so
reliable that the power is “base load” for utilities that
buy it, thereby allowing those utilities to avoid construc-
tion of new power plants or the purchase of fossil fuel-
generated electricity.
In 1974, ~24 million metric tons of MSW, repre-
senting ~21% of U.S. MSW, was managed in combus-
tion units without energy recovery. As shown in Figure
5, this technology was a net generator of GHG emis-
sions. By 1997, ~33 million metric tons of MSW, repre-
senting ~17% of U.S. MSW, was managed by MSW
combustion. This resulted in avoiding the release of ~5.5
MMTCE of GHG emissions annually, as compared to
GHG emissions if 1974 combustion technology was still
Landfills
In 1974, 108 million metric tons of MSW and combus-
tion ash were landfilled in the United States. In 1997, ~129
million metric tons of MSW and combustion ash were
landfilled, representing 56% of the MSW generated. As of
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Volume 52 September 2002

Weitz et al.
Table 7. Key landfill design and operation assumptions.
the distribution of energy recovery projects
(internal combustion engines, direct gas use,
gas turbines, etc.).23 Specific assumptions for
landfill gas parameters in each study year are
included in Table 7. These assumptions were
verified through communication with na-
tional experts. The GHG emissions associated
with fossil fuel-based electrical energy that was
displaced by the use of landfill gas was also
included in the calculations using the national
electrical energy grid mix.
Study Year
Parameter (%)
1974
1980
1990
1997
Waste managed in landfills with gas control
Landfill gas collection efficiency
CH4 oxidation rate
Controlled landfill gas utilized for
energy recovery projects using boilers,
reciprocating engines, and turbines
0
0
10
75
20
30
75
20
50
75
20
20
0
0
31
50
The results, as illustrated in Figure 7, indi-
cate that modern landfills in 1997 avoided the
2000, there were 2526 MSW landfills in the United
States.30 Landfills with gas collection systems reduce the
release of GHG emissions associated with the decom-
position of waste. Figure 6 illustrates the landfill gas-
generation rate over a 100-year period. Because GHG
emissions are reported for a specific time period, the
cumulative CH4 yield, as opposed to an annual emis-
sion rate, is needed to account for the total emissions
for the management (i.e., landfilling) of the MSW for
each year of the study. Energy can be recovered from
the utilization of the CH4 in landfill gas (which is typi-
cally ~50% of the landfill gas) to produce energy. Off-
sets for fossil fuel conservation were included in the
analysis, as was done for recycling and combustion.
Because of diversion of waste from landfills, the growth
of landfill gas-to-energy projects from 0 in 1974 to
nearly 300 in 1997,23 Clean Air Act requirements, and
improvements in landfill design and management,
there has been a substantial reduction of GHG emis-
sions associated with MSW landfills.
release of 44 MMTCE of GHG emissions annually. This level
of avoided GHG emissions was achieved through the use
of gas collection and control systems, as well as the diver-
sion of MSW from landfills by using recycling, composting,
and combustion technologies. The key factors in determin-
ing GHG emissions produced from landfills are the amount
of waste managed, level of gas collection and control, ef-
fectiveness and timing of the control, and level and type
of energy recovery. Gas that would be oxidized and not
emitted as CH4 was also accounted for. The gas collection
efficiency that was used was obtained from EPA’s guidance
on estimating landfill gas emissions and is considered en-
vironmentally conservative.31
Collection and Transportation
Collection and transportation of MSW and recyclables
accounted for ~0.5 and 1 MMTCE in 1974 and 1997, re-
spectively. More GHG emissions were emitted in 1997
from collection and transportation because of the dou-
bling of the amount of MSW generated and collected since
1974. In addition to increases in GHG emissions from
collection and transportation, increases in other local
pollutants (such as SOx, NOx, CO, O3, and particulate)
should also be considered, particularly in regions that are
For the baseline year of 1974, there was no gas con-
trol or energy recovery. For 1997, using recent data, GHG
emissions were calculated based on 50% of MSW being
landfilled at sites with landfill gas collection and con-
trol.23 Of this 50%, half of the gas was flared and half
was used for energy recovery using recent statistics of
Figure 7. Comparison of net GHG emission reductions from landfills
caused by diversion of waste from landfills, increased landfill gas control,
and energy recovery of landfill CH4.
Figure 6. Landfill gas-generation rate during a 100-year period.32,33
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Journal of the Air & Waste Management Association 1009

Weitz et al.
Table 8. Non-GHG pollutant releases from waste collection and transportation (lb/yr).
•
•
Increasing recycling and composting efforts from
8 to 27% resulted in savings of 4 MMTCE from
avoiding use of virgin materials.
Producing electricity in waste combustion facilities
avoids 5 MMTCE that otherwise would have been
produced by fossil fuel electrical energy generation
and avoids 6 MMTCE of GHG emissions that would
be produced if the MSW were landfilled.
Pollutant
Scenario
SOx
NOx
CO
Particulate
1974
166,000
167,000
167,000
229,000
221,000
272,000
245,000
1,530,000
1,580,000
1,580,000
2,150,000
2,100,000
2,490,000
2,310,000
273,000
287,000
285,000
403,000
378,000
488,000
414,000
23,900
25,300
24,900
36,300
32,900
45,600
36,200
1980
1980 with 1974 technology
1990
•
•
There has been an increasing diversion of MSW
from landfills by using recycling, composting,
and waste combustion.
1990 with 1974 technology
1997
1997 using 1974 technology
Increasing landfill gas collection and energy re-
covery technology avoids 32 MMTCE that would
otherwise have been produced by older landfills
(without landfill gas control), by displacing fos-
sil fuel consumption for that portion of sites uti-
lizing landfill CH4 (rather than flaring the gas),
and through diversion to other technologies and
source reduction.
Table 9. Net GHG emissions, including the effects of carbon sequestration for waste management
strategies (MMTCE/yr).
Estimated Amount of
Carbon Sequestered
(from Table 6)
Estimated GHG
Emissions
Total Net GHG
Emissions
Scenario
This study illustrates that there has been a positive
1974
–18.3
–25.6
–22.1
–34.2
–29.6
–41.2
36.2
16.7
38.0
15.6
54.2
8.0
17.9
–8.9
15.9
impact on GHG emissions as a result of technology
advancements in managing MSW and more inte-
grated management strategies. Although there has
been a 60% increase in MSW since 1974, more than
52 MMTCE of GHG emissions per year are being
avoided based on actions taken in U.S. communi-
ties. There are additional opportunities for decreases
in GHG emissions as well as improvement in other
1980
1980 with 1974 technology
1990
–18.6
24.6
1990 with 1974 technology
1997
–33.2
29.9
1997 using 1974 technology
–30.6
60.5
environmental cobenefits through improved materials and
energy recovery from MSW management. From this study,
it can be concluded that the greatest reductions in GHG
emissions during the past 25 years have come from tech-
nology advancements to recover energy and recycle mate-
rials. The large reductions in GHG emissions from energy
recovery and recycling result from displacing the need to
produce energy from fossil sources and to produce new
raw materials from virgin sources.
classified as nonattainment areas with respect to the Na-
tional Ambient Air Quality Standards. Table 8 includes
estimates of other non-GHG pollutants associated with
waste collection and transportation.
Carbon Sequestration and Storage
The magnitude of carbon storage relative to the magni-
tude of emissions is shown in Table 9. When the consid-
eration of carbon storage is included in the calculations,
it dramatically offsets all of the energy and landfill emis-
sions. If carbon sequestration is considered in this analy-
sis, net GHG emissions avoided remain a factor of ~6.
Overall, the basic findings remain the same: improvements
in management have resulted in dramatically reduced net
GHG emissions from the waste sector.
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About the Authors
Keith Weitz (corresponding author) and Sherry Yarkosky are
environmental scientists and Subba Nishtala is a civil engi-
neer at the Center for Environmental Analysis at the Re-
search Triangle Institute, an independent organization dedi-
cated to conducting innovative, multidisciplinary research
that improves the human condition. Weitz led the develop-
ment of the MSW decision support tool used to estimate
GHG emissions in this paper. He may be reached at phone:
(919) 541-6973; e-mail: kaw@rti.org. Additional information
about the MSW decision support tool is available through
the project Web site.9 This World Wide Web site will be up-
dated as the final project documents are completed and
the details for the release of the decision support tool are
finalized. Susan Thorneloe is a chemical engineer at the U.S.
Environmental Protection Agency. She has worked for more
than 20 years in the characterization of air emissions and
control technologies for waste management sources, in-
cluding landfills, wastewater, septic sewage, and agricul-
tural waste. Maria Zannes is president of the Integrated
Waste Services Association, a national trade group that pro-
motes an integrated approach to solid waste management,
including reuse, recycling, waste-to-energy, and landfilling
of trash in an environmentally sound manner.
Volume 52 September 2002
Journal of the Air & Waste Management Association 1011