United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-95/019 February 1995
4? EPA Project Summary
Estimate of Global Methane
Emissions from Landfills and
Open Dumps
Michiel R.J. Doom and Morton A. Barlaz
Methane (CH4) produced by the
anaerobic decomposition of waste bur-
ied in landfills and open dumps is a
significant contributor to global CH4
emissions, with estimates ranging from
10 to 70 teragrams per year (Tg/yr or
10" g/yr). Global anthropogenic sources
emit 360 Tg/yr, which suggests that
landfills may account for 3 to 19% of
the total. The report presents an em-
pirical model to estimate global CH4
emissions from landfills and open
dumps, based on data from landfill gas
(LFG) recovery projects, developed by
the U.S. Environmental Protection
Agency's (EPA's) Air and Energy Engi-
neering Research Laboratory (AEERL).
The AEERL CH4 estimates for 1990
range from 21 to 46 Tg/yr with a
mid-point of 33 Tg/yr.
Many developed countries are en-
couraging incentive programs or regu-
latory requirements for municipal solid
waste (MSW) landfills that could result
in a reduction of CH4 from landfills.
The U.S. is scheduled to promulgate
Clean Air Act regulations for MSW land-
fills by June 1995. This rule is esti-
mated to reduce CH4 emissions by 5 to
7 Tg/yr by the year 2000. Economical
growth in newly industrialized coun-
tries (e.g., Taiwan) and overall popula-
tion growth in developing countries are
expected to increase total yearly waste
generation. In developing countries,
better solid waste management meth-
ods may increase the amount of waste
that will be landfilled or dumped in the
future and thus increase CH4 emissions.
Substantial uncertainty in the global
estimates from this source results from
a lack of data characterizing (1)
country-specific waste generation, (2)
waste management practices, (3) CH4
potential of the waste in place, and (4)
CH4 that is emitted from waste piles
and open dumps.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
AEERL has used U.S. LFG recovery
data to develop an empirical model relat-
ing LFG flows to waste in place. LFG
recovery flow rates (m3/min) are converted
to CH4 emission rates (in g/min) by ac-
counting for the average LFG density, the
relative CH4 concentration in LFG, the av-
erage efficiency of the gas recovery sys-
tems, and the estimated oxidation of CH4
in the top soil cover of the landfill. CH4
emissions (Tg/yr) from landfills equal
= CF*R*X.
(1)
where CF is a conversion factor, R is the
emission factor, and X is the estimate of
waste in place (Tg/yr) decomposing under
anaerobic conditions. For sanitary land-
fills, which are considered to be completely
anaerobic, X is equal to total waste in
place. CH4 emissions are decreased by
the amount of CH4 that is currently recov-
ered or flared (YR). It is estimated that
worldwide there are about 270 sites in 20
countries where LFG is recovered.
Waste Generation
For most countries, data on X are not
available and have to be developed from
waste generation rates. The methodology
distinguishes between rural and urban
waste generation rates. To obtain X, the
Printed on Recycled Paper
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total annual waste generation rate M (Tg/
yr) is multiplied by the CH4 generation
time G (yr), which is the "lifetime" that a
batch of waste continues to produce CH4
(average 25 yr) in a landfill.
Per capita MSW generation rates range
from 1.7 to 1.9 kg/day for the U.S. and
Canada. Per capita MSW generation rates
in other developed countries are about
1.2 kg/day. For developing countries, rates
are about 0.8 kg/day for urban, and 0.3
kg/day for rural areas. MSW generation
rates were multiplied with population data
to obtain M.
Global Methodology
To adapt Equation (1) for other coun-
tries requires two modifications. The first
modification concerns the fact that waste
management practices in other countries
differ considerably from the U.S. practice
of sanitary landfilling. The second modifi-
cation addresses the relationship between
composition and CH4 potential of waste in
place. CH4 potential is defined as the maxi-
mum amount of CH4 that may be gener-
ated by a certain batch of waste.
In developed countries, not all waste
that is generated is actually landfilled. Parts
may be incinerated, composted, or re-
cycled. In developing countries, part of
the waste may be fed to animals or burned
within the household. Also, much of the
garbage is scavenged before it is col-
lected. Refuse may also be dumped in
rivers, swept out onto the streets, or bur-
ied. In addition, garbage is often burned
at the dump to reduce the volume. Finally,
open dumps are often scavenged again
by humans and animals. The methodol-
ogy described in the report accounts for
these practices by introducing a factor L
to express the amount of generated waste
that is eventually landfilled or dumped.
For U.S. landfills, which are considered
to be completely anaerobic, X is equal to
total waste in place. In other cases, for
instance in open dumps, not all waste
may be decomposing anaerobically. To
account for this, a country-specific factor
F is introduced to express the average
degree in which anaerobic decomposition
takes place within the dumps or landfills.
The emission factor used in this report
is based on field measurements of CH4
from U.S. waste. Compared to U.S. waste,
waste in other countries will probably have
a different composition and CH4 potential.
In the methodology, this difference is ac-
counted for by relating the country-specific
CH4 potential to the U.S. potential.
By adjusting for L, F, and the relative
CH4 potential, the equation to estimate
CH4 emissions from landfills and open
dumps for a certain country is
us
(2)
Global estimates are obtained by sum-
ming country-specific emissions. Estimates
of CH4 emissions from global landfills
range from 21 to 46 Tg/yr, with a 33 Tg/yr
midpoint.The U.S. is the biggest contribu-
tor, accounting for 39% of world emis-
sions.
Trends and Uncertainties
In the future, plans by developed coun-
tries to place less waste in landfills in
favor of recycling and incineration would
help to reduce landfill CH4. Also, controls
for LFG emissions are being considered
by these countries. The U.S. is scheduled
to promulgate Clean Air Act regulations
for municipal solid waste landfills by June
1995. This rule is estimated to decrease
CH4 emissions by 5 to 7 Tg/yr by the year
2000. Economical growth in newly indus-
trialized countries and overall population
growth in developing countries are ex-
pected to increase total yearly waste gen-
eration. Also, in developing countries, there
is a distinct intent to improve solid waste
management methods for sanitation rea-
sons. Better solid waste management
methods may increase the amount of
waste that will be landfilled or dumped in
the future and thus increase CH4 emis-
sions.
Substantial uncertainty in the global
estimates from this source results from
a lack of data characterizing (1)
country-specific waste generation, (2)
waste management practices, (3) CH4
potential of the waste in place, and (4)
CH4 that is emitted from waste piles and
open dumps.
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Michiel R. J. Doom is with E.H. Pechan and Associates, Inc., Durham, NC 27707.
Morton A. Barlaz is with N.C. State University, Raleigh, NC 27650.
Susan A. Thorneloe is the EPA Project Officer (see below).
The complete report, entitled "Estimate of Global Methane Emissions from Landfills
and Open Dumps," (Order No. PB95-177002; Cost: $19.50, subject to change)
will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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