United States Air and Energy Engineering

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

Research and Development EPA/600/SR-95/019 February 1995

E AP

Estimate of Global Methane

Emissions from Landfills and

Open Dumps

Project Summary

Methane (CH4) produced by the

anaerobic decomposition of waste buried 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

1012 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 empirical 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 Engineering 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 encouraging incentive programs or regulatory 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 landfills by June 1995. This rule is estimated to reduce CH4 emissions by 5 to

7 Tg/yr by the year 2000. Economical

growth in newly industrialized countries (e.g., Taiwan) and overall population growth in developing countries are

expected to increase total yearly waste

generation. In developing countries,

better solid waste management methods 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 documented in a separate report of the same

title (see Project Report ordering information at back).

Introduction

AEERL has used U.S. LFG recovery

data to develop an empirical model relating LFG flows to waste in place. LFG

recovery flow rates (m3

/min) are converted

to CH4 emission rates (in g/min) by accounting for the average LFG density, the

relative CH4 concentration in LFG, the average efficiency of the gas recovery systems, and the estimated oxidation of CH4

in the top soil cover of the landfill. CH4

emissions (Tg/yr) from landfills equal

y 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 landfills, 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 recovered 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

Michiel R.J. Doorn and Morton A. Barlaz
2

rivers, swept out onto the streets, or buried. 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 methodology 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 accounted 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

Y LF P

P

M Y

US

=∗∗ ∗ ∗ ∗ − R

− 47 10 3

(2)

Global estimates are obtained by summing 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 contributor, accounting for 39% of world emissions.

Trends and Uncertainties

In the future, plans by developed countries 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 industrialized countries and overall population

growth in developing countries are expected to increase total yearly waste generation. Also, in developing countries, there

is a distinct intent to improve solid waste

management methods for sanitation reasons. Better solid waste management

methods 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.

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 countries 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 modification addresses the relationship between

composition and CH4 potential of waste in

place. CH4 potential is defined as the maximum amount of CH4 that may be generated by a certain batch of waste.

In developed countries, not all waste

that is generated is actually landfilled. Parts

may be incinerated, composted, or recycled. 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 collected. Refuse may also be dumped in
3

Michiel R.J. Doorn 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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