Methane generation in landfills

Abstract

Methane gas is a by-product of landfilling municipal solid wastes (MSW). Most of the global MSW is dumped in non-regulated landfills and the generated methane is emitted to the atmosphere. Some of the modern regulated landfills attempt to capture and utilize landfill biogas, a renewable energy source, to generate electricity or heat. As of 2001, there were about one thousand landfills collecting landfill biogas worldwide. The landfills that capture biogas in the US collect about 2.6 million tonnes of methane annually, 70% of which is used to generate heat and/or electricity. The landfill gas situation in the US was used to estimate the potential for additional collection and utilization of landfill gas in the US and worldwide. Theoretical and experimental studies indicate that complete anaerobic biodegradation of MSW generates about 200 Nm3 of methane per dry tonne of contained biomass. However, the reported rate of generation of methane in industrial anaerobic digestion reactors ranges from 40 to 80 Nm3 per tonne of organic wastes. Several US landfills report capturing as much as 100 Nm3 of methane per ton of MSW landfilled in a given year. These findings led to a conservative estimate of methane generation of about 50 Nm3 of methane per ton of MSW landfilled. Therefore, for the estimated global landfilling of 1.5 billion tones annually, the corresponding rate of methane generation at landfills is 75 billion Nm3. Less than 10% of this potential is captured and utilized at this time.

Full text

Methane generation in landfills
Nickolas J. Themelis

, Priscilla A. Ulloa
Earth Engineering Center and Department of Earth and Environmental Engineering, Columbia University,
New York, NY 10027, USA
Received 1 July 2005; accepted 15 April 2006
Available online 2 August 2006
Abstract
Methane gas is a by-product of landfilling municipal solid wastes (MSW). Most of the global
MSW is dumped in non-regulated landfills and the generated methane is emitted to the atmosphere.
Some of the modern regulated landfills attempt to capture and utilize landfill biogas, a renewable
energy source, to generate electricity or heat. As of 2001, there were about one thousand landfills
collecting landfill biogas worldwide. The landfills that capture biogas in the US collect about 2.6
million tonnes of methane annually, 70% of which is used to generate heat and/or electricity. The
landfill gas situation in the US was used to estimate the potential for additional collection and
utilization of landfill gas in the US and worldwide. Theoretical and experimental studies indicate that
complete anaerobic biodegradation of MSW generates about 200 Nm
3
of methane per dry tonne of
contained biomass. However, the reported rate of generation of methane in industrial anaerobic
digestion reactors ranges from 40 to 80 Nm
3
per tonne of organic wastes. Several US landfills report
capturing as much as 100 Nm
3
of methane per ton of MSW landfilled in a given year. These findings
led to a conservative estimate of methane generation of about 50 Nm
3
of methane per ton of MSW
landfilled. Therefore, for the estimated global landfilling of 1.5 billion tones annually, the
corresponding rate of methane generation at landfills is 75 billion Nm
3
. Less than 10% of this
potential is captured and utilized at this time.
r2006 Elsevier Ltd. All rights reserved.
Keywords: Landfill gas; Renewable energy; Municipal solid waste; Biogas; Methane emissions
ARTICLE IN PRESS
0960-1481/$ - see front matter r2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.renene.2006.04.020

Corresponding author. Tel.: 1 212 854 2138; fax: 1 212 854 5213.
E-mail addresses: njt1@columbia.edu (N.J. Themelis),pau2102@columbia.edu (P.A. Ulloa).

1. Introduction
Part of the methane generated in landfills can be captured and used as a renewable
energy source. In contrast, when methane is allowed to escape to the atmosphere, it has a
global warming potential that IPPC [1] estimates to be 23 times greater than that of the
same volume of carbon dioxide. In his 2003 review of energy recovery from landfill gas,
Willumsen [2,3] reported that as of 2001 there were about 955 landfills that recovered
biogas or landfill gas. The largest number existed in the US followed by Germany and
United Kingdom (Table 1). The capacity of most landfill gas-fuelled generators ranged
from 0.3 to 4 MW. While the largest biogas plant in the world is at the Puente Hills landfill,
close to Los Angeles California; the biogas is combusted in a steam boiler that powers a
50-MW turbine generator [4].
Willumsen also provided detailed information on 21 landfills in Denmark that in total
captured about 5800 Nm
3
of biogas/h, equivalent to 27.4 MW of contained thermal
energy. For comparison purposes, Denmark captures 20,000 tonnes of methane/y, while
the US captures 2,600,000 tonnes.
1.1. US landfilling
In 2002, the Earth Engineering Center of Columbia University collaborated with
BioCycle journal in a US-wide survey of the amount of municipal solid wastes (MSW)
generated in the US and how they were disposed [5,6]. The results are summarized and
compared with USEPA values [7] in Table 2 below.
ARTICLE IN PRESS
Table 1
Energy recovering landfills [3]
Country Number of plants
United States 325
Germany 150
United Kingdom 135
Sweden 70
Holland 60
Italy 40
Canada 25
Australia 25
Denmark 21
Norway 20
Austria 15
France 10
Spain 10
Switzerland 10
Finland 10
Poland 10
Brazil 6
Czech Republic 5
Hungary 5
China 3
Total 955

1.2. Global landfilling
The per capita generation of MSW in the US of 1.19 tonnes is twice as large as the total
generation (i.e. before any recycling) of MSW per capita in the affluent nations of E.U. and
Japan. This is expected because the consumption of materials and fossil fuels in the US,
with 5% of the world population, amounts to 20–25% of the total global consumption.
To arrive at a rough estimate of global landfilling, we started with the known rate of
landfilling in the US (220 million tonnes). The European Union (EU), and the rest of the
‘‘golden billion’’ who enjoy a high standard of living generate an estimated 420 million
tonnes of MSW of which at least 210 million tonnes (50%) are landfilled. Waste
management studies in developing nations, including some in Africa, have shown that the
MSW generation is always higher than 0.2 tonnes per capita, most of which is food and
yard wastes and is landfilled. This results in the estimate of 1080 million tonnes for the 5.4
billion people in the developing world. Adding up these estimates indicates that the global
MSW landfilled is somewhere close to 1.5 billion tonnes of MSW.
2. Landfill dumps and regulated landfills
Broadly, landfills can be classified into two types. The most common ones, still used
throughout the developing world, consist of dumps where the MSW is deposited until it
reaches a height that for esthetic or technical reasons is considered to be the desirable
maximum. After closing a landfill, some soil is deposited on top.
In October 1988, the US Environmental Protection Agency (USEPA) reported to the
Congress that municipal solid wastes were landfilled in nearly 6,500 landfills. Although
these landfills used a wide variety of environmental controls, they posed significant threats
to groundwater and surface water resources, as well as health effects due a threat to air and
water. To address these concerns, and standardize the technical requirements for MSW
landfills, USEPA promulgated revised minimum federal criteria for MSWLFs on October
9, 1991 [8]. As a result of these more stringent regulations, many of the smaller landfills
were closed and at the present time there are only 1767 landfills EPA [7]. Large landfill
operations have taken advantage of economies of scale by serving large geographic areas
and accepting other types of wastes, such as commercial solid waste, non-hazardous
sludge, and industrial non-hazardous solid wastes. In 2000, an estimated 75% of the US
municipal solid waste was deposited in 500 large landfills [9].
Regulated landfills are provided with impermeable liners and caps, and leachate
collection and treatment systems. Also, a system of gas wells and pipes collects as much as
ARTICLE IN PRESS
Table 2
Generation and fate of MSW in the US [5–7]
14th SOG survey [3,4] USEPA 2001 survey [5]
Million tonnes/yr (%) Million tonnes/yr (%)
Amount generated 336 100 211 100
Amount recycled and composted 90 26.7 65 30.8
Amount to waste-to-energy 26 7.7 27 12.8
Amount landfilled 220 65.6 119 56.4

possible of the landfill gas (LFG) and conveys it to a boiler or turbine where it is
combusted to generate heat or electricity, or is simply flared. When the landfilled area
reaches its maximum height, it is covered with an impervious layer so as to minimize entry
of rainwater and, thus, continuation of the bioreactions within the landfill. Also, US
landfill operators are required to continue collecting and treating gas and liquid effluents
for a period of 30 years after closure of the landfill.
A variation of the regulated landfill that is being tested in the US with some measure of
success is the ‘‘bioreactor’’ landfill. In this case, instead of preventing water from entering,
the aqueous effluent is recirculated and distributed throughout the landfill. The objective is
to accelerate the rate of biochemical degradation of the MSW, thus increasing the
generation of methane gas and, because of increased settling, the storage capacity of the
landfill.
The European requirements for non-hazardous, Class II landfills are similar to the US
and are based on the standards established by French regulations in January 1996.
However, the EU Landfill Directive of 1999 [10] requires that in the near future, landfilling
be limited to inert materials that are not biodegradable or combustible. Nevertheless, it
may take decades before this directive is applied in the new nations joining the EU, so the
generation of landfill gas will continue for the foreseeable future. In contrast to the EU and
Japan, landfilling remains the preferred means of MSW disposal in the US.
3. Composition of biomass in MSW
Table 3 is based on the characterization of US MSW [7]. Biomass materials, i.e. paper,
food and yard wastes, wood, leather, cotton and wool, constitute 69.5% of the MSW and
petrochemicals another 15%. The rest are inorganic materials such as metals, glass,
gypsum, and other minerals.
By using the ultimate (atomic) analysis of various types [11] of wastes and the atomic
weights of the respective elements, it was possible [12] to derive the composite molecular
formulae corresponding to mixed food wastes and paper:
Mixed food and green wastes: C
6
H
9.6
O
3.5
N
0.28
S
0.2.
Mixed paper: C
6
H
9.6
O
4.6
N
0.036
S
0.01.
It can be seen that sulfur and nitrogen are relatively minor components and occur
principally in mixed and green food wastes. Also, if one excludes nitrogen and sulfur, the
molecular structure of mixed paper is very close to cellulose, (C
6
H
10
O
5
)
x
. If one excludes
ARTICLE IN PRESS
Table 3
Characterization of US MSW by USEPA [7]
Biomass components (%) Petrochemical components (%)
Paper/board 36.2 Plastics 11.3
Wood 5.8 Rubber, nylon, etc.
a
3.7
Yard trimmings 12.1
Food scraps 11.7
Cotton, wool, leather
a
3.7
Total biomass 69.5% Total man-made 15.0%
a
Rubber, leather and textiles category of USEPA was assumed to be divided equally between natural and man-
made products.

the minor elements, the average molecular structure of organic compounds in MSW can be
approximated by the molecular composition C
6
H
10
O
4
[12]. It is interesting to note that this
composition corresponds to the structural formula of at least ten organic compounds, such as
ethyl butanedioic acid, succinic acid, adipic acid, ethylene glycol diacetate, and others. The
thermodynamic heat of formation of most of these compounds is about 960 MJ per kmol.
Landfill gas is a product of biodegradation of refuse in landfills, and it contains
primarily methane (CH
4
) and carbon dioxide (CO
2
), with trace amounts of non-methane
organic compounds (NMOC) that include air pollutants and volatile organic compounds
[13].Table 4 shows the main compounds and their proportion of LFG.
3.1. Anaerobic biodegradation of MSW in landfills
Shortly after MSW is landfilled, the organic components start to undergo biochemical
reactions. In the presence of atmospheric air, that is near the surface of the landfill, the
natural organic compounds are oxidized aerobically, a reaction that is similar to
combustion because the products are carbon dioxide and water vapor. However, the
principal bioreaction in landfills is anaerobic digestion that takes place in three stages. In
the first, fermentative bacteria hydrolyze the complex organic matter into soluble
molecules. In the second, these molecules are converted by acid forming bacteria to simple
organic acids, carbon dioxide and hydrogen; the principal acids produced are acetic acid,
propionic acid, butyric acid and ethanol. Finally, in the third stage, methane is formed by
methanogenic bacteria, either by breaking down the acids to methane and carbon dioxide,
or by reducing carbon dioxide with hydrogen. Two of the representative reactions are
shown below.
Acetogenesis
C6H12O6!2C2H5OH þ2CO2:(1)
Methanogenesis
CH3COOH !CH4þCO (2)
CO2þ4H2!CH4þ2H2O:(3)
The maximum amount of natural gas that may be generated during anaerobic
decomposition can be determined from the approximate, simplified molecular formula that
was, presented above:
C6H10O4þ1:5H2O¼3:25CH4þ2:75CO2:(4)
ARTICLE IN PRESS
Table 4
Composition of landfill gas [13]
Compound Average concentration (%)
Methane (CH
4
) 50
Carbon dioxide (CO
2
)45
Nitrogen (N
2
) 5
Hydrogen sulphide (H
2
S) o1
Non-methane organic compounds (NMOC) 2700ppmv

This reaction releases a very small amount of heat and the product gas contains
about 54% methane and 46% carbon dioxide. The biogas, or landfill gas, also contains
water vapor near the saturation point corresponding to the cell temperature, plus
small amounts of ammonia, hydrogen sulfide and other minor constituents. Therefore, in
order for anaerobic reaction to continue, it is necessary to supply the principal reagent,
water.
The ratio of the molecular weights of the composite organic compound (MW ¼146)
and water (MW ¼18) in Eq. (4) indicates that each kilogram of water can react
biochemically with 5.4 kg of organics. Since on the average, MSW contains at least 20%
moisture, there is just about sufficient moisture to react the contained biomass. However,
the anaerobic bacteria thrive at water concentrations above 40%, so continuous addition
of water is required.
3.2. Generation of methane per tonne of MSW
The typical MSW of Table 3 contains 69.5% of biomass materials. This includes the
contained moisture and inorganic dirt particles. Assuming that the dry organics amount to
60% of the biomass results in the estimate of 417 kg (2.86 kmol) of C
6
H
10
O
4
/tonne of total
MSW. A simple material balance based on Eq. (4) shows that complete reaction of one
tonne of MSW would generate 208 standard cubic meters of methane biogas or 0.149
tonnes of methane (1 kmol of CH
4
is equal to 22.4 Nm
3
).
We shall now compare the above theoretical numbers with reported data of anaerobic
digestion in the literature. The rate of biodegradation of MSW in landfills was studied by
Barlaz et al. [14] in small pilot plant columns that provided ideal temperature and
concentration conditions for bioreaction. As shown in Fig. 1, the reaction peaked
at less than one hundred days and was nearly complete after about 320 days. Barlaz [15]
estimated that the total amount of gas generated during this period was 213 Nm
3
ARTICLE IN PRESS
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0 100 200 300 400
Day
mL CH4/day-day gm
Methane Rate
M1
M2
Fig. 1. Generation of methane in experimental apparatus simulating landfill bioreactions (M1 and M2 denote two
different tests; [14]).

methane /dry tonne of biomass reacted (i.e. 0.153 tonnes methane /tonne of biomass). This
number is in good agreement with the theoretical calculation presented above.
An analysis of several anaerobic digestion operations by Verma [16] showed that the
reported rate of generation of biogas ranged from 100 to 200 Nm
3
of biogas (54–108 Nm
3
CH
4
) per tonne of wastes digested (estimated 60% biomass content). These numbers
correspond to generation rates from 73 to 135 Nm
3
methane per tonne of dry biomass.
Therefore, during the two weeks or so of digestion in the anaerobic digestion reactor, the
degree of bioreaction ranges from 35% to 65% of that projected by Eq. (4).
In an earlier publication, Barlaz et al. [17] reported that methane generation rates at a
landfill receiving 286,000 tonnes /y ranged from 0 to 90 Nm
3
/min. Assuming the mid-range
rate of generation of 45 Nm
3
per minute and that most of the gas is generated during the
first year after the MSW is landfilled, indicates that about 83 Nm
3
or 0.12 tonnes of
methane were generated /tonne of MSW.
It is interesting to note that the maximum capacity of landfilled MSW to produce
methane was reported by Franklin [18] to be 62 standard m
3
of methane per tonne of
MSW.
4. Estimates of global generation of methane from landfilling
USEPA estimated that the total anthropogenic emissions of methane were 282.6 million
tonnes in 2000 [19], of which 13% or 36.7 million tonnes were due to landfill emissions
(Fig. 2). We will now attempt to assess the accuracy of this number.
As shown earlier, the global MSW landfilled was estimated at about 1.5 billion tonnes of
MSW. If it is assumed, on the basis of the data presented above, that on the average the
methane generation is at least 50 Nm
3
of methane per tonne of MSW (i.e., at the low level
of reported anaerobic digestion rates), the global generation of methane from landfilled
MSW is in the order of 75 billion standard cubic meters or 54 million tonnes of methane.
Stern and Kaufman [20] extrapolated the 1985 estimate of Subak et al. [21] of 36 million
tonnes of CH
4
to earlier years, by assuming that MSW generation and landfilling were
ARTICLE IN PRESS
Manure
4%
Rice
11% Natural gas
15%
Coal
8%
Oil
1%
Solid waste
13%
Waste water
10%
Fuel stat, &
mobile
1%
Biofuel
combustion
4%
Biomass
burning
5%
Enteric
fermentation
28%
Global Anthropogenic CH4 Budget by
Source in 2000
Fig. 2. Global anthropogenic methane [19].

proportional to economic growth. On the basis of this assumption, and considering that
the global economic growth from 1985 to 2000 was 58% [22], the 36 million tonnes of
methane in 1985 extrapolate to 57 million tonnes in 2000. This number is in fairly good
agreement with the 54 million tonnes estimated by the present authors and is substantially
higher than the 36.7 million tonnes estimated by USEPA.
5. Capture of landfill gas
As mentioned earlier, modern landfills try to collect the biogas produced by anaerobic
digestion. However, the number of gas wells provided is limited (US average: about 1 well /
4000 m
2
of landfill [18]), so that only part of the biogas is actually captured.
Table 5 presents reported captured and estimated loss of methane for 25 landfills in
California. The landfilled MSW is reported by California Integrated Waste Management
Board [23] and the captured biogas was reported by Berenyi [24] and converted to methane
by multiplying by 54%. On the average, the captured methane amounted to 43 Nm
3
per
tonne of MSW and the estimated methane loss to 82 Nm
3
per tonne of MSW.
ARTICLE IN PRESS
Table 5
Landfill methane in California [23,24]
Landfill name MSW
(Tonnes/yr)
Captured CH
4
(Nm3/yr)
Captured CH
4
(Nm
3
/t MSW)
Assumed
generation
(Nm
3
/t MSW)
Estimated loss
CH
4
(Nm
3
/
t MSW)
Altamont 1,157,312 24,001,656 21 122 101
Scholl Canyon 412,429 50,237,893 122 122
Azusa 157,445 17,056,769 108 122 14
Puente Hills #6 3,377,867 200,549,669 59 122 63
Bradley Avenue West 418,341 40,190,314 96 122 26
Crazy Horse 151,258 4,822,838 32 122 90
Monterey Peninsula 197,797 3,351,872 17 122 105
Prima Deshecha 703,051 11,253,288 16 122 106
Olinda Alpha 1,877,620 17,862,362 10 122 112
Frank Bowerman 1,991,666 20,095,157 10 122 112
Sacramento Co (Kiefer) 615,702 16,076,126 26 122 96
Colton Refuse Disposal
Site
305,682 13,664,707 45 122 77
San Timoteo 158,405 2,154,647 14 122 108
Otay Annex 1,267,641 11,164,869 9 122 113
Miramar 1,289,295 28,334,172 22 122 100
Sycamore 817,255 6,695,706 8 122 114
Tajiguas 200,084 9,766,246 49 122 73
Newby Island 592,877 17,683,738 30 122 92
Kirby Canyon 246,902 3,633,204 15 122 107
Guadalupe Disposal Site 166,915 8,038,063 48 122 74
Santa Cruz City 51,191 3,351,872 65 122 57
Buena Vista Disposal Site 131,775 4,420,935 34 122 88
Woodville Disposal Site 61,368 4,822,838 79 122 43
Visalia Disposal Site 108,327 8,038,063 74 122 48
Yolo County Central 163,841 10,449,482 64 122 58
Average 43 82

6. Generation and utilization of landfill gas in the US
Berenyi reported that as of 1999, there were 327 LFG-to-energy plants in the US [24].
Table 6 summarizes the different uses of landfill gas. Fig. 3 shows that slightly less than
three-fourths (71%) or 231 LFG-to-energy plants produce electricity. About one-fifth
(21%) sell their gas to a direct user, approximately 4% of the plants produce pipeline—
quality gas, and approximately 3% use the gas to produce synthetic fuels or for other uses.
(Fig. 3).
ARTICLE IN PRESS
Table 6
Utilization of landfill gas [13]
Direct heating applications |Use for industrial boilers
|Space heating and cooling (e.g.greenhouses)
|Industrial heating/cofiring
Electricity generation applications |Processing and use in reciprocating internal combustion (RIC)
engines (stoichoimetric or lean combustion)
|Processing and use in microturbines, gas, and steam turbines
|Processing and use in fuel cells
Feedstock in chemical
manufacturing processes
|Conversion to methanol (industrial or vehicular use)
|Conversion to diesel fuel (vehicular fuel)
Purification to pipeline quality gas |Utilization as vehicular fuel
|Incorporation into local natural gas network
Soil remediation |Leachate evaporation system.
Heat recovery from landfill flares |Using organic Rankine cycle
|Using Stirling cycle engines
Uses of LFG-to-Energy Plants in US
Electricit
y
72%
Pipeline Quality
4%
Direct Heating
21%
Synfuel/Other
3%
Fig. 3. Types of landfill gas utilization in the United States [24].

Fig. 4 provides a breakdown of the US landfill gas used for energy generation in each
state. California has the largest number of landfill gas facilities, with 65 plants, because of
state and local requirements resulting in the collection and control gas. Other states with
significant number of plants include Illinois (43), Michigan (22), New York (20) and
Pennsylvania (19).
Table 7 provides some characteristics of the landfill gas projects by each state. The total
active area of landfills provided with landfill gas collection is around 21,000 ha, while a
little more than the half of this area is devoted to methane recovery (12,000 ha). The states
of California, Illinois, Michigan, New York and Pennsylvania represent approximately
50% of total of devoted area to methane recovery. On the other hand, California,
New York, Illinois, Texas and Michigan represent about 60% of total of refuse buried in
landfills with gas collection.
The average landfill depth in the gas-collecting landfills ranges from 14–53 m; the nation-
wide average depth is 28 m. The density of the MSW buried in these landfills ranges from
594 to 832 kg/m
3
, while the national average is estimated at 732 kg /m
3
.
Table 8 provides data related with landfill gas collection by state, and also considers the
amount of municipal solid waste landfilled annually in each state (Solid Waste Digest [25]).
The largest amount of MSW landfilled is landfilled in California, with around 35 million
tonnes /y. Other significant landfillers are Pennsylvania, Texas, Illinois, Michigan, and
Ohio.
The total landfill gas collected is around 7 billion Nm
3
annually, while the landfill gas
processed (i.e. excluding flaring) is 5 billion Nm
3
annually and represents about 70% of the
biogas collected. The states of California, Illinois, Michigan, Pennsylvania and New York
represent 60% of total of landfill gas processed to generate energy (heat, electricity or fuel).
The heating value of untreated landfill gas ranges from 464 to 591 kJ /Nm
3
(average:
540 kJ Nm
3
).
ARTICLE IN PRESS
Number of LFG-to Energy Plants per State in 1999
0 10203040506070
WI
VA
TX
SC
PA
NC
NJ
MO
MA
LA
IA
HI
DE
CA
AL
Number
Fig. 4. Number of landfill gas to energy plants per state [24].

7. Electricity generation
The US Environmental Protection Agency(USEPA), operates a Landfill Methane
Outreach Program that encourages landfill owners to develop gas recovery projects
wherever it is feasible.USEPA estimates that over 700 landfills across the United States
could install economically viable landfill gas energy recovery systems, but only 380 energy
recovery facilities were in place in 2004 [26]. Currently, 295 of these facilities generate
electricity; the rest use landfill gas for heating, reducing volume of leachate, etc.
ARTICLE IN PRESS
Table 7
Characteristics of LFG projects by state [24]
State Number of LFG
projects
Active area Devoted area
CH
4
recovery
Refuse buried Average
depth
Average density
refuse
(ha) (ha) (tonnes) (m) (kg/m
3
)
Alabama 2 236 16 1,306,359 14 653
Arizona 5 285 254 17,418,126 29 693
Arkansas 1 57 57 4,717,409 18 772
California 65 5,746 3,570 546,179,234 36 730
Colorado 1 36 36 27,215,821 26
Connecticut 5 147 109 12,655,357 32 733
Delaware 2 146 53 8,527,624 23 653
Florida 12 697 530 69,971,877 25 731
Georgia 4 160 68 15,694,457 24 698
Hawaii 1 17 17 1,195,500 23 594
Illinois 43 1,743 1,087 117,968,430 26 814
Indiana 4 163 93 10,886,329 22 832
Iowa 3 210 62 11,974,961 23 761
Kansas 3 482 77 19,958,269 18 713
Kentucky 1 304 122 n/a 46 891
Louisiana 2 209 122 n/a 53
Maryland 4 233 128 14,424,385 21 624
Massachusetts 16 345 267 20,638,665 25 752
Michigan 22 1,038 697 67,676,676 24 744
Minnesota 5 190 158 20,303,003 25 743
Missouri 2 100 37 12,185,430 46 594
New Hampshire 6 158 151 10,646,829 28 713
New Jersey 11 770 492 62,367,776 23 790
New York 20 1,050 619 152,041,187 38 812
North Carolina 15 723 435 31,942,937 24 695
Ohio 6 383 245 47,718,407 23 792
Oregon 5 531 139 14,116,847 29 812
Pennsylvania 19 1,496 572 64,773,655 32 736
Rhode Island 1 62 47 10,886,329 46 653
South Carolina 4 84 37 5,663,612 18 653
Tennessee 3 181 116 12,428,558 35 793
Texas 8 865 475 117,730,352 22 730
Vermont 2 24 13 1,327,225 25 653
Virginia 7 347 190 29,393,087 26 754
Washington 5 663 364 35,017,690 34 817
Wisconsin 12 546 289 39,335,934 25 759
Total 327 20,426 11,742 1,636,288,340
The reported data corresponds to 36 states (modified from Berenyi).
Note: n/a: no available.

Through the Outreach Program, USEPA is working with municipal solid waste landfill
owners and operators, states, utilities, industry and other federal agencies to lower the
barriers to economic landfill gas energy recovery.
Table 9 compares the electricity generated by landfill gas to energy plants in each state
according to Berenyi [24] and USEPA [26]. The amount of landfill gas processed is around
5 billion Nm
3
(Table 8), and generates about 912,000 kW, equivalent to 8 billion kWh /
annum (Table 9).
ARTICLE IN PRESS
Table 8
Landfill gas capture by state [24,25]
State MSW landfilled
(solid wastes
digest)
Landfill gas
captured
(Berenyi)
Landfill gas used
(Berenyi)
LFG
processed
Heating value
untreated gas
(tonnes/yr) (Nm
3
/yr) (Nm
3
/yr) (%) (KJ)
Alabama 5,110,224 446,559 446,559 100 580
Arizona 6,460,129 8,186,916 n/a n/a 531
California 35,188,243 1,952,168,440 1,408,295,409 72 500
Colorado 6,269,618 3,096,143 3,096,143 100 514
Connecticut 257,643 55,819,881 20,497,060 37 543
Delaware 1,587,590 38,538,046 20,675,684 54 501
Florida 16,248,753 245,796,024 189,780,153 77 550
Georgia 10,827,361 33,581,240 33,581,240 100 563
Hawaii 595,119 21,702,770 21,702,770 100 528
Illinois 17,972,421 635,117,780 486,899,870 77 547
Indiana 6,097,251 66,983,857 21,137,128 32 522
Iowa 1,835,254 20,675,684 20,675,684 100 554
Kansas 2,835,889 36,179,553 36,179,553 100 528
Kentucky 4,486,075 21,434,834 n/a n/a n/a
Maryland 2,849,497 53,333,829 31,005,877 58 543
Massachusetts 1,406,151 203,407,647 111,848,156 55 535
Michigan 16,686,020 455,795,378 417,920,820 92 559
Minnesota 1,978,590 135,977,230 131,065,081 96 513
Missouri 4,066,951 56,564,146 37,213,254 66 580
New Hampshire 1,629,321 72,238,369 72,238,369 100 574
New Jersey 3,594,303 350,548,853 223,279,524 64 534
New York 6,647,011 445,472,421 336,958,573 76 543
North Carolina 6,630,681 113,296,992 85,221,081 75 552
Ohio 12,572,802 182,970,127 124,566,158 68 563
Oregon 4,870,725 16,954,359 16,954,359 100 520
Pennsylvania 22,458,496 556,625,930 363,379,983 65 545
Rhode Island 1,375,306 86,334,749 86,334,749 100 570
South Carolina 5,271,705 14,260,119 11,163,976 78 563
Tennessee 5,877,710 79,963,840 35,665,183 45 591
Texas 21,501,406 312,839,422 278,768,621 89 547
Vermont 410,052 6,981,206 6,981,206 100 475
Virginia 12,157,307 104,078,029 77,403,568 74 563
Washington 4,692,008 253,050,127 13,099,065 5 464
Wisconsin 6,263,268 199,492,812 184,160,952 92 540
Total reporting 253,814,753 6,811,497,272 4,901,214,602

In the more recent survey by USEPA [24] the amount of electricity generated from
landfill gas was estimated at 1.07 GW.
8. Conclusions
On the basis of the theoretical and experimental information presented above, it can be
assumed that, under the right conditions, at least 50% of the ‘‘latent’’ methane in MSW
can be generated within one year of residence time in a landfill, while the landfilled area is
not capped and rainfall can penetrate into the landfilled mass. This would correspond to
about 50 Nm
3
of methane /tonne of a typical MSW. However, the 25 California landfills
that we examined in detail captured only 43 Nm
3
of methane per tonne landfilled. Of
course, conventional landfills are far from perfect bioreactors. Also, we have no
information as to the effectiveness of the gas collection of these landfills.
Nearly three hundred eighty landfills in the US capture 3.7 billion Nm
3
of methane (2.6
million tonnes) of which 70% is used to generate thermal or electrical energy. The rest is
flared, because it is not considered to be of economic use. There are nearly 1400 landfills
that do not capture any biogas.
If it were possible to build and operate bioreactor landfills, where water is added and
nearly all the generated methane is captured, the methane collected in the US, at an
assumed average rate of 50 Nm
3
of methane per tonne of MSW, would amount to 11
billion Nm
3
of methane, i.e. three times the amount that is presently captured.
With regard to the global picture, an ongoing study [27] estimated the global disposition
of MSW in landfills to be 1.5 billion tons of MSW. The corresponding generation of
methane is estimated to about 50 million tonnes, of which only a total of 5 million tonnes
ARTICLE IN PRESS
Table 9
Electricity generation by using LFG [24,26]
State Electricity produced (kW) State Electricity produced (kW)
Berenyi 1999 USEPA 2005 Berenyi 1999 USEPA 2005
Alabama 4,000 n/a Missouri 800 n/a
Arizona 18,425 10,350 Nebraska n/a 3,200
California 237,570 255,935 New Hampshire 15,700 13,800
Colorado 800 n/a New Jersey 48,900 45,700
Connecticut 9,840 5,000 New York 46,047 48,300
Delaware 1,500 n/a North Carolina 10,350 11,600
Florida 19,800 39,830 Ohio 8,500 36,200
Georgia 5,400 7,400 Oregon 5,660 5,600
Hawaii 3,000 n/a Pennsylvania 46,350 68,400
Illinois 177,766 153,934 Rhode Island 12,000 17,000
Indiana 7,525 21,585 South Carolina n/a 8,400
Iowa 8,500 6,400 Tennessee 7,000 7,200
Kansas 3,000 n/a Texas 15,600 57,656
Kentucky n/a 10,400 Vermont 1,500 1,200
Maryland 7,250 8,050 Virginia 14,600 31,800
Massachusetts 27,650 37,744 Washington 15,700 15,200
Michigan 79,900 72,300 Wisconsin 29,000 47,375
Minnesota 25,800 24,200 Total 911,433 1,071,759

are captured at this time. Therefore, methane emissions to the atmosphere are in the order
of 45 million tonnes. Since methane has 23 times the global warming potential of carbon
dioxide (CO
2
), global landfill emissions correspond to about one billion tonnes of CO
2
.
Acknowledgements
The authors gratefully acknowledge the provision of experimental data and other
assistance of Prof. Morton Barlaz of North Carolina State University, the compilation of
landfill biogas data by Dr. Eileen Berenyi of Governmental Advisory Associates, and the
support of research at Columbia University by the Waste-to-Energy Research and
Technology Council (www.columbia.edu/cu/wtert).
References
[1] Energy Information Administration. Emissions of Greenhouse Gases in the United States 2003. Comparison
of global warming wotentials from the IPCC’s second and third assessment reports; http://www.eia.doe.gov/
oiaf/1605/ggrpt/global.html
[2] Willumsen H. Experience with landfill gas recovery plants. Renewable Energy 2003; www.sovereign-publications.
com/renewable-energy2003-art.htm
[3] Willumsen H. Energy recovery from landfill gas in Denmark and worldwide; www.lei.lt/Opet/pdf/
Willumsen.pdf
[4] California Energy Commission. Landfill gas-to-energy potential in California; 2002; http://www.energy.
ca.gov/reports/2002-09-09_500-02-041V1.pdf
[5] Themelis NJ, Kaufman SM. Waste in a land of plenty. Waste Management World; Sept–Oct 2004p. 23—8.
[6] Kaufman SM, Goldstein N, Millrath K, Themelis NJ. The state of garbage in America. BioCycle 2004:31–41.
[7] USEPA. Municipal solid waste generation, recycling, and disposal in the United States, Facts and Figures;
2003;www.epa.gov/epaoswer/non-hw/muncpl/pubs/msw05rpt.pdf
[8] Code of Federal Regulations. Title 40:Protection of Environment, part 258-Criteria for municipal solid waste
landfills; http://www.epa.gov/epacfr40/chapt-I.info/chi-toc.htm
[9] USEPA. Development document for final effluent limitations guidelines and standards for the landfills point
source category. EPA-821-R-99-109. Washington, DC; 2000; http://www.epa.gov
[10] European Union. Council directive 99/31/EC; http://europa.eu.int/comm/environment/waste/landfill_
index.htm
[11] Tchobanoglous G, Theisen H, Vigil S. Integrated solid waste management., Chapter 4. New York: McGraw-
Hill; 1993.
[12] Themelis NJ, Kim HY. Material and energy balances in a large-scale aerobic bioconversion cell. Waste
Manage Res 2002;20:234–42.
[13] Energy Information Administration. US Department of Energy. Growth of the landfill gas industry;1996;
http://www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/chap10.html
[14] Barlaz M, Cowie S, Staley B, Hater G. Production of NMOCs and trace organics during the decomposition
of refuse and waste components under anaerobic and aerobic conditions. third intercontinental landfill
research symposium Nov 29th–Dec 2nd; 2004.
[15] M Barlaz, North Carolina State University, private communication to P.A. Ulloa.
[16] Verma S, Themelis NJ. Anaerobic digestion of organic waste in MSW. Waste management world, 2004; Jan.
–Feb, 20–4. (See also Verma S, M.S. thesis, Earth and Environmental Engineering, Columbia University,
2003, www.columbia.edu/cu/wtert, Publications).
[17] Barlaz MA, Rooker AP, Kjeldsen P, Gabr MA, Borden RC. A critical evaluation of factors required to
terminate the post-closure monitoring period at solid waste landfills. Environ Science & Technol
2002;36(16):3457–64.
[18] USEPA. The role of recycling in integrated waste management in the US. Franklin Associates. Municipal
Industrial Waste Division, Washington, DC, EPA/530-R-96-00; 1995.
[19] USEPA. International analyses of methane emissions; 2002; www.epa.gov/methane/intlanalyses.html
ARTICLE IN PRESS

[20] Stern DI, Kaufmann RK. Annual estimates of global anthropogenic methane emissions: 1860–1994. trends
online: a aompendium of data on global change. carbon dioxide Information Analysis Center, Oak Ridge
National Laboratory, US Department of Energy, Oak Ridge, Tennesse, USA; 1998; http://cdiac.esd.
ornl.gov/trends/meth/ch4.htm
[21] Subak S, Raskin P, Von Hippel D. National greenhouse gas accounts: current anthropogenic sources and
sinks. Climate Change 1993;25:15–28.
[22] Earth Policy Institute. Economic grow falters: historical time series from David Malin Roodman. In
Worldwatch Institute, vital signs; 2002 p. 58–9; http://www.earth-policy.org/Indicators/Econ/Econ_data.htm
[23] California Integrated Waste Management Board; http://www.ciwmb.ca.gov/landfills/Tonnage/2003/
Landfill.htm
[24] Berenyi E. Methane recovery from landfills yearbook, 5th ed. Westport, CT: Governmental Advisory
Associates; 1999.
[25] Solid waste digest special report. Landfill capacity, vol. 14 2004 No. 9 http://www.wasteinfo.com
[26] USEPA. Landfill Gas Outreach Program; http://www.epa.gov/lmop/proj/index.htm
[27] Earth Engineering Center. Landfill gas generation, capture, and utilization. Study in progress; 2005.
ARTICLE IN PRESS