-------
o
TABLE 3. COMPOSITION AND ANALYSIS OF AN AVERAGE MUNICIPAL REFUSE FROM STUDIES BY PURDUE UNIVERSITY
Component
Paper
Wood
Grass
Brush
Greens
Leaves
Leather
Rubber
Plastic
Oils, Paints
Linoleum
Rags
Street
Sweepings
Dirt
Unclassified
Garbage
Fats
Percent
of All
Refuse
by Weight
42.0
2.4
4.0
1.5
1.5
5.0
0.3
0.6
0.7
0.8
0.1
0.6
3.0
1.0
0.5
10.0
2.0
Moisture
(Percent
by
Weight)
10.2
20.0
65.0
40.0
62.0
50.0
.10.0
1.2
2.0
0.0
2.1
10.0
20.0
3.2
4.0
72.0
0.0
Volatile
Matter
Carbon
Analysis
Hydrogen
(Percent Dry Weight)
Oxygen
Nitrogen
Sulfur
Noncom-
bustibles
Rubbish, 64%
84.6
84.9
_
_
70.3
_
76.2
85.0
-
-
65.8
93.6
67.4
21.2
-
Food
53.3
43.4
50.5
43.3
42.5
40.3
40.5
60.0
77.7
60.0
66.9
48.1
55.0
34.7
20.6
16.6
5.8
6.0
6.0
5.9
5.6
6.0
8.0
10.4
7.2
9.7
5.3
6.6
4.8
2.6
2.5
44.3
42.4
41.7
41.2
39.0
45.1
11.5
-
22.6
5.2
18.7
31.2
35.2
4.0
18.4
0.3
0.2
2.2
2.0
2.0
0.2
10.0
-
-
2.0
0.1
4.6
0.1
0.5
0.05
0.20
0.05
0.05
0.05
0.05
0.05
0.40
2.0
-
-
0.40
0.13
0.20
0.01
0.05
6.0
1.0
6.8
8.3
13.0
8.2
10.1
10.0
10.2
16.3
27.4
2.5
25.0
72.3
62.5
Wastes, 12%
45.0
76.7
Noncombustibles
Metals
8.0
Glass & Ceramics 6.0
Ashes
ATI Refuse
10.0
100
3.0
2,0
10.0
20.7
0.5
0.4
3.0
Composite
-
0.8
0.6
28.0
Refuse, as
28.0
6.4
12.1
, 24%
0.04
0.03
0.5
Received
3.5
28.8
11.2
0.2
0.1
0.8
22.4
3.3
0.0
_
-
*
0.33
0.52
0.00
_
-
0.5
0.16
16.0
0.0
99.0
99.3
70.2
24.9
-------
cases.
In addition to these equation inaccuracies in the amount of gas pro-
duced, there is the likelihood that the composition of the gas measured
at the landfill will not be as calculated because of the much higher solu-
bility of carbon dioxide in water than methane, among other reasons. Sol-
ubility considerations alone suggest that the greater the availability of
water in a landfill and the greater the moisture content of the refuse, the
higher will be the methane concentration in the gas even though the amount
of gas generated per gram of refuse remains unchanged.
The overall reactions for the anaerobic decomposition of typical solid
waste components to form methane are as follows: For cellulose which is a
major component of refuse, conversion begins with hydrolysis or enzymatic
breakdown of saccharides, of which glucose is the most common. The glucose
then breaks down according to:
C6H12°6* 3 CH4 + 3 C02
by pathways as yet uncertain, involving organic acids and acetate, in parti-
cular, and probably hydrogen as intermediates. A fatty material such as
stearic acid degrades according to:
CioH,eO, + 8 H00 »- 13 CH, + 5 C00
10 00 C. C. 4 L
To the extent specific compounds in the waste can be determined, it is
possible to refine the result obtained from the overall refuse composition.
Golueke, for example, divided the organic portion of the solid waste into
newsprint (33 percent), Kraft paper (40 percent), and other organics (27 per-
cent) to calculate a,total gas production of 0.55 cu m/kg (8.8 cu ft/lb)
dry volatile matter. Such an approach reduces the errors inherent in use
of the overall elemental analysis, and is particularly useful for incorpo-
rating rate constants to predict the effect on non-homogeneous decomposition
rates from component to component.
Gas Quantity
Reliable data on total gas production from decomposition of waste are
difficult to obtain as is borne out by the high variability of available
data. Ideally, a landfill must be monitored over its entire decomposition
life to determine total gas production. Obviously, the time required to
develop such information is an obstacle. An additional problem inherent in
measuring gas production is the change in landfill conditions brought about
by the gas collection techniques. If one attempts to enclose a landfill for
gas measurement, using a wetted clay seal, for example, the decomposition
process will be changed, affecting the results directly. Water movement in
the landfill will be changed, normal gas flow patterns will be disrupted,
etc., possibly invalidating the results. Small volumes of refuse have been
decomposed in lysimeters and the gases evolved measured, but the difficul-
ties in simulating not only typical landfill conditions but also the varia-
tions in conditions brought about by climatic events makes the applicabil-
17
-------
ity of such data to full-scale landfills questionable. Many studies which
might have produced gas generation data are useless as far as methane pro-
duction is concerned because methane production was never achieved. In some
cases insufficient time was allowed and in other cases the decomposition
process did not advance to stable methane production for some unexplained
reason. The fact is that it has been difficult to achieve stable methane
production in small enclosed volumes (lysimeter studies).
Table 4 summarizes the best available data on total gas generation
from solid waste during methane formation. Additional estimates or measured
values exist, but these values are not thought to accurately reflect the
latest state-of-knowledge. Necessarily, the higher gas production values
are based on theoretical calculations. The nature of decomposition of
materials of varied composition and degrees of decomposability suggests that
complete decomposition will take a very long time and, in fact, may never
be attained completely in practice. One way to circumvent this problem is
to relate gas production to the amount of refuse decomposed (e.g., volatile
solids or organic carbon lost) and leave it to the user of the data to de-
termine how much decomposition will be of interest for the particular appli-
cation or landfill of concern.
Table 4 indicates that the theoretical gas production is approximately
0.44 cum/kg (7 cu ft/lb) of refuse for complete decomposition by methane
formers and their associated microbiological co-workers (entries 1, 2, 10,
11, and 12). Variations are due primarily to waste composition differences.
Entry 11 is based on measurement of gas collected from a large landfill over
a period of one year by a gas withdrawal system installed to limit uncon-
trolled off-site gas migration. By estimating the tonnage of refuse gener-
ating gases which were pumped into the collection system, and knowing the
composition and amount of those gases, a value for gas generation per unit
refuse weight was calculated over the period of monitoring. Adjustment of
constants appropriate to theoretical equations describing the rate of gas
generation with time, permited extrapolation of the rates measured over a
relatively short time to the total production to be expected over the life
of the landfill. Note that the total amount of gas to be produced was
based on purely theoretical considerations (generation period and rate of
change), and the curves developed were constrained by the calculated total
to be produced and on that measured for one year. Therefore, entry 11
total gas production agrees with other purely theoretical approaches.
Consideration of the decomposability of various components of the
waste reduces the total gas production to a more feasible maximum of 0.13
to 0.31 std cu m/kg (2 to 5 std cu ft/lb) (entries 3 and 4). The
highest measured amounts of gas were produced in digesters in which solid
waste was seeded with sewage sludge; mixing provided uniformity of condi-
tions, substrate, and nutrients; and variables such as temperature, time and
moisture content were controlled to various degrees to promote methane for-
mation. These results may be practical for controlled decomposition of waste
slurries in specially built digesters designed for that purpose, but they are
not applicable to landfill conditions except, possibly, as a goal which will
probably prove unrealizable even for specially designed and operated land-
18
-------
TABLE 4. TOTAL LANDFILL GAS (CARBON DIOXIDE AND METHANE) GENERATION FROM MUNICIPAL SOLID WASTE
Gas production
1.
2.
3.
Sources
Anderson & Callinan (17)
Boyle (13)
Golueke (16)
Conditions
Typical municipal refuse
Typical municipal refuse
Divided organics by component,
Basis
Theoretical
Theoretical
Theoretical
I V» s^ \» M V 1 l*WV*t*^V4
std cu m/kg
0.41
0.45
0.30
4. Pacey (18)
5. Klein (19)
6. Hitte (20)
7. Pfeffer (21)
8. Schwegler (22)
9. Hekimian, et al (23)
calculated 0.55 cu m/kg dry
volatiles*
Weighted organic components by
degradability, calculated 0.06
cu m CH,/kgt
Digested refuse with sewage
sludge, obtained 0.44 cu m/kg
volatiles destroyed*
Cites data for digesting refuse
and sewage sludge of 0.11 cu m
ClWkg refuse and sludge, recal-
culated assuming wet sludge is
negligible1"
Digested refuse at 8 percent solids,
35°C, 30 day solids ret. time
0.38 cu m/kg refuse destroyed,
assumes refuse 50 percent decom-
posable
0K"°rved value for Los Angeles
area
Theoretical
Estimated
Estimated
0.12
Lab measurement 0.24
Lab measurement 0.21
Lab measurement 0.26
0.19
0.05
(continued)
-------
ro
TABLE 4 (continued)
Sources
Conditions
Basis
Gas production
refuse as received*
stri cu m/kg
10. Alpern (24)
11. City of Los Angeles (25)
12. Bowerman, et al (3)
13. Blanchet (1)
530 cu m/t refuse
387 cu m/t refuse, theoretical
extrapolation of measured values
0.51 cu m/kg dry refuse, recalcu-
lated* based on 0.25 kg org. C/kg
Calculated from landfill test and
theoretical extrapolation over 10 yr
14. VTN Consolidated, Inc. (26) "Estimate" for Los Angeles landfills
15. Merz (27)
16. Merz & Stone (28)
17. Rovers & Farquhar (29)
18. Streng (30)
19. Chian (31)
Refuse in small lysimeters, wetted
with digester supernatant
Lysimeter, gas production very low
at end of 2-1/2 yr study
Lysimeter, gas prod, continuing at
low level at end of 200 day study
Lysimeter, gas. prod, over approxi-
mately 2 yr, continuing
Small lysimeters, cell 4 only one
producing CH4, gas prod, low after
300 days, recalculated*
Theoretical
Measurement/
theoretical
Measurement
Measurement
Measurement
Measurement
Measurement
.* Corrected to refuse composition of Table 3.
t Corrected to 53 percent CH^.
0.53
Theoretical/mea- 0.39
surements in
landfill
0.40
0.13
0.05
0.013
0.004
0.003
0.039
0.0005
-------
fills. Entries 5, 6, and 7 are examples of digester gas production, 0.22 to
0.25 std cu m/kg (3.5 to 4 std cu ft/lb) of refuse being a representa-
tive range. Entry 7, in particular, provides information on the effect of
temperature and solids contact time (e.g., the average period of contact be-
tween waste to be decomposed and the micro-organisms), both of which are
cited previously as being important landfill variables affecting gas produc-
tion.
Entries 8, 9, and 14 reflect the most common approach for estimating
total gas production; namely, evaluating available information and estimat-
ing what is believed to represent a reasonable value for the case in ques-
tion. For example, one rule of thumb often cited reasons that 0.83 cu m/kg
(6 cu ft/lb) is approximately the maximum theoretical gas production from
typical refuse, of which one-half will not be generated because of imprefec-
tions in the various decompositional processes, resulting in incomplete de-
composition. Of this, another half will be lost because it is not produced
during the period of active decomposition when gas recovery would be most
likely. Finally, only one-half of the amount will be feasible to recover;
the remainder being produced near landfill boundaries or between withdrawal
wells, etc., and therefore lost. The result is that only 0.047 std cu m
of gas/kg (0.75 std cu ft of gas/lb) of refuse is likely to be recovered.
Such rules of thumb, tempered by the sparse but steadily increasing amount
of field and pilot scale data, has led to commonly accepted figures, such as
used in entries 8, 9, and 14.
Entries 15 through 19 are generation rates measured in enclosed test
chambers (lysimeters) containing refuse and, so, depart from landfill con-
ditions to varying degrees. Water was added in abnormal amounts in some
cases, and had the effect of promoting methane formation. Data from such
tests are among the best sources for estimating production figures, how-
ever, and must be given considerable weight in assessing likely gas genera-
tion from landfills. None of the production data from these studies is
based on total refuse decomposition nor total conceivable gas production
from the refuse tested. Rather, the period of most active methane genera-
tion apparently was observed. In most cases the production rates had
dropped off, but not virtually ceased by the conclusion of monitoring. The
different amounts of gas produced in the five studies most likely are due
to differences in conditions in the lysimeters, such as moisture content,
moisture flow, temperature, and other variables. Entry 17, in particular,
was carried out over a relatively short period of time and conditions in the
lysimeter including temperature and pH were not conducive to methane forma-
tion. Such factors undoubtedly caused the low generation figure, which is
lower than that to be expected from full-scale landfills under reasonable
conditions. Adverse conditions and difficulties in simulating landfill con-
ditions are likely to be responsible for the very low figure of entry 19 as
well. The 0.013 to 0.038 std cu m/kg (0.2 to 0.6 std cu ft/lb) range
of entries 15 and 18 is likely to be closest of the five tests to actual gas
production from a landfill in a humid climate. Note further that this quan-
tity corresponds well with other practical values in Table 4.
21
-------
Gas Composition
Gas composition data is much easier to determine and is, therefore,
more readily available than is data on total gas production. Data never-
theless vary widely and gas composition in landfills has been recorded from
0 to 70 percent methane and from 0 to 90 percent carbon dioxide. Aerobic
decomposition should produce a number of moles of carbon dioxide equal to
the number of moles of oxygen consumed, so theoretically, any carbon dioxide
concentration higher than 20 percent indicates that processes other than
aerobic decomposition are involved. However, carbon dioxide concentrations
less than 20 percent do not necessarily indicate that only aerobic decom-
position is occurring because of the high solubility of carbon dioxide in
water which lowers the carbon dioxide concentration in the gas as more
moisture is added.
Facultative anaerobic decomposition produces the maximum carbon diox-
ide concentration and values up to 90 percent have been recorded. Once
the methane formation stage of decomposition is attained, carbon dioxide
concentrations range generally from 40 to 50 percent. The exact value de-
pends on the composition of the refuse being decomposed at that time; the
amount, movement and chemical characteristics of moisture which influence
the amount of carbon dioxide dissolved; and the rate of decomposition. A
value of 45 percent is typical for full-scale actively decomposing landfills.
The methane concentration is affected more strongly by particular
landfill characteristics than is the carbon dioxide concentration, reflect-
ing the narrow range of landfill conditions suitable to methane formers.g
The methane concentration is normally within the 45 to 65 percent range,
with the most common values generally in the 45 to 55 percent range. Assum-
ing active methane formation, properly balanced with associated acid for-
mers, variations in methane concentration are caused by the specific composi-
tion of the waste, the components being degraded at a particular time, and
by variations in carbon dioxide solubility noted previously. If improper
balance is achieved between the methane and acid formers, the methane concen-
tration will be lowered, other factors being equal. The importance of waste
composition is illustrated by substituting the elemental analyses of the
paper and fat fractions found in Table 3 into the overall equations for me-
thanogenic decomposition. This indicates that the gas produced from paper
degradation will be basically 51 percent methane and 49 percent carbon diox-
ide, whereas, from fats the gas composition will be 71 percent methane and
29 percent carbon dioxide.
It is important to review some of the reasons why a given landfill may
depart from the typical gas production and composition figures shown in
Tables 3 and 4. Overall waste composition is an obvious consideration and
the composition of the matter decomposing at a particular point in^space and
time determines the gas generation rate and composition at that point.
Methane formation does not occur over the entire period of decomposi-
tion in a landfill; therefore, conditions limiting or precluding stable me-
thane formation at any time throughout a landfill's history until complete
stabilization has occurred will affect gas production directly.
22
-------
There are further differences on a micro scale within a landfill. Due
to particle size and composition differences, uneven moisture distribution,
uneven oxygen distribution, uneven nutrient distribution, uneven pH and
redox potential levels from point to point, etc., there will be major dif-
ferences in gas generation from point to point within a landfill at a given
time. Gas measurements are basically macroscopic in nature so the observer
measures total gas generation which is the sum of production from each dif-
ferent pocket of activity within the landfill. Undoubtedly, the relative
importance of methanogenic versus facultative versus aerobic decomposition
pockets is a dynamic situation, changing as waste materials decompose and as
environmental conditions vary on a micro scale.
Moisture content appears to be a major factor affecting methane pro-
duction. Generally, methane formers function better as the moisture con-
tent increases, being very effective when completely submerged in water, as
in a sewage sludge digester. This may be a result of improved uniformity
of composition and reduced variations in nutrient availability, pH, concen-
trations of deleterious substances, etc. Increased moisture content also
limits the accessibility of oxygen, which would poison the methane formation
process if allowed to enter the landfill. Merz found moisture content to be
the most important factor of those he studied affecting gas generation.
Merz and Stone found reduced production of methane in test, pilot scale
landfi-lls of less-Uhan 100 percent dry weight or 50 percent wet weight
moisture content.
The effect of low moisture content in limiting methane formation was
substantiated by Merz and Stone using an enclosed lysimeter. A moisture
content of 50 percent dry weight or 34 percent wet weight was apparently too
low to promote methane formation; whereas, a level of 65 percent dry or 40
percent wet weight was adequate once reasonable temperatures were achieved.
The lack of methane formation at a moisture content of 43 percent dry or 30
percet^ wet weight in a study by Ramaswamy lends credence to this conclu-
sion. It is clear that moisture content is an important factor that can
severely limit or promote methane production, depending on whether it is
less than 50 percent dry weight or approaching 100 percent moisture dry
weight, respectively. In dry climates in particular, this factor may limit
the feasibility of methane extraction unless moisture is added to the refuse
both prior to and during gas production.
Temperature is another major variable affecting methane generation.
Anaerobic sewage sludge digestion is reported to be optimized at 35° C (95°
F), with steadily decreasing levels of activity as the temperature drops to
approximately 10° C at which point little or no methane generation occurs.
Merz and Stone found that the temperature in small test landfills affected
gas production with optimum temperatures also in the 30 to 40° C range.
Since landfill temperatures are often considerably less than 35° C, optimum
conditions for methane formation frequently do not exist, and faculative
micro-organisms will be favored. This affects both the total generation of
methane and gas composition.
Procedural problems in measuring gas composition should also be men-
23
-------
tioned. Air leaks along the walls of gas sampling probes are common pro-
blems allowing rapid contamination of landfill gas by air during gas sam-
pling by suction. Use of clay or concrete seals, for example, reduces the
leakage problem, but leaks through a cracked clay seal if drying takes place,
or leaks around a clay or concrete seal as waste decomposes, settles and
pulls away from the seal can continue to be problems. Settling of a land-
fill and changing moisture conditions at the surface of a landfill can allow
air intrusion through the cover soil during sampling. Permeability of cover
soil to gasof-low varies widely as the moisture content changes or if freez-
ing occurs. The result may be variations in measured gas composition as
a function of precipitation and temperature above the landfill. Further,
changes in barometric pressure have apparently caused variations in gas com-
position, presumably removing landfill gases more rapidly during periods of
low atmospheric pressure and retarding gas venting from a landfill during
high pressure contitions. Additional problems have been caused by the dif-
ficulty in obtaining good impermeable-gas container secants and avoiding
contamination of samples once taken from the landfill. Some, but not all,
gas composition data can be improved by mathematically removing a quantity
of air associated with measured amounts of oxygen, and adjusting the percen-
tage composition of the remaining gas accordingly. However, the difficulty
with this type of correction is that oxygen may be naturally present in the
landfill gas which would make the result erroneous.
Additional variables affecting methane generation were discussed above
and will not be repeated here except to note the uniformity of the levels of
these variables is of major importance. For example, for a landfill with
favorable composition, temperature, and moisture content, the uneven dis-
tribution of decomposable nutrient or toxic substances, uneven distribution
of acidic or basic pH conditions or the local accessibility to oxygen or
other causes of increased redox potential which upset the ability of local
portions of the landfill to sustain methane formation, may affect total me-
thane production. However, adverse moisture content and temperature more
than any other factors are felt to be the major reasons why some landfills
exhibit reduced methane generation.
GAS PRODUCTION RATES AND DURATION OF GAS PRODUCTION
The wide range in types of decomposable matter present in solid waste
suggests that no simple equation or rate constant can describe adequately
the rate of decomposition or the rate of methane generation for a landfill.
Readily decomposable substances like sugars and starches, for example, re-
quire less time to decompose than only moderately decomposable materials such
as cellulose. In order to provide predictive capabilities for the rate of
decomposition, it is useful to consider a landfill as a whole using suffi-
cient measurements to describe the decomposition process, however complex,
and apply the results to new landfills. Such an analysis may be based on
knowledge of the composition characteristics of the various components in a
landfill.
It is generally assumed that biological decomposition proceeds accord-
ing to one of the following three equations:
24
-------
(2) --kc
(3) -£=kc2
where "c" is the concentration of decomposable matter remaining at time "t",
and "k" is a constant. Equation (1) describes a zero order reaction in
which the reaction rate is independent of the concentration of substrate
remaining to be decomposed. It is valid when factors other than substrate
availability limit the rate of decomposition and frequently implies unfa-
vorable or less than optimal conditions. For example, the presence of toxic
substances, the lack of sufficient nutrients, or the lack of moisture may
impede or control the rate of decomposition sufficiently that the concentra-
tion of substance remaining is unimportant. Similarly, so much decomposable
matter may be present that other factors limit biological activity. Zero
order kinetics often describes a transient situation; once the substrate con-
centration is in balance with other decomposition variables, it will become
important. Another situation in which zero order kinetics is observed is
when intermediate stages of decomposition exist, and the concentration of
an interim substance may be controlling the overall reaction rate. In this
case one is modeling the reaction rate on the wrong substrate. In general,
if decomposition proceeds according to zero order kinetics, further investi-
gation is suggested because it may be a result of inadequate understanding
of the process, a serious process imbalance, or poor bacterial growth con-
ditions. In similar fashion, second or higher order reaction rates indi-
cate a major dependence on substrate concentration. Second or higher order
rates imply that growth conditions are favorable, at least for decomposition
of the substrate being modeled, and it is availability of substrate which is
strongly controlling decomposition rates. It may be perfectly acceptable
for the particular reaction being modeled to be of second or even higher or-
der, but it does suggest that further information would be useful to try to
explain the major dependence on substrate concentration.
i
The first order reaction rate is the most common. Simply stated it
means that if the concentration of substrate is halved, its rate of destruc-
tion is also halved. It implies an adequate environment for decomposition
to take place, capable of supporting more or less activity in accordance
with substrate availability. Because of the difficulty in monitoring land-
fill decomposition, there is little evidence that decomposition of landfills
proceeds according to first or any other order kinetic expression. Exper-
ience with other decomposition processes, however, such as anaerobic sewage
sludge digestion, aerobic decomposition of decomposable organics (e.g., the
BOD curve) and the like, indicate that the first order expression is common
and is, therefore, worth attempting with landfills. Substrate concentration
is readily controlled in a sewage sludge digester and the degree of mixing
and presence of adequate water distributes the decomposition activity
throughout the entire vessel. Conversely, with a landfill, pockets of wide-
25
-------
ly differing characteristics promote different types and rates of decomposi-
tion, making it very difficult to apply any kinetic expression except a gross
expression summarizing general observations of the landfill as a whole.
Sampling problems, changing environmental conditions, mixture of substrates,
and the impractical ity of observing a landfill over its entire decomposition
period makes it difficult to develop a more refined model.
Using the first order expression:
^ = -kc
dt kc
and integrating, where c = CQ at t = o:
and defining the half-life as the time "th" at which half of the original
substance has been decomposed:
e"kth = 1/2
or . _ 0.69
*h " ~k~
Therefore, either the half-life or the rate constant "k" is all that must be
specified to describe the decomposition of a material of known initial con-
centration c . Note that "c" may be a concentration of substances to be de-
composed, su8h as organic matter, organic carbon, etc., or it may be a mea-
sure of the decomposition products, such as cubic meters (cubic feet) gas
generated per kilogram (pound) refuse.
Since refuse contains materials of such widely differing characteris-
tic rates of decomposition, it is logical to attempt to consider each in-
dividual component separately, using the first order kinetic expression
and appropriate "k" or "t," values to describe its decomposition independent
of the other components. The total landfill decomposition is then described
by summing the decomposition of all of the components of interest. If one
models gas generation, the expression would be:
c
"
where "G" is the rate of gas generation at time "t", and "j" is the number
of identifiable components whose decomposition results in gas generation.
The constant "k" becomes more complex in this expression because, as written,
it must also include an efficiency term which relates the amount of gas gen-
erated to the amount of each waste component decomposed.
26
-------
Table 3 indicates the typical amounts found of major readily identifi-
able components of refuse. Using these data, the organic portion of munici-
pal wastes can be divided into three categories grossly described as: readi-
ly decomposable, moderately decomposable, and non-decomposable. Food wastes
are readily decomposable, constitute 12 percent of the wet weight of refuse
(Table 3), and in the absence of specific data may be assumed to have a half-
life of one year. This value is reasonable and reflects the non-optimal con-
ditions that exist in a landfill as well as the experiences of those who
have researched refuse decomposition in older landfills in humid climates.
Similarly, paper, wood, grass, brush, greens, and leaves may be considered
moderately decomposable, comprise 57.2 percent of the refuse on a wet weight
basis, and may be assumed to have a half-life of 15 years. Other organic
materials, such as plastics, leather and rubber are assumed to be nondegrad-
able. Using the overall formula for gas generation for each component (pa-
per, grass, fats, etc.) of interest in Table 3, the moderately decomposable
portion will produce ultimately 0.37 std cu m/kg (5.9 std cu ft/lb)
wet refuse which will be 51 percent methane, and the readily decomposable
portion will produce 0.06 std cu m/kg (9.94 std cu ft/lb) wet refuse,
which will be 64 percent methane. These totals can be pro-rated over the
life of the decomposition process using the assumed half-life values and
assuming first order kinetics. Once again, the latter assumption derives
from the common use of the first order equation in sewage sludge digestion
and the lack of any substantive reason to not use it in landfills. The re-
sult is presented in Figures 1 and 2, in which the predicted percent of
non-decomposable matter remaining and the cumulative amount of methane gen-
erated respectively, are shown as functions of time.
In addition to the assumptions and errors associated with use of the
equation for calculating ultimate potential gas generation, discussed pre-
viously, the above simple approach assumes that a first order kinetic ex-
pression is valid, and that the refuse components can be divided into
readily and moderately decomposable fractions with the assumed half-lives.
The generation rate calculated represents a likely maximum value which may
be considerably in error especially in the early years of a landfill decom-
position. One modification of the basic method presented is to assume a rate
of attainment of predominantly methane forming conditions to describe the
early transition of a landfill from aerobic to facultative and finally to
methanogenic decomposition. Such an approach was used by Bowerman. This
reduces the effect of initial portions of the curve of Figure 2 in which
very high methane generation rates are shown to more realistic levels.
There are other ways by which the rate of gas production may be esti-
mated. For example, the shapes of the curves describing gas production with
time ojgasured during digestion of sewage sludge in a 1932 work by Fair and
Moore were used to modify the mathematical expression used in the previous
example. Depicted in Figure 3 is the curve developed by Fair and Moore (ren-
dered dimensionless both with respect to time and rate of gas production)
and assuming half-lives for various components of refuse to provide a time
basis for a gas generation curve describing the subject landfill. They used
existing data on gas generation rate for a known portion of the landfill
over a one year period to set the vertical scale on the gas generation curve
27
-------
00
100
90
80
70
I 60
7
5
: 50
CO
o
css
40
30
o
ID
O
O
o:
Q-
oo
et
C3
20
10
C£
LU
Du
READILY
DECOMPOSABLE
ORGANICS
10
MODERATELY
DECOMPOSABLE
ORGANICS
15
YEARS
20
25
30
35
Figure 1. Theoretical gas production remaining as a function of time.
-------
_ 0.225
3
<*-
* 0.200
1
q-
0
O)
:* 0.175
13
U
o 0.150
0
§
D-
o 0.125
LU
1
h
^ 0.100
o
1-
i 0.075
LU
:»
§
1 0.050
0.025
MAXIMUM = 0.225 cu m/kg
4*
*
^^
^ *
S/'
f
s
/
/
t
/
. /
/
/
.
0 5 10 15 20 25 30 35
YEARS
Figure 2. Theoretical methane production per kilogram of refuse.
29
-------
1.0
0.9 _
0.8
I ' A '
DINENSIONLESS GASIFICATION
CURVE, DEVELOPED FROM
GASIFICATION CURVE BY G. M. FAIR
AND E. W. MOORE.SEWAGE WORKS
JOURNAL MAY 1932
Q = RATE OF GAS PRODUCTION
T = TIME
' 1 1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
T1/Ttotal
Figure 3. Dimensionless gasification curve.
30
-------
mentioned previously. The result was a gas production curve based on the
shape of the Fair and Moore curve for each group of refuse components assumed
to decompose simultaneously. The curves were then summed to give the total
gas generation as a function of time.
The selection of half-lives is little more than a guess based on some
experience with sewage sludge digestion. Values ranging from one-half to
ten years for readily decomposable materials-acid two to 25 years for moder-
ately decomposable materials have been used. ' ltjf" Some investigators as-
sume that refractory materials such as plastics result in no methane forma-
tion; others assumed half-lives as low as 20 years. Climatic conditions
which in turn affect the kinetics of gas formation should be considered in
estimating half-lives in the absence of data.
Table 5 summarizes some of the gas generation rates found in the liter-
ature. Attempts have been made in each case to put the entries on the same
basis to make them comparable, but this is difficult because of conditions
peculiar to each entry. Nevertheless, an idea of typical projected or mea-
sured rates may be obtained from Table 5. Except in the case of cltised
lysimeters, it is clear that gas production figures cannot be based on di-
rect total measurement. Several cases exist, however, in which some degree
of landfill testing was used as a basis of extrapolating the data over the
entire landfill over a longer period of time than was actually monitored, or
both. The term "measured" is used in Table 5 to separate estimates based
on measurements from those based on purely theoretical grounds. Similarly,
values based on literature review involving unknown or no measurements are
listed as "estimated".
Entries 1 through 4 of Table 5 are typical of the purely theoretical
(entry 1) and literature review and experience (entries 2, 3, and 4) ap-
proaches to the rate of gas generation. It is interesting that the theore-
tical result is much closer to a realistic value than the theoretical esti-
mate of total gas production shown in Table 4. Part of this is the choice
of five years after landfill ing as the time at which the generation rate
was calculated from Figure 2 for entry in Table 4. It is clear from the
shape of the curve that much higher or lower rates could have been calculated
had the landfill age been more or less, respectively. However, five years
was selected as being representative of the ages of full-scale landfills
tested. More important, however, is the probability that a landfill is ac-
tually undergoing methanogenic decomposition at this age, thereby following
the theoretical predictions more closely. At earlier ages the theoretical
model overpredicts because of the time necessary to achieve stable methane
formation in an actual landfill. Since significant amounts of gas are pre-
dicted theoretically during the initial years but probably not produced in
reality, part of the discrepancy in total production is explained. No data
are available on gas production from landfills significantly older than 20
years, so comparisons of actual to theoretical rates cannot be made.
Entries 5 through 11 are basically results from enclosed lysimeters or
test landfills. Consequently, measurements of gas production should be rea-
sonable; subject to sampling and analysis difficulties, leaks, and the like.
31
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TABLE 5. LANDFILL GAS (CARBON DIOXIDE AND METHANE) GENERATION RATE FROM MUNICIPAL SOLID HASTE
Sources
Conditions
Basis
Gas production rate
refuse as received
std cu m/kg
GO
1. This report, Figure 2
2. Bowerman, et al (3)
3. SCS Engineers (37)
4, Boyle (13)
5. Merz & Stone (28)
6. Streng (30)
7. Chian & DeWalle (31)
8. Rovers & Farquhar (29)
9. Merz (27)
10. Ramaswamy (10)
11. Beluche (32)
12. Bishop (38)
After 5 years in landfill
Literature and various data sources
Literature and various data sources
Literature
Lysimeter, calculated from 300 days
CH. production
Ave. range during active CH.prod.
for solid waste only lysimeter
Lysimeter gas prod, over 300 days,
recalculated for cell 4*
Lysimeter, maximum production rate
observed
Maximum production in lysimeter at
"optimal" temp, and percent H^O
Lysimeter with unusually high food
waste content
Cited in (25)
Pilot-scale landfill, low H20 content
Theoretical
Estimated
Estimated
Estimated
Measurement
0.016
0.014
0,004 to 0-014
0.004 to 0.014
0.005
Measurement 0.005 to 0.006
Measurement
Measurement
Measurement
Measurement
0.0002
0.008
0.032
0.400
Measurement 0.003
Measurement 0.032 to 0.063
(continued)
-------
TABLE 5 (continued)
Sources
Conditions
Basis
Gas production rate
refuse as received
std cu m/kg
13. Engineering Science (39) Test landfill, maximum and minimum Measurement 0.016 to 0.041
observed production on per year
basis over 3-years monitoring
14. Carlson, E.L. (35)
15. Carlson, J.A. (2)
Estimated during landfill pump tests, Measurement 0.004 to 0.039
varies seasonally
Estimated during landfill pump tests, Measurement 0.021 to 0.029
both values given
co
CO
16. City of Los Angeles (25) Theoretical extrapolation of short- Measurement/
term landfill pumping data Theoretical
17. City of Glendale (40)
Testing of landfill, recalculated
for 53 percent CH,
Measurement
0.011
0.002
* Corrected to refuse composition of Table 3.
-------
It is very difficult, however, to achieve realistic conditions in a test
landfill as mentioned previously. Moisture routing is one particularly dif-
ficult aspect to model of a full-scale landfill. Entries 6, 7, and 8 ex-
perienced difficulties attaining methane formation and traced problems to
moisture, temperature, air leaks, and acidic pH conditions. In some cases,
methane formation was never achieved and in others low levels were observed.
More time might have allowed methane formation to develop in some of these
cases. At any rate, the rates of production for many of these entries are
likely to be unrealistically low. Similarly, entry 10 is abnormally high
because of a waste artificially high in methane formation potential. Entries
5 and 9 indicate the effect of moisture content with higher production rates
associated with wetter landfills.
Entries 12 and 13 are on pilot-scale landfills and are thought to be
reasonable results for young, actively decomposing landfills.
Entries 14 through 17 are for full-scale landfills. The typical ap-
proach for such studies is to pump gas out of a perforated pipe placed in
a well in the landfill which is backfilled with gravel. The well hole is
typically 0.91 to 1.22 m (36 to 48 in.) in diameter. The area of influence
of each gas withdrawal well is then determined by pumping the gases and
monitoring changes in pressure at a series of test probes located at various
distances from the withdrawal well. The test probes are basically pipes,
perforated along the bottom several feet, embedded in the landfill to allow
measurement of pressure. While it is possible to measure with reasonable
accuracy the rate of gas withdrawal and its composition, it is much more dif-
ficult to define the radius of influence so that the gas production can be
related to the correct volume of refuse. Consequently, the production rates
given in these entries are subject to errors in tonnage of refuse generating
gas measured, gas losses to other parts of the landfill or through cover or
surrounding soils, and whether the value applies to only that portion of the
landfill tested at that time. Entry 16 is especially interesting, because
the value is based on a year of pumping from a series of withdrawal wells.
The values given in Table 5 suggest that both from test and full-scale
landfill data, a reasonable rate of total gas generation is 0.006 to 0.038
std cu m/kg/yr (0.1 to 0.6 std cu ft/lb/yr) for refuse as received.
The range is explained in part by seasonal or climatic variations relating
primarily to moisture content and to a lesser extent, temperature varia-
tions. Values outside this range are generally explainable by unusual re-
fuse composition, lack of formation of a mature methanogenic decomposition
process, or very dry refuse.
The period over which methane is produced is unknown. Theoretically,
decomposable matter will degrade in a landfill for an infinite period, but
obviously a point will be reached in practice when so little decomposition
takes place that methane production effectively ceases. At this point,
facultative biological, chemical and physical decomposition as well as some
traces of methanogenic decomposition, will continue at some low level until
the refuse is, for all practical purposes fully decomposed. All of the stu-
dies cited in Table 5 cover such a short period of time that little can be
34
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said regarding the period of methane production. Several of the lysimeter
and test landfill studies did apparently extend over the period of active
methane production rates or were declining or had stopped altogether by the
end of the monitoring period. Such studies, however, are probably not re-
presentative of full-scale landfills where methane generation appears to
occur over periods much longer than those monitored for the lysimeter or
test landfill studies. Those entries which project methane production over
a period of time (e.g., entries 2, 15, 16, and 17) generally assume a period
of active methane production on the order of ten years (at rates warranting
collection).
Factors affecting gas generation rates (as opposed to total production
per unit weight of refuse) have been clearly identified in the literature
although in some particular test landfills or lysimeters, the effects of
these factors are obscured by other factors which were apparently control-
ling. The effect of temperature has been shown in several studies and is
summarized in reference 36. The optimum temperature range for mesophilic
anaerobic bacteria is 30 to 40° C which has been observed to give maximum
gas production rates. Moisture content is apparently the major variable
affecting gas production rates, assuming that reasonable environmental con-
ditions supportive of methane formation exist. Reference 36 also summarizes
data from several sources indicating a general improvement in gas produc-
tion with increasing moisture content ranging up to complete water submersion
in refuse digestors. Moisture content significantly less than 50 percent on
a dry weight basis (34 percent wet weight) may limit gas production. How-
ever, there is considerable uncertainty on this value because landfills with
measured moisture content as low as 15 to 20 percent (wet weight basis) are
producing methane at relatively high rates. Certainly, higher moisture con-
tent will sustain higher gas production rates but other variables i(jingeneral
and temperature in particular then play an increasingly major role. '
SUMMARY
Gas production in decomposing landfills is complex, involving availabil-
ity of balanced supplies of decomposable solid waste components plus satis-
faction of stringent environmental requirements to promote growth of methane
forming bacteria. Non-methanogenic decomposition processes, favored initial-
ly upon refuse placement in a landfill and during subsequent years when en-
vironmental factors upset stable methane formation, make it.difficult to
predict accurately methane production quantities and rates. Knowledge of
the specific requirements of methane formers exists, however, and has been
used successfully to interpret available gas production data. Such knowledge
stems primarily from experience with sewage sludge digestion.
The theoretical amount of gas generated from typical residential/com-
mercial/and light industrial solid waste is 0.45 std cu m/kJ (7.2 std cu
ft/lb) of wet (as received) waste. It would have a composition of 54 per-
cent methane and 46 percent carbon dioxide by volume. Based on lysimeter
and full-scale landfill tests, however, a value of 0.013 to 0.047 std cu m
(0.2 to 0.75 std cu ft) of methane/kg (Ib) is more realistic. The rate
of methane generation is also subject to considerable errors in estimation,
35
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with a reasonable theoretical value of 0.008 std cu m (0.13 std cu ft)
of methane/kg (Ib) of refuse per year after five years in a landfill
Averaging the results of lysimeter and full-scale landfill measurements,
total gas generation is in the range of 0.006 to 0.038 std cu m/kg/yr
(0 1 to 0.6 std cu ft/lb/yr) over the period of most active methane
formation, which is typically assumed to occur during the first five years
or so after landfilling. It is difficult to reconcile these results with
the beliefs of many researchers that the economically productive period of
a landfill may last anywhere from 15 to 25 years.
Factors which appear to regulate methane generation most often are
moisture content and temperature. A refuse moisture content on the order
of 50 percent on a dry weight basis and preferably 100 percent (34 and 50
percent wet weight) is required for active methane generation. Likewise, a
temperature of less than 15° C (59° F) appears to severely limit methane
generation with the rate of generation increasing with increasing tempera-
tures up to an optimal temperature of 30 to 40° C (86 to 104° F). It is
likely that sub-optimal temperature and moisture levels are the most common
causes of retarded methane generation in full-scale landfills. Since me-
thane is routinely found in decomposing landfills, sub-optimal conditions
seldom preclude all traces of methane formation. Rather, when such condi-
tions exist they serve to limit the rate of generation and so might con-
ceivably be controlled to speed up the generation process.
36
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SECTION 5
LANDFILL GAS UTILIZATION ALTERNATIVES
Possible uses for landfill gas are presented in this section, together
with technical and economic analyses of process systems required to prepare
the landfill (methane) gas for use. The analyses are based on landfill gas
of typical composition, although it must be noted that gas composition varies
somewhat depending on the composition of the solid waste, the age or maturi-
ty of the landfill and other factors.
Each economic analysis determined the approximate gas quantity required
to render each alternative economically viable. The assessment considered
the number of years required to "payback" the original capital investment,
mindful of the number of years that a typical landfill can be expected to
produce gas at a rate sufficient to permit economical recovery.
LANDFILL GAS COMPOSITION
Landfill decomposition gases are comprised almost entirely of methane
and carbon dioxide in about a 1:1 ratio. The ratio of methane to carbon
dioxode varies somewhat due to the type, age, condition and mix of organic
components present. However, gas composition tends to remain relatively
constant during the useful period of gas production varying slightly from
landfill to landfill and over time.
Nitrogen and oxygen are normally the next most abundant constituents in
landfill gas. These gases occur primarily as a result of air being trapped
as the waste is deposited or suction due to negative internal pressure as
the landfill gas is extracted. The latter is minimized with proper well
design, gas extraction and selection of landfill cover material. Because
oxygen can be consumed within the landfill by faculative or aerobic bacteria
or in chemical reactions with materials present (e.g., metals), the ratio
of nitrogen to oxygen will not always be 4:1 and it is not possible to iden-
tify that portion of the nitrogen or oxygen in a sample that is due to in-
gested air and that portion that is part of the gas produced. In samples
taken using techniques that virtually eliminate the possibility of air in-
gestion, nitrogen is present in more than trace amounts. The production of
nitrogen conceivably could occur as a result of waste decomposition, since
a small amount of nitrogen generally is present in typiqal landfill gas.
Of the many substances that are found in landfill gas in concentrations
less than 1 percent, hydrogen, hydrogen sulfide, carbon monoxide and higher-
order hydrocarbons are the most abundant. Although these compounds normal-
37
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ly comprise only a few hundred parts per million (ppm), some analyses show
them occurring as several thousand ppm (one thousand ppm is equal to 0.1
percent volume). Hydrogen sulfide, because of its unpleasant odor in gase-
ous form, toxicity, and corrosiveness when dissolved in water (sulfuric acid)
is the most troublesome of these compounds.
Trace amounts (1 to 50 ppm) of numerous additional compounds have been
reported in gas analyses performed by mass spectroscopy. These include sul-
fur dioxide, benzene, toluene, perch!oroethylene, methyl chloride, and car-
bony! sulfide. In addition, the moisture in the gas (most collected land-
fill gases are saturated or near saturation) has been found to contain drop-
lets of numerous organic acids (carbonic, acetic, propionic, isobutyric,
isovaleric, isocaproic, and others), ammonia and other less important com-
pounds in trace quantities (less than 1.06 mg/cu m). Some of these com-
pounds are of concern due to their corrosiveness, or tendency to plug up
process equipment or interfere with process activities.
To provide the greatest applicability for the results of this study,
a landfill gas that contained each of the compounds in the upper range of
concentrations found was used for analysis purposes. This makes the results
somewhat conservative because in most of the gas analyses reviewed, only a
few of these compounds were found and their concentrations were near the
lower end of the ranges. Thus, cost estimates affected by corrosion control
requirements or similar measures needed to control adverse affects of these
compounds tend to be overstated with respect to most landfill gases. A
certain amount of air intrusion due to leaks in typical gas recovery systems
was assumed, giving methane percentages resulting in a higher heating value
(HHV) of 18289 kJ/std cu m (490 BTU/scf). A more conservative figure of
17727 kJ/std cu m (475 BTU/scf) has been used in subsequent calculations.
Typical gas composition used in this study is listed in Table 6.
ALTERNATIVE LANDFILL GAS USES
Based on the typical landfill gas composition listed in Table 7, poten-
tial uses are of two basic types:
o Use as a fuel gas at various quality levels
o Use as a process feed stock
Table 7 lists alternative applications of landfill gas as a fuel at
various quality levels.
Conversion of methanol is a representative process using landfill gas
as the feed stock. Other potential conversion products include ammonia and
urea. However, methanol conversion is perhaps the most feasible of the
three possibilities mentioned. More suitable feed stocks are available in
relatively larger quantities such that considering the economies of scale,
use of landfill gas as a feed stock from a single site would have basic cost
disadvantages. The methanol process is treated in the economic analysis to
38
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TABLE 6. TYPICAL LANDFILL GAS COMPOSITION AND CHARACTERISTICS
Component percent
Component (dry volume basis)
Methane 47.5
Carbon Dioxide 47.0
Nitrogen 3.7
Oxygen 0!s
Paraffin Hydrocarbons 0.1
Aromatic & Cylic Hydrocarbons 0.2
Hydrogen 0.1
Hydrogen Sulfide 0.01
Carbon Monoxide 0.1
Trace compounds* 0.5
Characteristic Value
Temperature (at source) 41 °C
High heating value 17727 kJ/std cu mt
Specific gravity 1.04
Moisture content Saturated (trace
compounds in
moisture)!
* Trace compounds include sulfur dioxide, benzene, toluene, methylene
chloride, perchlorethylene, and carbonyl sulfide in concentrations up
to 50 ppm.
t Landfill gas (as received) from Palos Verdes landfill has HHV of 21646
to 21832 kJ/std cu m (3). Landfill gas (as received) from a Mountain
View landfill test well has a HHV of 16420 to 16794 kJ/std cu m with a
20-21 percent nitrogen content by volume (1,2).
I Trace compounds include organic acids(7.06 mg/cu m) and ammonia (0.71
mg/cu m).
39
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TABLE 7. ALTERNATIVE LANDFILL GAS FUEL APPLICATIONS
Application
Processing Higher heating value(HHV)*
required kJ/std cu m (BTU/scf)
Limitations
Direct Fuel
Direct Fuel
Direct Fuel
Direct Fuel
Direct Fuel
Direct Fuel
Condensate &
particulate
removal
Dehydration
Dehydration &
partial carbon
dioxide removal
Dehydration &
total carbon
dioxide removal
17167 to 18287
(460 to 490)
17167 to 18287
(460 to 490)
24258 to 27990
(650 to 750)
35080 to 35827
(940 to 960)
Dehydration, car- 35827 to 36947
bon dioxide & ni- (960 to 990)t
trogen removal
Dehydration & car- 37320+
bon dioxide remo- (1,000+)
val plus sweetening
with approximately
1 percent propane
Must be consumed
at the landfill
Can be trans-
ported via pipe-
line moderate
distances
can be trans-
ported moderate
distances and
mixed with na-
tural gas at low
ratios
Can be mixed with
natural gas at
intermediate to
high ratios
Can be mixed with
natural gas at
intermediate to
high ratios
Equivalent to
natural gas
* 1 percent other hydrocarbons add about 1120 kJ/std cu m (30 BTU/scf) to
HHV.
t Palos Verdes landfill molecular sieve product, during 204 days of opera-
tion, averaged 99 percent methane, HHV 36947 kJ/std cu m (990 BTU/scf) (3)
40
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demonstrate this contention.
Direct fuel application with partial carbon dioxide removal offers no
distinct advantage over use of gas that has only been dehydrated. The cost
of removing all carbon dioxide is not that much greater than that of remov-
ing only about one-half. Also, for introduction into the natural gas distri-
bution system, most utilities require a gas with a heating value of about
35454 kJ/std cu m (950 BTU/scf), so a gas with only part of the carbon
dioxide removed cannot be used for this purpose. For these reasons, con-
sideration of partial carbon dioxide removal was not carried further in the
analysis. (Note that unique circumstances can render this approach fea-
sible.)
Raw landfill gas can be consumed on or immediately adjacent to the
landfill site to generate steam for process or heating use, or to generate
electricity via a gas engine, gas turbine or steam turbine as the prime mo-
ver. The advantage of on-site utilization is that little or no processing
is required. The gas can be used as a medium heating value fuel directly
after passing through a condensate and particulate separator. These two
raw gas utilizations are analyzed in greater detail.
ALTERNATIVE PROCESSES AND PRODUCTS
The most suitable utilization of gas from a given landfill site depends
upon the quality of the raw gas recovered (primarily methane content and
amount of nitrogen and oxygen), the demand for energy near the site and the
quantity of gas recovered. Based on demonstration projects and the few ad-
ditional commercial operations now in late stages of development, industry
will purchase substandard fuel gas provided it does not damage existing
facilities (pipelines, boilers and furnaces, etc.), or, if there is a need
for low to medium pressure/temperature steam. Under some circumstances,
industry also will purchase electricity. However, if there are no large
industrial or institutional users of fuel gas, steam, or electricity near
the landfill site, it probably will be necessary to sell upgraded gas or
electricity generated on-site to the local utility. (In unusual cases, the
only suitable alternative may be synthesis of methanol, ammonia or urea.
However, the economics of these processes tend to require large landfill
gas recovery rates in order for the facility to turn a profit.)
To cover the range of potential uses or products feasible under a vari-
ety of situations, representative alternative processes producing specific
products were selected for analysis. The selection was based on current
state-of-the-art and minimal technical risk processes. It was recognized
that for some products (e.g., dehydrated and upgraded landfill gas) there are
a variety of process techniques and adsorbant materials available. Thus, for
example, use of substances such as mono-ethanol-amine (MEA) may be substi-
tuted for the molecular sieve technique to remove carbon dioxide in Alter-
natives II, III, and IV. The selections made were considered representative
of the range of product qualities and processes attainable at this time.
The alternatives analyzed were:
41
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I. Dehydration (dehydrate, compress and sell 17727 kJ/std cu m (475
BTU/scf) gas)
II. Upgrading (remove water and carbon dioxide, compress and sell 35454
kJ/std cu m (950 BTU/scf) gas).
III. Upgrading (remove water, carbon dioxide and nitrogen, compress and
sell 36387 kJ/std cu m (975 BTU/scf) gas).
IV Upgrading and Blending (remove water and carbon dioxide, add about
1 percent propane and sell 37320 kJ/std cu m (1000 BTU/scf) gas).
V. Steam generation (use raw gas to generate steam and sell steam)
VI. Electricity Generation (use raw gas to generate steam to drive
steam turbine-generator and sell electricity)
VII. Electricity Generation (use raw gas in gas turbine-generator and
sell electricity)
VIII. Electricity Generation (use raw gas in gas engine-generator and sell
electricity)
IX. Methanol Synthesis (remove water and carbon dioxide, reform and con-
vert to methanol, sell methanol)
Each alternative is briefly described using a simplified process sche-
matic diagram. The following assumptions were used in evaluating each al-
ternative:
1. Raw gas must be consumed on-site because moisture prevents pipeline
transport
2. Dehydrated gas is supplied to large fuel gas users within approxi-
mately 8 km (5 miles) of the site
3. Steam is supplied to large users within 1.6 km (1 mile) of the site
4. Electricity is sold to one or a few users, or is synchronized and
sold to the local electric power utility
5. Upgraded gas is sold to the local gas utility and methanol is sold
to large users locally
Three alternative methods for generation of electricity were analyzed
because it was anticipated that their economics as functions of capacity
would be different, thus different methods might be applicable to small,
medium and large gas quantities. The propane blending upgrade process was
explored as a substitute for nitrogen removal via liquification which tends
to be an expensive process.
42
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Alternative I - Dehydration to Product 17727 kJ/std cu m (475 BTU/scf)
Dry Gas
This is a basic process to remove water vapor from landfill gas for
short to medium distance transport by pipeline to single or multiple fuel
gas users. The raw landfill gas is recovered using the suction of the
compressor(s) applied to the collection manifold. As shown in Figure 4, raw
(as-recovered) gas is passed through a liquid-solids separator to remove
condensate and any particulates present, then is compressed in a low pres-
sure compressor followed by two stages of cooling and a condensate separ -
tor, and then to a tri-ethylene-glycol dehydrator before passing to a de-
livery pipeline or to a second compression stage (not shown) depending upon
pipeline length and user delivery pressure requirements. Rich glycol is
circulated through a reboiler where the water is vaporized and the lean gly-
col recirculated and reused. The flare unit is normally used to destroy
vapors eminating from the glycol reboiler and in an emergency situation, to
flare the landfill gas.
Refrigeration dehydration can be substituted for the glycol unit for
small gas quantities. The ratio of delivered gas to recovered gas ranges
from 0.95 for low pressure, 153 kN/sq m (22.5 psig) delivery, using elec-
tric motor driven compressors to about 0.83 for medium pressure, 448 kN/sq
m (65 psig) delivery, using gas engine driven compressors.
Alternative II - Upgrading to 35454 kJ/std cu m (950 BTU/scf) Gas
Depicted in Figure 5 is a basic landfill gas upgrading process incor-
porating removal of carbon dioxide as well as water vapor to achieve a dry
gas heating value ranging from about 35080 to, 35827 kJ/std cu m (940 to
960 BTU/scf) depending upon raw gas heating value (methane and other hydro-
carbon content) and amount of carbon dioxide and nitrogen in the gas toge-
ther with the effectiveness of the removal technique. Several carbon di-
oxide removal techniques are available including molecular sieve adsorption;
or mono-ethanol-amine, hot potassium carbonate or polyethylene glycol water
absorption. Based on data available on these alternative techniques, the
molecular sieve was selected for analysis because it appeared to be the most
economic. With this alternative, it is important not to over-pump the land-
fill since that increases the nitrogen content and reduces the heating value
of the product. Nitrogen is not removed by these techniques and may de-
crease carbon dioxide removal effectiveness as well. Upgraded gas produced
by molecular sieve separation normally would be suitable for commingling
with natural gas at a reasonable ratio. For example a mix of 10 percent
upgraded landfill gas with 90 percent 37320 kJ/std cu m (1000 BTU/scf)
natural gas gives a mixed heating value of 37133 kJ/std cu m (995 BTU/
scf), or a 2 percent mix results in a reduction of only 37.32 kJ/std cu m
(1 BTU/scf) in heating value.
Two or three stages of compression are typically required before the
upgraded gas can be introduced into the local utility natural gas main.
Approximately 62 percent of the heating value of the input raw landfill gas
will be contained in the output upgraded gas, the difference being used or
43
-------
CJ3
LIQUID-SOLIDS
SEPARATOR
CONDENSATE
SEPARATOR
137.9 kN/nT
TO DELIVERY
PIPELINE
WATER
DRAIN
DESIGNED
TO OPERATE
UNDER
VACUUM
( r-H '
' / U|iJ
ONE OR MORE
COMPRESSOR
UNITS (ELEC-
TRICITY OR
GAS ENGINE
DRIVEN)
WATER
CIRCULATION
PUMP
WATER
CONDENSATE
(C02 ACIDI
SURPLUS GAS
TO EMERGENCY
FLARE
PRODUCT 17727 kJ/std cu m DRY GAS
DEMISTER
GLYCOL
CONTACTOR
ABSORBED
VAPORS
;)
L_^ 1
WATER
DRAIN \s
SFA1
\f
t.
L
|
I
\
a
I
GLYCOL
REBOILER
J-O
Fl
_>.
GAS
FUEL
O3
FLAME
ARRESTOR
Figure 4. Alternative I - Dehydration to dry fuel gas.
-------
01
LIQUID-
SOLIDS
SEPARATOR
WATER
DRAIN
RECYCLE GAS
DEHYDRATION AND
H2S REMOVAL UNIT
GAS
COOLER
HIGH C09 CONTENT
VENT GAS
TWO STAGES OF
COMPRESSION
FLAME
ARRESTOR
. 43:
re
FLARE
FLAME
ARRESTOR
DRAIN WATER
AND LIQUID
HYDROCARBONS
'PILOT GAS
GAS FUEL TO DELIVERY
PIPELINE OR UTILITY MAIN
THIRD STAGE
COMPRESSOR
35454 kJ/std cu m
CARBON DIOXIDE REMOVAL UNITS
(MOLECULAR SIEVES, CYCLIC
SEQUENTIAL OPERATION, AUTOMATIC-
TIMED, HEATING AND COOLING UNITS
REQUIRED)
GAS TO EMERGENCY FLARE
Figure 5. Alternative II - Upgrading to 35454 kJ/std cu m fuel gas.
-------
lost in the upgrading process. Because of this energy loss, this alterna-
tive should be used only when there is no large fuel gas user in the vici-
nity of the landfill and the product gas must be sold to the local gas
utility.
Alternative III - Upgrading to 36387 kJ/std cu m (975 BTU/scf) Gas
This alternative employs the same techniques used in Alternative II with
the addition of nitrogen removal fractional liquification using mechanical
refrigeration. This process liquifies the methane component of the gas
leaving nitrogen and other impurities to be exhausted in gaseous form.
Generally, it would be appropriate only when the nitrogen content of raw
landfill gas is unusually high due to air intrusion into the landfill or
extraction system. It requires considerable additional equipment for the
liquification process and substantially increases the operating cost due to
the high energy requirement of mechanical refrigeration. The basic process
schematic is shown in Figure 6. Only about 54 percent of the energy content
of the raw landfill gas is delivered in the methane product, the differ-
ence being used or lost in the total process.
Alternative IV - Upgrading and Blending with Propane
This alternative was explored as a substitute for Alternative III for
applications where high BTU gas is required, essentially equivalent to
natural gas or nearly pure methane. The schematic in Figure 7 shows only
the process required to be added to the system of Alternative II which pro-
vides dehydration and carbon dioxide removal from raw landfill gas The
blending of approximately 1 percent of propane to 35454 kJ/std cu m (950
BTU/scf) product of the initial two steps of the process increases the heat-
ing value to 37320 kJ/std cu m (1000 BTU/scf). Blending additional pro-
pane could increase the heating value further should this be necessary. The
ratio of heating value in the product gas is the same as for Alternative II
plus the propane added.
Alternative V - Steam Generation
This alternative depicted schematically in figure 8, utilizes an on-
site boiler to generate low or medium pressure/temperature steam (ranging
from 120°C (250°F) saturated to about 260°C (500°F), 3448 kN/sq m (500
psig) superheated steam) burning raw landfill gas that has passed through a
liquid-solids separator and low pressure compressor. The compressor is used
to apply a negative pressure to the collection manifold and for supplying
landfill gas to the boiler burners at a pressure ranging from 34 to 69 kN/
sq m (5 to 10 psig). To achieve maximum economy in water use, a condensate
return line as well as an insulated steam delivery pipeline is needed be-
tween the boiler and the steam purchaser. Because of the high cost of a
high pressure, steel, insulated pipeline and the heat loss involved, normal-
ly the distance between the landfill and steam purchaser is limited to 1.6
km (1 mile), and preferably less. Ratio of gas used to generate steam to
gas recovered will range from 0.92 to 0.96 and boiler conversion efficiency
should be in the range of 75 to 85 percent. Because the boiler is located
46
-------
RECYCLE GAS
LIQUID-SOLIpS
SEPARATOR
T|,<- DEHYDF
ij:> H2S RE
GAS P
__ COOLER ^
WI
IMOV
1
ON
AL
M
AND
UNIT
HIGH CO,
VENT GAS
fl
f?
CONTENT
s~\ /-
A (/
TWO STAGES OF
COMPRESSION
WATER
DRAIN
FLAME
ARRESTOR
FLARE
PILOT GAS
K
REFRIGERATION
UNIT (PARTIAL
CONDENSER)
METHANE
CONDENSATE
RECTIFIER
CARBON DIOXIDE REMOVAL 'UNITS
COMPRESSOR
FINAL HEAT
EXCHANGER
PRIMARY
HEAT
EXCHANGER
NITROGEN CONCENTRATED
US IU HAKt
FLAME
ARRESTOR
GAS FUEL TO
DELIVERY PIPE-
LINE OR UTILITY
Figure 6. Alternative III - Upgrading to 36387 kJ/std cu m fuel gas.
-------
00
35454 kJ/std cu m
GAS FROM DEHYDRATION
AND C09 REMOVAL
PROCESSES
PROPORTIONAL
FLOW METERS
SAFETY
VALVE £
i
(
s~
1
t
EXCESS
FLOW RECYCLE
pixj
)
1 w c1
^A C,
1
. I
r-
"~NN
rJ
fl
t-ftJ-j
^TJ
WflDT/
VAKlr
PROP/
TEMPERATURE
CONTROLLED HEAT
NPUT
PROPANE VAPORIZER
GAS TO DELIVERY PIPELINE
OR UTILITY MAIN
CALORIMETER
PROPANE STORAGE
Figure 7. Alternative IV - Upgrading and propane blending to 37320 kJ/std cu m gas.
-------
WATER DRAIN
FEED WATER HEATER
AND DEAERATOR
BOILER
LIQUID-SOLIDS
SEPARATOR
MANUAL
WATER
DRAIN
GAS TO EMERGENCY FLARE
STEAM CON-
DENSATE FROM
USER
FLARE
FLAME
ARRESTOR
Figure 8. Alternative V - Low or medium pressure/temperature steam generation.
-------
on-site, dehydration is unnecessary although provisions must be made in the
on-site landfill gas pipeline to drain water and the pipeline must be cor-
rosion resistant (constructed of plastic material such as PVC).
Alternative VI - Electricity Generation, Steam Turbine
Shown in Figure 9, this alternative uses the same system as Alternative
V to generate medium pressure/temperature steam that is then supplied to a
steam turbine-generator to generate electricity. As in Alternative V, the
only processing applied to the raw landfill gas is to separate condensed
water and any entrapped particulates followed by low pressure, 34 to 69 kN/
sq m (5 to 10 psig) compression to deliver the gas to the boiler burners.
Electricity is transformed to appropriate voltage for transmission to one
or more ultimate users or to the local utility after the current has been
synchronized with the power supply.
Alternative VII - Electricity Generation, Gas Turbine
For this alternative, raw landfill gas from which the condensate and
particulates have been removed, is compressed in a three stage compressor
to about 1379 kN/sq m (200 psig). It is cooled and additional condensate
removed before being fed to one or more gas turbine-generator sets. This
alternative is based on presently available industrial gas turbines or those
expected to be available in one or two years. As can be observed from the
schematic in Figure 10, this electricity generation system is somewhat
simpler than that required for a steam turbine since it avoids the interme-
diate transformation to steam. Ratio of landfill gas delivered to the gas
turbine to energy recovered will range from about 0.82 to 0.87 primarily
due to the gas consumed by the gas engine driven compressors. If the gas
turbines are used to drive the compressors through a suitable gear box,
capital costs may be reduced somewhat but an equivalent amount of turbine
shaft horsepower will be used. The net power available for delivery will
thus be about the same as for the system employing gas engine driven com-
pressors.
Alternative VIII - Electricity Generation, Gas Engine
This alternative is similar to Alternative VII although somewhat sim-
pler in requiring only low pressure compression, 34 to 69 kN/sq m (5 to 10
psig) for delivery to the gas engine prime mover. Raw landfill gas is
passed through a liquid-solids separator enroute to the compressor that de-
livers the gas to the gas engine, a heavy duty, low speed, spark ignition
type otto cycle engine. For this analysis, single and multiple 2.34 MM kJ
(650 kw) gas engine-generator sets were used, although lower capacity sets
are available. Ratio of gas delivered to the engine to that recovered will
be in the 0.92 to 0.96 range. Equipment costs for gas engine driven genera-
tor sets are less than for steam turbine or gas turbine sets, but mainte-
nance on the reciprocating engine can be expected to be considerably greater
than for the purely rotational turbines. Figure 11 demonstrates the rela-
tive simplicity of this alternative.
50
-------
FEED WATER HEATER
AND DEAERATOR
BOILER
LIQUID-SOLIDS
SEPARATOR
WATER
DRAIN
MANUAL
STEAM
CONDENSER
WHI LK
DRAIN
"O
(VACUUM;
CONDENSATE
1
FLAME
ELECTRICITY TO
USER OR UTILITY
FLARE
Figure 9. Alternative IV - Electricity generation (steam turbine).
-------
LIQUID-SOLIDS
SEPARATOR
01
ro
WATER
DRAIN
WATER
ELECTRICITY TO USER
OR UTILITY
INTERCOOLERS|
AND
SEPARATORS
WATER
THREE STAGES OF
COMPRESSION/
INTERCOOLING BUT
NO THIRD STAGE
AFTER COOLING
HIGH BTU (PROPANE OR
METHANE) FUEL FOR STARTUP
OIL AMD
CONDENSATE
GAS TO EMERGENCY FLARE
FLAME
.ARRESTOR
FLARE
Figure 10. Alternative VII - Electricity generation (gas turbine).
-------
ELECTRICITY TO
USER OR UTILITY
01
CO
LIQUID-SOLIDS
SEPARATOR
WATER
DRAIN
HIGH BTU (PROPANE OR
METHANE) FUEL FOR STARTING
OR "SWEETENING"
GAS TO EMERGENCY FLARE
ELECTRIC
GENERATOR
FLAME
ARRESTOR
SWITCH
GEAR AND
SYNCHRONIZE
FLARE
Figure 11. Alternative VIII - Electricity generation (gas engine).
-------
Alternative IX - Methanol Synthesis
Noted earlier, methanol synthesis was selected as representative of use
of upgraded landfill gas as a feed stock for conversion to another com-
pound; it is probably the most cost-effective of three possibilities;
methanol, ammonia and urea. Figure 12 shows in simplified form the basic
schematic for this alternative. To convert high methane content gas to
methanol requires the addition of high pressure compression, reforming and
catalytic conversion following the dehydration and carbon dioxide removal
steps of Alternative II. Because of the high pressure and gas purity re-
quired for the conversion (to avoid poisoning the catalyst), conversion to
methanol tends to be an expensive process and one that results in about a
67 percent loss of available energy. It is presented to demonstrate the
basic economics of using upgraded landfill gas as a chemical feed stock.
COST AND ECONOMICS OF ALTERNATIVE LANDFILL GAS UITLIZATIONS
In order to develop economic comparisons of alternative landfill gas
uses, showing the economic relationships for various gas recovery quan-
tities and processes for each product,the following standardized product
values were used.
Product
Dehydrated LFG
Steam
Electricity
Electricity
Upgraded LFG
Methanol
Purchaser
Industrial or institutional
Industrial or institutional
Industrial or institutional
Utility
Utility
Industrial
Value
Retail natural gas (N.
G.) price $2.00/1.05
MM kJ (MM BTUs)
Gas used to generate
steam - $2.00/1.05 MM
kJ (MM BTUs)
Retail price $0.05/
kw-hr
Wholesale price $0.03/
kw-hr
Wholesale N.G. price
$1.65/1.05 MM kJ
$0.092/L ($0.35/gal)
For cost estimating purposes, standardized investment capital loan
interest rates were used as follows:
LFG Recovery Subsystem
Process Subsystem
10 year amortization at 8.5 percent
annual interest
20 year amortization at 8.5 percent
annual interest
54
-------
en
01
UNCONDENSED VAPORS TO FLARE
PRIMARY
PURIFICATION
BED
LIQUID-SOLID!
SEPARATOR
MAIN COMPRESSOR
STEAM
TO TURBINE
RECYCLE
VAPORS TO,
TURBINE
txj
INVERTER
:ATALYST
KKKUA.
/m DIS.-U
CHARGE
E
,
1
f '
V
HEAT
RECOVERY
UNIT
LOW BTU
FUEL GAS
TO TANK TRUCK
OR TANK CAR
PURFIED
METHANOL
STORAGE
METHANOL
PURIFICATION
UNITS
(DISTILLATIC
N)
T
Figure 12. Alternative IX - Methanol synthesis.
METHANOL
SEPARATOR
-------
Delivery Pipeline 10 year amortization at 8.5 percent
annual interest
A shorter amortization period was used for the recovery and delivery
subsystems because of the uncertainties in the period in which a mature
landfill can be expected to produce gas at a rate sufficient to warrant
recovery, processing and sale. However, major process equipment normally
has a useful life of at least 20 years, and frequently more with proper
maintenance, overhaul and parts replacement. The assumption is that after
about ten or more years the landfill gas generation rate may be reduced to
the point that recovery becomes uneconomical, thus the recovery system and
pipeline cost must be amortized over that period. In contrast, however,
the process system could be moved to another site and used for at least an
additional ten years or sold at about one-half replacement value to another
operator.
The number of system operating days per year are based on the type of
system and equipment involved. Even though the demand characteristics of
most industrial users are from 8 to 24 hours per day, and from five to
seven days per week, such that there could be significant number of non-
delivery hours or days per month, gas delivery rates can be increased over
the average recovery rate based on a continuous operating cycle using the
landfill as the short term storage vessel. Stoppages during normal delivery
periods are allowed for in the number of annual days of plant operation
estimated to be between 330 to 350 days per year for all but methanol syn-
thesis which is assigned 300 days per year.
Material, equipment and construction cost estimates are based on late
1977.and early 1978 prices and all economic analysis was conducted in cur-
rent, 1978 dollars. Because of broad variations in local conditions, costs
of land, construction loan interest and working capital are not included
in the economic analysis. Also, since the ratio of equity to loan capital
varies widely, the assumption is that return on equity capital will be equal
to the equity to loan capital ratio. Because of similar broad variations,
income taxes and local property taxes are not included. Thus profit and
return on investment are computed before all applicable taxes are deducted.
Representative gross returns on investment (ROI) are used to estimate daily
landfill gas (LFG) recovery quantities necessary for system economic via-
bility.
Operating costs include interest and amortization for each of the three
subsystems: recovery, processing and delivery, based on a standard 8.5
percent interest rate, with amortization periods of ten years for recovery
and delivery subsystems and 20 years for process subsystems as noted above;
and salary and wage costs (fringe benefits, employment taxes, etc.) for all
employees. Also included are costs of replacement parts and other consum-
ables, utilities and other direct costs. This last category covers highly
specialized maintenance and service labor and materials that are required
too infrequently to support full-time specialized personnel, and therefore,
are purchased from special firms or factory representatives providing these
services.
56
-------
The cost of completing a landfill or developing a new landfill as part
of the landfill gas recovery/process/utilization system was not included as
a cost element. Revenues collected at the landfill gate or transfer station
to cover cost of landfill disposal similarly were not included. The cost
of the landfill was treated as a "sunk" cost for completed landfills, and
a non-accountable cost for new landfills since the general practice in the
United States is to set unit drop charges equal to unit landfill disposal
costs. Because landfill ing costs and corresponding drop charges vary wide-
ly among the different regions of the nation, this treatment avoids the
necessity of accounting for this highly variable cost-revenue element.
As a consequence of the assumptions made above and the inability to
accommodate certain cost items because of large regional variances, users
of these economic analyses should make appropriate adjustments to suit
local conditions and financial factors. The cost estimates and economic
analysis results are arranged so that major capital and operating costs and
interest and amortization are identified and can be readily adjusted when
evaluating the feasibility of a site specific project.
Alternative Recovery/Process/Uti1jzation System Cost Estimates
An assumption made for purposes of maintaining consistency between
cost estimates is that each system operates continuously with constant or
equivalent fluctuations in demand for the specified number of days per year.
Each capital cost estimate is divided into three subsystems:
1. Recovery subsystem
2. Process subsystem
3. Delivery subsystem
Costs of landfill gas recovery systems consisting of a number of wells,
a collection pipeline system and appropriate ancillaries were taken from
Figure 13, based on experience with a number of landfill gas projects. As
representative costs, the deep landfill, 30.5 to 45.7 m (100 to 150 ft)
curve was used. Shallow landfill gas mining costs are approximately twice
the cost of a deep landfill as shown on the curve because about twice the
number of wells are required for the same quantity of solid waste emplaced.
For purposes of standardization, the curves are based on a gas flow of 8.7
std cu m (600 scfm) per million metric tons (tons) of emplaced waste.
Figure 14 shows the relationships of normalized delivery subsystems
with product flow rates for the three types of products produced by the
alternative process systems: gas, steam and electricity. These curves
were developed from current A/E cost estimates assuming underground lines,
average soils and construction conditions. Cost of the delivery subsystem
is included in each alternative using average pipeline or transmission line
lengths: 5 km (3 mi) for gas and electric transmission lines, and 1.6 km
(1 mi) for steam lines.
A summary follows for each alternative, listing estimated capital and
57
-------
8S
GAS COLLECTION SYSTEM COSTS - $ x 106 (1977)
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69
GAS PIPELINE - $/m
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INSULATED STEAM PIPELINE/ELECTRICAL TRANSMISSION LINE - $/m
-------
annual operating costs for different LFG recovery rates and size of land-
fills.
Landfill Gas Processing Alternatives
Tables 8 through 11 list capital and annual operating cost data for
each of the four gas upgrade processes considered in this study: dehydra-
tion and compression; dehydration and carbon dioxide removal; dehydration,
carbon dioxide and nitrogen removal; and dehydration,carbon dioxide removal
and propane blending to provide landfill gas products with heating values
of 17727, 35454, 36387, and 37320 kJ/std cu m (475, 950, 975, and 1000 BTU/
scf), respectively. Figure 15 shows the variation of unit costs with daily
landfill gas recovery rates for these four processes compared against retail
and wholesale natural gas unit prices. The curves are as expected for the
four types of processing. As was expected, blending about 1 percent of
propane with landfill gas from which both water vapor and carbon dioxide
have been removed significantly reduces the cost of producing an upgraded
LFG with a heating value equivalent to that of natural gas.
The cost curves indicate that for local government ownership and opera-
tion of landfills, where there are no requirements for revenues to cover
taxes and return on investment, and when the gas can be sold for $2.00/37.32
MM kJ (MM BTUs) heating value; the systems described are economically viable
for landfills with low-flow rates. For dehydration only, a flow rate of
7.8 std cu m/min (0.4 MM scf/day, 275 scfm) may be viable. For dehydration
and carbon dioxide removal, 29.7 std cu m/min (1.5 MM scf/day, 1050 scfm)_
may be viable. For dehydration, carbon dioxide removal and propane blending,
48.8 std cu m/min (2.2 MM scf/day, 1525 scfm) may be viable. Finally, 94.8
std cu m/min (4.8 MM scf/day, 3350 scfm) may be viable for dehydration and
removal of both carbon dioxide and nitrogen. To relate gas flows to land-
fill size, a typical landfill with about 4.54 MM t (5 MM T) emplaced can be
expected to produce between 56.6 to 70.8 std cu m/min (2000 and 2500 scfm)
of LFG. Such a landfill typically would have a fill volume of about 9.94
MM cu m (13 MM cu yd) assuming 20 percent cover material. Thus, a large
landfill would be the only facility likely to produce enough gas to render
dehydration, carbon dioxide and nitrogen removal a break-even operation
even for local government.
The situation for private ownership and operation is much different
from that of local government and is discussed in the subsection on alter-
native economics.
Landfill Gas Conversion Alternatives
Tables 12 through 15 list capital and annual operating cost estimates
for alternative methods of converting LFG to other energy forms-steam or
electricity, and Table 16 list data for methanol synthesis from LFG. To
fully explore costs of electricity generation, three different prime movers
were used as described in the introduction of this section. Figure 16 de-
picts the relationships of unit costs for these conversion processes with
variations in landfill gas recovery rates.
60
-------
TABLE 8. COST ESTIMATE SUMMARY - ALTERNATE I
LFG Dehydration and Compression
Input (cu m/min)
Output (std cu m/min)
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem0
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)
No. Annual Days Operation
Annual Energy Output (10
kJ)
Cost ($/MM kJ)
13.74
13.03
80
300
47
30
80
457
99
636
12.2
48.3
15.1
75.6
70.0
8.0
21.0
10.0
109.0
184.6
331.9
350
116.2
1.589
34.69
32.85
159
428
55
40
100
623
175
957
,24.2
65.8
26.7
116.7
76.3
15.0
50.0
15.0
156.3
273.0
830. .1
350
290.6
0.939
69.38
65.70
309
590
70
55
115
""830"
249
1,388
47.1
87.7 »
38.0
172.8
80.0
25.0
92.0
17.5
214.5
387.3
1660.2
350
581.1
0.667
137.35
130.13
630
1,044
100
85
130
1^359"
330
2,319
96.0
143.6
50.3
289.9
86.0
45.0
180.0
28.8
339.8
629.7
3320.3
350
1162.1
0.542
a Dehydrated LFG at 17727 W/std cu rn (475 BTU/scf) and 155 kN/sq m (22.5 psig)
b 30.5 to 45.7 m (100 to 150 ft) average fill depth - Figure 13.
c 5 km (3 mi) long - Figure 14.
d Purchased services and maintenance.
61
-------
TABLE 9. COST ESTIMATE SUMMARY - ALTERNATE II
LFG Dehydration and Carbon Dioxide Removal
Input (cu m/min)
Output (std cu m/min )a
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem0
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)
No. Annual Days Operation
Annual Energy Output (109
kJ)
Cost ($/MM kJ)
47.29
13.74
215
1,130
70
90
135
1,425
100
1,740
32.8
150.6
15.2
198.2
96.0
20.0
20.0
25.0
161.0
359.2
700.9
330
231.4
1.552
94.45
27.47
430
1,740
95
140
210
2,185
157
2,772
65.5
230.9
23.9
320.4
99.0
35.0
38.0
45.0
217.0
537.4
1401.8
330
462.6
1.161
141.60
42.34
645
2,355
125
185
280
2,945
202
3,792
98.3
311.2
30.8
440.3
102.2
50.0
55.0
55.0
262.2
702.5
2153.3
330
710.6
0.989
a Upgraded LFG at 35454 kJ/std cu m (950 BTU/scf and 1379 kN/sq m (200 psig).
b 30.5 to 45.7 m (100 to 150 ft) average fill depth in Figure 13.
c 5 km (3 mi) long - Figure 14.
d Purchased services and maintenance.
62
-------
TABLE 10. COST ESTIMATE SUMMARY - ALTERNATE III
LFG Dehydration and Carbon Dioxide and Nitrogen Removal
Input (cu m/min)
Output (std cu m/min)
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem0
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)
No. Annual Days Operation
Annual Energy Output (10
kJ)
Cost ($/MM kJ)
47.29
11.89
215
1,830
120
135
220
2,305
92
2,612
32.8
243.6
14.0
290.4
150.0
35.0
40.0
40.0
265.0
555.4
616.6
330
203.5
2.729
94.45
24.64
430
2,770
165
190
335
3,460
148
4,038
65.5
365.7
22.6
453.8
153.0
60.0
75.0
65.0
353.0
806.8
1,284.5
330
423.9
1.903
141.60
40.36
645
3,675
235
255
445
4,610
195
5,450
98.3
487.2
29.7
615.2
156.2
85.0
115.0
80.0
436.2
1,051.4
2,106.7
330
695.2
1.512
a Upgraded LFG at 36387 kJ/std cu m (975 BTU/scf) and 1379 kN/sq m (200 psig),
b 30.5 to 45.7 m (100 to 150 ft) average fill depth - Figure 13.
c 5 km (3 mi) long - Figure 14.
d Purchased services and maintenance.
63
-------
TABLE 11. COST ESTIMATE SUMMARY - ALTERNATE IV
LFG Dehydration, Carbon Dioxide Removal and Propane Blending
Input (cu m/min)
Output3 (std cu m/min)
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem'"
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Other6
Total
Total Annual Op. Cost
Daily Energy Output CMM
kJ)
No. Annual Days Operation
Annual Energy Output (1CT
kJ)
Cost $/MM kJ)
47.29
14.22
215
1,170
80
94
140
1,484
103
1,802
32.8
156.8
15.7
205.3
96.0
110.0
22.0
30.0
258.0
463.3
762.1
330
251.5
1.843
94.45
28.43
430
1.785
no
145
217
2,257
160
2,847
65.5
238.5
24.4
328.4
99.0
210.0
41.0
52.0
402.0
730.4
1,524.3
330
503.1
1.452
141.60
43.70
645
2,405
145
190
288
3,028
204
3,877
98.3
320.0
31.1
449.4
102.2
321.0
59.0
60.0
542.2
991.6
2,342.0
330
772.9
1.283
a Upgraded LFG at 37320 M/std cu m (1,000 BTU/scf) and 1379 kN/sq m (200 psig)
b 30.5 to 45.7 m (100 to 150 ft) average depth - Figure 13.
d Incfudesmpropane atlo J06/L' ($0.40/gal), HHV = 93300 kJ/std'cu m.
e Purchased services and maintenance.
64
-------
O-l
en
3.0
2.5
2.0
1 1.5
00
o
o
1.0
0.5
N.G. RETAIK PRICE
.^6. WHOLESALE PRICE
JL
20
406080
LANDFILL GAS RECOVERY RATE - Std cu rn/min
Figure 15, Unit cost of alternative landfill gas products
-------
TABLE 12. COST ESTIMATE SUMMARY - ALTERNATE V
LFG Medium Pressure/Temperature Steam Generation
Input (cu m/min)
Output (kg/hr steam3)
Capital Costs (M$)
Recovery Subsystem**
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystemc
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)e
No. Annual Days Operation
g
Annual Energy Output (10
kJ)
Cost ($/MM kJ)
TO. 20
3,632
66
180
14
19
30
243
63
372
10.1
25.7
9.6
45.4
66.6
5.0
6.1
5.0
82.7
128.1
208.6
350
73.0
1.753
25.20
9,080
120
345
30
35
58
468
85
673
18.3
49.5
13.0
80.8
70.1
8.0
13.0
5.0
96.1
176.9
521.6
350
182.6
0.969
50.41
18,160
228
560
50
58
95
763
106
1,097
34.7
80.6
16.2
131.5
72.3
12.0
20.0
10.0
114.3
245.8
1,043.2
350
365.1
0.674
100.68
36,320
460
1,100
85
98
198
1,481
137
2,078
70.1
156.5
20.9
247.5
80.5
20.0
37.0
17.5
150.3
402.5
2,086.4
350
730.2
0.551
150.80
54,480
700
1,650
115
111
330
27206"
163
3,069
106.7
233.2
24.8
364.7
90.0
27.0
52.0
20.0
189.0
553.7
3,129.6
350
1,095.3
0.506
a 3448 kM/sq m, 260°C (500 psig, 500°F) steam, condensate returned, boiler
efficiency = 0.8.
b 30.5 to 45.7 m (100 to 150 ft) average depth - Figure 13.
c 1.6 km (1 mi) - Figure 14.
d Purchased service and maintenance.
e Heat delivered 2394 kJ/kg steam (1,031 BTU/lb steam).
66
-------
TABLE 13. COST ESTIMATE SUMMARY - ALTERNATE VI
LFG Electricity Generation (Steam Turbine)
Input (cu m/min)
Output (kJ/s)a
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystemc
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)
No. Annual Days Operation
Annual Energy Output (10 ^
kJ)
Cost ($/MM kJ)e
10.20
570
66
420
35
29
40
524
158
748
10.1
55.3
24. T
89.5
70.5
10.7
7.0
7.0
95.2
184.7
49.2
350
17.3
10.635
25.20
1,400
120
800
50
50
68
968
223
1,31.1
18.3
102.3
34.0
145.6
74.1
12.0
13.9
7.0
107.0
261.6
120.9
350
42.4
6 . 1 74
50.41
2,800
228
1,555
90
95
100
1,840
298
2,366
34.7
194.4
45.4
274.5
78.5
16.0
23.7
13.0
131.2
405.7
241.9
350
84.6
4.793
100.69
5,600
460
3,060
T25
180
200
3,565
395
4,420
70.1
376.7
60.2
507.0
90.7
27.6
41.5
20.0
179.8
686.8
483.8
350
169.3
4.057
150.8
8,500
700
4,500
195
260
360
5,315
455
6,470
106.7
561.7
69.3
737.7
106.2
32.5
63.2
30.0
231.9
969.6
734.3
350
257.0
2.824
a Delivered capacity (90% rated capacity) (1 kJ/s * 1 kW)
b 30.5 to 45.7 m (100 to 150 ft) average depth - Figure 13
c 5 km (3 mi) - Figure 14.
d Purchased service and maintenance.
e kWh = 3600 kJ.
67
-------
TABLE 14. COST ESTIMATE SUMMARY - ALTERNATE VII
LFG Electricity Generation (Gas Turbine)
Input (cu m/min)
Output (kJ/s)a
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem0
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)
No. Annual Days Operation
Annual Energy Output (10 9
kJ)
Cost ($/MM kJ)e
9.20
410
65
300
15
20
35
~~170
158
593
9.9
39.1
24.1
73.1
36.0
6.3
1.6
5.0
48.9
122.0
35.4
350
12.4
9.809
27.75
1,235
130
800
35
50
90
~~975
224
1,329
19.8
103.0
34.1
156.9
51.9
12.0
5.0
12.0
80.9
237.8
106.7
350
37.3
6.374
53.52
3,104
240
1,600
55
90
175
1,920
333
2,493
36.6
202.9
50.6
290.1
63.0
16.0
9.0
17.0
105.0
395.1
268.1
350
93.8
4.212
107.05
6,213
480
3,200
100
175
270
3,745
430
4,655
73.2
395.8
65.6
534.5
90.3
30.0
16.0
35.0
171.3
705.8
536.7
350
187.8
3.758
a Delivered capacity (86% rated capacity) (1 kJ/s = 1 kW).
b 30.5 to 45.7 m (100 to 150 ft) average 'depth.- Figure 13.
c 5 km (3 mi) - Figure 14.
d Purchased cervices and maintenance.
e kWh » 3600 kJ.
68
-------
TABLE 15. COST ESTIMATE SUMMARY - ALTERNATE VIII
LFG Electricity Generation (Gas Engine)
Input (cu m/min)
Output (kJ/s)a
Capital Costs (M$)
Recovery Subsystem^
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem0
Total System
Annual Operating^ Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/W Costs
Consumables & Parts
Utilities
Otherd
Total
Total Annual Op. Cost
Daily Energy Output CMM
kJ)
No. Annual Days Operation
Annual Energy Output (lu
kJ)
Cost ($/MM U)e
8.86
650
62
285
65
30
60
440
166
668
9.4
46.5
25.3
81.2
36.0
7.5
2.0
10.6
56.1
137.3
56.2
330
13.6
7.400
17.7
1,300
88
530
no
60
120
820
217
1,125
13.4
86.6
33.1
133.1
65.7
15.0
3.0
17.5
101.2
234.3
112.3
330
37.1
6.315
53.1
3,900
240
1,580
270
150
320
2,320
344
2,904
36.6
245.2
52.4
334.2
170.0
46.5
8.5
45.0
270.0
604.2
336.9
330
111.2
5.434
106.2
7,800
490
3,000
480
270
600
4,350
441
5,281
74.7
459.7
67.2
601.6
305.8
90.0
16.5
85.0
497.3
1,098.9
673.8
330
222.4
4.941
159.3
11,700
750
4,400
690
370
860
6,320
496
7,566
114.3
667.9
75.6
857.8
432.6
135.0
24.0
130.0
721.6
1,579.4
1,010.7
330
333.5
4.736
a Delivered capacity - 100% rated capacity.
b 30.5 to 45.7 m (100 to 150 ft) average depth - Figure 13.
c 5 km (3 mi) - Figure 14.
d Purchased service and maintenance.
e kWh * 3600 kJ.
69
-------
TABLE 16. COST ESTIMATE SUMMARY - ALTERNATE IX
LFG Methanol Synthesis
Input (cu m/min)
Output (cu m/day)
Capital Costs (M$)
Recovery Subsystem*
Process Subsystem
Equipment
Facilities
Design
Construction
Total
Delivery Subsystem"
Total System
Annual Operating Costs (M$)
Amortization & Interest
Recovery Subsystem
Process Subsystem
Delivery Subsystem
Total A&I
Salaries & Wages &
S/-W Costs
Consumables & Parts
Utilities
Other
Total
Total Annual Op. Cost
Daily Energy Output (MM
kJ)c
No. Annual Days Operation
Annual Energy Output 00
kJ)
Cost($/MM kJ)
Cost ($/L)
98.27
45.42
452
4,200
300
450
750
5,700
-
6,152
68.9
602.3
-
67172
171.3
35.0
10.0
35.0
251.3
922.5
795.6
300
238.7
3.864
0.068
157.32
79.49
741
6,120
400
580
1,100
8,200
-
8,941
112.9
866.5
-
97974
260.5
53.0
15.0
53.0
381.5
1,360.9
1,392.3
300
417.7
3.258
0.057
a 30.5 to 45.7 m (100 to 150 ft) average depth - Figure 13.
b No delivery system required; truck or tank car loading station included
in the system.
c 17.52 MM kJ/cu m (62,903 BTUs/gal) methanol.
70
-------
12.50
10.00
7.50
OO
o
O
5.00
ELECTRICITY - STEAM TURBINE
ELECTRICITY - GAS TURBINE
ELECTRICITY - GAS
2.50
STEAM
_L
J_
_L
JL
20 40 60 80 100 120
LANDFILL GAS RECOVERY RATE - Std cu m/min
Figure 16. Unit cost of alternative LFG conversion processes.
-------
As can be expected from series or cascaded conversion of process ef-
ficiencies, generation of steam is by far the lowest cost process of the
three alternative primemovers used for driving a comparable generator. The
difference between use of a boiler-steam turbine combination and gas turbine
is not significant, while use of gas engine-generator sets is indicated to
be somewhat higher in cost beyond a gas recovery rate of about 39.5 std cu
m/min (2 MM scf/day), but is somewhat less costly than the two turbines
when rates are less than about 29.7 std cu m/min (1.5 MM scf/day). This
results because small gas engines have about the same thermal and mechanical
efficiency as large units, whereas turbine thermal efficiencies tend to
decrease as horsepower is reduced beyond certain levels.
Methanol synthesis is shown on Figure 16 for convenience. For large
landfills the cost to produce methanol on an equivalent BTU basis are nearly
six times more expensive than dehydrated landfill gas and about twice the
cost of LFG with water vapor, carbon dioxide and nitrogen removed.
Using steam priced at $2.55/1.05 MM kJ (MM BTUs) (based on firing
natural gas costing $2/1.05 MM kJ (MM BTUs)), steam generation would_be a
break-even operation for a local government owned and operated facility at
a LFG flow rate of about 3.9 std cu m/min (0.2 MM scf/day). For electric-
ity generated and sold at a retail price of $0.05/kw-hr, break-even LFG
flows are again about 3.9 std cu m/min (0.2 MM scf/day). For electricity
sold at a wholesale rate of $0.03 to local electric utilities, the break-
even LFG flow for local government operated facility is about 15.7 std cu
m/min (0.8 MM scf/day) for both types of turbine prime-movers and about
5.9 std cu m/min (0.3 MM scf/day) for a gas engine generator set. The cost
situation as it relates to process facilities operated by private enterprise
is discussed in the next subsection.
Alternative Recovery/Process/Utilization System Economics
Comparative economics were developed for each landfill gas recovery/
process/utilization alternative using the cost data provided in Tables 8
through 16, divided into the same two groups: LFG upgrade processes/products
and conversion processes/products. Costs and revenues were calculated on an
annualized basis assuming 330 days per year for more complex upgrading pro-
cesses and 300 days for methanol synthesis.
Economic indicators to be used are:
o Gross Surplus or Deficit (Profit or Loss)
o Capital Investment
o Investment Payback Period
o Capital Cost per Unit Daily Capacity (Output)
These indicators permit direct comparison among all alternatives re-
gardless of product, although LFG upgrade products that are fuels should
72
-------
not be compared with conversion products like steam and electricity that
are a product of a series of efficiency factors which influence economic
results. For example, dehydration of LFG has a process efficiency factor
of about 95 percent, steam about 80 percent, electricity generation about
30 to 35 percent, and methanol synthesis about 32 percent. However, to ex-
tract the energy from upgraded LFG and methanol, the combustion process
imposes another efficiency factor (thermal in this case) that can range
from about 20 to 80 percent depending upon method. Consequently, the fuels
are compared as a group and steam and electricity are compared as a second
group.
All economic indicators are in gross terms; that is, gross surplus or
deficit, gross return on investment, gross investment payback period based
on revenues less direct operating costs. Because there is no useful way to
approximate indirect costs (general and administrative, corporate or parent
company overhead, etc.) which can vary from zero to as much as fifty percent
of direct costs depending upon the landfill operating entity's relationship
to other business organizations (independent operation, subsidiary, division,
etc.), no attempt has been made to include indirect expenses. However, it
is possible to approximate a normalized annual return on investment after
profit and taxes for private enterprise in order that generalized division
between acceptable and unacceptable return on investment (ROI) can be es-
tablished. The expression or minimum acceptable ROI used for this purpose
is:*
(ROI) = P x I = GP = NP + LT + F/SIT
where: P = percent of investment returned annually
I = total system investment
NP = net profit at 10 percent of investment
LT = local business property taxes at 50 percent of gross profits
F/SIT = federal and state income taxes at 50 percent of gross profits
GP = gross profit or surplus
Thus, for private enterprise which is to earn an annual net profit of ten
percent on its investment, pay both local business property taxes and
federal and state income taxes; the expression works out to:
GP = P x I = 0.1 I + 0.05 I + 0.5 P x I
solving for P, p = p.15 = 0.3 or 30%
0.5
For local government ownership and operation of a landfill recovery/
processing/utilization system, neither profits or taxes are involved. How-
* Similar technique used in Reference 1.
73
-------
ever, recognizing the risk involved and the uncertainty of the period during
which the landfill is likely to produce LFG at a rate sufficient to warrant
recovery and processing, it is prudent for local government to establish a
reserve for contingency amounting to the equivalent of ten percent of total
investment per year. Thus, for government entities:
P x I = 0.1 I and P = 0.1 or 10%
Calculating the investment payback period for these alternatives on a
simple non-compounded basis, the expression is:
PP = I
(R^OC + A&I - I)
where: PP = payback period in years
I = capital investment
R = annual revenues
OC = annual operating costs
A&I = annual amortization and interest charges included in OC
I = annual interest charge on total investment
This expression simply substitutes annual interest on the total invest-
ment for the constant annual amortization and interest on the decreasing
loan balance. Annual operating costs are calculated in order to indicate
the amount of surplus funds (revenues less operating costs) that would be
available annually to accumulate in a reserve fund until that fund equals
total investment.
Landfill Gas Processing Alternatives-
Tables 17 through 20 present summaries of the economics of the four
LFG upgrade processes for various LFG recovery rates. The significant in-
dicators are the operating cost per unit of product (million BTUs heating
value) which must be sufficiently below the unit price that a reasonable
return on investment can be achieved for private enterprise and at least
equal to the unit price for government operated facilities. Figure 17 shows
the variation of gross return on investment and unit capital cost (dollars
per million BTUs of product produced daily) for the four LFG upgrade pro-
cesses/products.
For private enterprise operations, it is shown that only the LFG de-
hydration alternative will provide a 30 percent return on investment at a
daily gas recovery rate of about 33.4 std cu m/min (1.7 MM scf/day). How-
ever, under some circumstances, local gas utilities have indicated a will-
ingness to pay a reasonable return above the cost of producing usable gas.
In the near future, natural gas imported from Canada and liquid natural gas
imported from Indonesia will be priced at a wholesale rate of about $3.507
74
-------
TABLE 17. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE I
LFG Dehydration and Compression9
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output(109 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/MM kJ)b
Daily (M$)
Annual (M$)
Gross Surplus (Deficit)
Capital Investment (M$)
Gross Return on Invest-
ment (%}
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
331.9
350
116.2
184.6
1.589
1.90
0.63
220.4
35.8
636
5.6
11.1
1.917
830.1
350
290.6
273.0
0.939
1.90
1.58
551.3
278.3
957
29.1
3.1
1.157
1660.2
350
581.1
387.3
0.667
1.90
3.15
1102.6
715.3
1388
51.5
1.8
0.835
3320.3
350
1162.1
629.7
0.542
1.90
6.30
2205.1
1575.4
2319
67.9
1.4
0.702
a Dehydrated LFG at 17727 kJ/std cu m and 155 kN/sq m (475 BTU/scf, 22.5
psig).
b Retail rate - gas delivered to user.
75
-------
TABLE 18. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE II
LFG Dehydration and Carbon Dioxide Removal9
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output (10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/MM kJ)b
Daily (M$)
Annual (M$)
Gross Surplus (Deficit)
Capital Investment (M$)
Gross Return on Invest-
ment (%)
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
700.9
330
231.4
359.2
1.552
1.57
1.10
362.1
2.9
1740
0.2
32.7
2.486
1401.8
330
462.6
537.4
1.161
1.57
2.19
724.2
186.8
2772
6.7
10.2
1.973
2153.3
330
710.6
702.5
0.989
1.57
3.37
1112.4
409.9
3792
1.08
7.2
1.765
a Upgraded LFG at 35454 kJ/std cu m and 1379 kN/sq m (950 BTU/scf, 200
psig).
b Wholesale rate - gas delivered to local gas utility.
76
-------
TABLE 19. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE III
LFG Dehydration and Carbon Dioxide and Nitrogen Removal9
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output(10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/MM kJ)b
Daily (M$)
Annual (M$)
Gross Surplus (Deficit)
Capital Investment (M$)
Gross Return on Invest-
ment (%)
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
616.6
330
203.5
555.4
2.729
1.57
0.97
318.5
(236.9)
2612
-
-
4.231
1284.5
330
423.9
806.8
1.903
1.57
2.01
663.6
(143.2)
4038
-
-
3.140
2106.7
330
695.2
1051.4
1.512
1.57
3.30
1088.3
36.9
5450
0.7
28.8
2.590
a Upgraded LFG at 36387 kJ/std cu m and 1379 kN/sq m (975 BTU/scf, 200
psig).
b Wholesale rate - gas delivered to local gas utility.
77
-------
TABLE 20. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE IV
LFG Dehydration, Carbon Dioxide Removal and Propane Blending
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output (10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/MM kJ)b
Daily (M$)
Annual (M$)
Gross Surplus (Deficit)
Capital Investment (M$)
Gross Return on Invest-
ment (%)
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
762.1
330
251.5
463.3
1.843
1.57
1.19
393.7
(69.6)
1802
-
-
2.362
1524.3
330
503.1
730.4
1.452
1.57
2.39
787.5
57.1
2847
2.0
19.9
1.869
2342.0
330
772.9
991.6
1.283
1.57
3.67
1209.9
218.3
3877
5.6
11.5
1.660
a Upgraded LFG at 37320 kJ/std cu m and 1379 kN/sq m (1000 BTU/scf, 200
psig).
b Wholesale rate - gas delivered to local gas utility.
78
-------
6Z
CAPITAL COST/MM BTUs DAILY CAPACITY (M$)
-s
(0
o
o
3
o
o
o
o
Ol
-s
t/J
o
3
OJ
fD
-s
3
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c-t
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a.
-h
to
&>
TO
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Q-
c
o
GROSS RETURN ON INVESTMENT - PERCENT
-------
1.05 MM kJ (MM BTUs) which could render one or more of these three LFG up-
grade processes economically viable at reasonable gas recovery rates.
For LFG recovery/processing/utilization systems operated by local
governments which pay no taxes and require only establishment of a contin-
gency fund (set at ten percent ROI), only dehydration meets this criteria
at about 17.7 std cu m/min (0.9 MM scf/day). The other three processes are
of questionable practicality if the contingency fund requirement is to be
met since required daily flows are well beyond 157.2 std cu m/min (8 MM
scf/day). On a break-even basis only and without a contingency fund re-
quirement dehydration with carbon dioxide removal, dehydration and carbon
dioxide removal with propane blending, and dehydration with both carbon di-
oxide and nitrogen removal require about 47.2, 78.6 and 141.5 std cu m/min
(2.4, 4, and 7.2 MM scf/day) recovery rates, respectively.
Landfill Gas Conversion Alternatives--
Tables 21 through 25 list economic indicators for steam generation,
electricity generation using raw landfill gas as the fuel, and for conver-
sion of LFG of methanol. Figures 18 and 19 show curves of the variation of
gross return and investment and unit capital costs against variations in
daily LFG recovery rates. For private enterprise which requires a ROI of
30 percent, steam generation and gas turbine generation of electricity with
the power sold at retail rates requires daily LFG flows of about 19.65 std
cu m/min (1 MM scf). Power generated by a steam turbine which sells at
retail rates requires an LFG flow of about 35.4 std cu m/min (1.8 MM scf/
day). Electricity generation using a gas engine with power sold at retail
rates and gas turbine electricity generation with power sold at wholesale
require LFG flows of about 48.2 std cu m/min (2.3 MM scf/day). Electricity
generated by steam turbine or gas engine sold at wholesale rates cannot
meet the 30 percent ROI requirement at reasonable daily LFG flows.
If local government operates the systems, flow rates necessary to meet
the 10 percent ROI requirement for a prudent contingency fund are about
3.9 std cu m/min (0.2 MM scf/day) for gas engine electricity generation
sold at retail, 9.8 std cu m/min (0.5 MM scf/day) for both steam generation
and gas turbine generated electricity sold at retail, 11.8 std cu m/min
(0.6 MM scf/day) for steam turbine generated electricity sold at retail, and
about 15.7 std cu m/min (0.8 MM scf/day) for gas turbine electricity sold
at wholesale rate. Electricity generated by a steam turbine requires an LFG
recovery rate of about 31.4 std cu m/min (1.6 MM scf/day) and power gener-
ated by a gas engine requires about 39.3 std cu m/min (2 MM scf/day) when
sold at wholesale. Conversion of LFG to methanol does not provide the ROI
required by private enterprise at any reasonable LFG recovery rate; for
local government with its 10 percent ROI, it requires about 167 std cu m/min
(8.5 MM scf/day), or in a break-even situation it requires about 68.8 std cu
m/min (3.5 MM scf/day.
In comparing unit capital costs of the various alternatives, one must
keep in mind the system losses which occur in the use of the final energy
product. Though steam production has the lowest unit capital costs, it is
also one of the least efficient forms of energy utilization. Methanol syn-
80
-------
TABLE 21. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE V
LFG Medium Pressure/Temperature Steam Generation9
Daily Energy Output (MM kJ) 208.6 521.6 1043.2 2086.4 3129.6
No. Annual Days Operations 350 350 350 350 350
Annual Energy Output(109 kJ) 73.0 182.6 365.1 730.2 1095.3
Annual Operating Cost (M$) 128.1 176.9 245.8 402.5 553.7
Cost ($/MM kJ) 1.753 0.969 0.674 0.551 0.506
Cost ($/M kg steam) 3.954 2.183 1.519 1.244 1.140
Revenues
Rate ($/M kg Steam)b 5.64 5.64 5.64 5.64 5.64
Daily (M$) 0.49 1.22 2.44 4.86 7.28
Annual (M$) 172.4 426.1 852.3 1702.1 2549.6
Gross Surplus (Deficit) 45.3 249.2 606.5 1299.6 1995.9
Capital Investment (M$)
Gross Return on Invest-
ment (%)
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
372
12.2
6.4
1.78
673
37.0
2.5
1.29
1079
55.3
1.7
1.05
2078
62.5
1.5
1.00
3069
65.0
1.5
\
0.98
a 3448 kN/sq m, 260°C steam (500 psig, 500°F), condensate returned from user.
b Steam value based on BTUs of LFG used at retail rate of $1.90/MM kJ
($2/MM BTUs) and 2396 kJ/kg (1031 BTU/lb) of steam.
81
-------
TABLE 22. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE VI
LFG Electricity Generation (Steam Turbine)
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output (10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues9
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Capital Investment (M$)
Gross Return on Investment (%)
Investment Payback Period
(Years)3
System Capital Cost/MM kJ
Daily Capacity (M$)
Cost/MW Capacity
49.2
350
17.3
184.7
10.685
0.05
0.68
239.3
54.6
0.03
0.410
143.6
(41.1)
748
a 7.3
9.3
15.199
1312.2
120.9
350
42.4
261.6
6.174
0.05
1.68
587.8
326.2
0.03
1.007
352.7
91.1
1311
24.9/
6.9
395£
10.844
936.4
241.9
350
84.6
405.7
4.793
0.05
3.36
1176.1
770.4
0.03
2.016
705.6
299.9
2366
3f264
268/3
9.782
845.0
483.8
350
169.3
686.8
4.057
0.05
6.72
2352.1
1665.3
0.03
4.032
1411.3
724.5
4420
V/4
2&
9.137
789.3
734.3
350
257.0
969.6
2.824
0.05
10.20
3570.2
2600.6
0.03
6.120
2142.1
1172.5
6470
T 6 n
1 O 1
4.8
8.814
761.2
a $0.5/.03 per kWh (1 kWH = 3600 kJ) - retail to user/wholesale to electric
utility.
82
-------
TABLE 23. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE VII
LFG Electricity Generation (Gas Turbine)
Daily Energy Output (MM kJ)
No. Annual Days Operations
Q
Annual Energy Output (10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Capital Investment (M$)
Gross Return on Investment (%)a
Investment Payback Period
(Years)3
System Capital Cost/MM kJ
Daily Capacity (M$)
Cost/MW Capacity
35.4
350
12.4
122.0
9.089
0.05
0.49
172.2
50.2
0.03
0.295
103.3
(18.7)
593
8.5
8.1
16.746
1446.3
106.7
350
37.3
237.8
6.374
0.05
1.48
518.6
280.8
0.03
0.889
311.2
73.4
1329
39. 0/
23.4
4.1/
11.3
12.457
1076
268.1
350
93.8
395.1
4.212
0.05
3.73
1303.7
908.6
0.03
2.234
782.2
387.1
2493
52.3/
31.4
2.57
5.4
9.298
803.2
536.7
350
187.8
705.8
3.758
0.05
7.46
2609.4
1903.6
0.03
4.473
1565.6
859.8
4655
56.17
33.6
2.3/
4.7
8.634
749.2
a $0.57.03 per kWh (1 kWH = 3600 kJ) - retail to user/wholesale to electric
utility.
83
-------
TABLE 24. .ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE VIII
_FG Electricity Generation (Gas Engine)
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output (10 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Revenues
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Rate ($/kWh)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit) (M$)
Capital Investment (M$)
Gross Return on Investment (%)
Investment Payback Period
(Years)3
System Capital Cost/MM kJ
Daily Capacity (M$)
Cost/MW Capacity
56.2
330
18.6
173.3
7.400
0.05
0.78
257.5
120.2
0.03
0.468
154.5
17.2
668
18.0/
2.6
4.6/
16.0
11.891
1027.7
112.3
330
37.1
234.3
6.315
0.05
1.56
514.6
280.3
0.03
0.936
308.7
74.4
1125
24.97
2.6
3.5/
10.1
10.022
865.4
336.9
330
111.2
604.2
5.434
0.05
4.68
1544.2
940.0
0.03
2.808
926.5
322.3
2904
28. 9/
11.1
2.8/
7.1
8.620
744.6
673.8
330
222.4
1098.9
4.941
0.05
9.36
3088.9
1990.0
0.03
5.616
1853.3
754.4
5281
37. 7/
14.3
2.5/
5.8
7.838
676.9
1010.7
330
333.5
1579.4
4.736
0.05
14.04
4633.0
3053.6
0.03
8.424
2779.8
1200.4
7566
40.4/
15.9
2.37
5.3
7.486
767.7
a $0.57.03 per kWh (1 kWH = 3600 kJ) - retail to user/wholesale to electric
utility.
84
-------
TABLE 25. ECONOMIC ANALYSIS SUMMARY - ALTERNATIVE IX
LFG Methanol Synthesis
Daily Energy Output (MM kJ)
No. Annual Days Operations
Annual Energy Output(l09 kJ)
Annual Operating Cost (M$)
Cost ($/MM kJ)
Cost ($/L)
Revenues
Rate ($/L)
Daily (M$)
Annual (M$)
Gross Surplus (Deficit)
Capital Investment (M$)
Gross Return on Invest-
ment (%)
Investment Payback Period
(Years)
System Capital Cost/MM kJ
Daily Capacity (M$)
Cost ($/cu m)
365.9
300
109.8
563.7
5.146
0.090
0.092
1.93
675.5
74.0
3755
2.0
23.1
10.261
179.74
795.6
300
238.7
922.5
3.864
0.068
0.092
4,20
1470.0
337.5
6125
5.5
12.5
7.699
134.85
1392.3
300
417.7
1360.9
3.258
0.057
0.092
7.35
2572.5
844.1
8941
9.4
8.4
6.421
112.50
85
-------
15
00
CTl
CJ
cC
Q-
=c
o
oo
o
-3
o
10
RETAIL ELECTRICITY - $0.05/kWh
cc:
LU
D_
OO
o
o
eC
ii
D_
20
40
60 80 100 120
LANDFILL GAS RECOVERY RATE - Std. cu m/min
Figure 18. Economic comparison of alternative LFG conversion processes.
-------
Z8
GROSS RETURN ON INVESTMENT - PERCENT
m
o
o
^
o
I.
o
o
o
-a
DJ
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o
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CD
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~i
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rr>
-------
thesis, which has a much higher unit capital cost, produces a liquid fuel
which can be converted to usable energy with considerably greater efficiency.
SUMMARY
Comparisons of alternative uses for landfill gas and the processes re-
quired to produce the alternative products suggest that:
1. Use of dehydrated landfill gas as a supplementary or replacement
fuel shows the greatest promise from the standpoints of technical
and economic feasibility, applicability to the broadest variety of
landfill sites in terms of their volumes and gas flow rates, and
suitability for development and operation by either private enter-
prise or local government entities.
2. Further upgrading of LFG (removal of carbon dioxide or both carbon
dioxide and nitrogen) is presently too expensive to be feasible
for private enterprise and is feasible for local governments only
on a break-even economic basis for landfills of reasonable size and
when sold to local utilities at wholesale prices. (Except for un-
usual circumstances that enhance the financial picture.)
3, Generation of steam or electricity using raw LFG as the fuel is
technically and economically feasible at reasonable LFG recovery
rates for both private enterprise and local government when sold
to users at retail prices.
4. Any of the three prime methods used to generate electricity using
raw LFG as fuel can be economically feasible for local government
while only electricity generated by gas turbines is economically
feasible for private enterprise when sold to local utilities at a
wholesale price.
88
-------
SECTION 6
LANDFILL DESIGN AND OPERATIONAL TECHNIQUES FOR
ENHANCEMENT OF GAS GENERATION AND RECOVERY
This section reviews current state of the art landfill site selection
criteria, design principles and operational techniques that show promise of
enhancing landfill gas generation and recovery. Desirable characteristics,
principles and techniques are briefly discussed and evaluated as to pro-
bable applications, practicality, typical likely incremental costs and
probable results, both favorable and unfavorable.
Most of the information presented in this section pertains to the sit-
ing, design and operation of new landfills planned for LFG recovery and
utilization. However, some of the operating techniques should be appli-
cable to completed or currently operational landfills which are candidates
for LFG recovery systems.
Production of leachates in landfills and percolation of these high BOD
and COD liquids into the ground water table must be prevented. Thus, site
selection, design and operational techniques must be compatible with proper
leachate control. Desirable landfill conditions are those which prevent
leachate from reaching ground water tables, minimize the production of lea-
chate through proper surface drainage and the use of impervious cover mate-
rials, and prevent landfill gas migration in any direction. However, there
are few sites that present ideal topographical, geological and soil condi-
tions so design measures and operational techniques often must be used to
minimize the pollution potential of landfills.
Certain measures for enhancement of gas generation may be in opposition
to control of leachate production and percolation. For example, available
data suggests that for optimal gas generation, the emplaced waste should
have at least a 50 percent moisture content. Because landfill gas is typi-
cally at or near saturation, this moisture content must be maintained by
the introduction/of water from the surface or outside the landfill. This
dictates the usd of permeable cover material that permits percolation of
surface water, but at the same time prevents the desirable ventilation
of landfill gas or inhalation of air during recovery. A relatively wet solid
waste mass emplaced in a landfill tends to accelerate leachate formation and
drainage to the bottom of the landfill which, in turn, tends to increase the
hydraulic pressure that can increase percolation through the bottom of the
landfill into the ground water table. Thus, there can be a basic conflict
between minimization of leachate formation and maintenance of optimal con-
ditions for landfill gas formation.
89
-------
Various types of landfill designs that respond to variations in pre-
vailing geology, soils and terrain are not covered because this subject is
adequately delineated in a number of EPA documents. Also there^gre
several recent reports on the subjects of gas and leachate control.
Accordingly, the emphasis of this section is on a discussion of the suita-
ability and applicability of special measures that are believed to have po-
tential for enhancing gas generation and collection in order to improve the
likelihood of economic viability for landfill gas recovery/processing/
utilization projects.
Material presented herein is organized into three divisions:
1. Landfill site selection and characteristics
2. Landfill design
3. Landfill operational techniques
LANDFILL SITE SELECTION AND CHARACTERISTICS
The major criteria governing the selection of a new landfill site that
is to incorporate LFG recovery/processing/utilization are essentially the
same as for any landfill. Additional criteria are imposed, however, in or-
der to minimize the costs of the recovery system and enhance both gas genera-
tion and gas characteristics to the extent practical.
Size and Geometry
To take advantage of economies-of-scale characteristics of continuous
process systems, the site should be as large as possible. Figure 20 shows
curves of LFG recovery rates as functions of in-place solid waste quantities
and daily LFG production. For example, based on typical landfill parameters
(compacted waste density 592 kg/cu m (1000 Ib/cu yd), 20 percent cover
material by volume), fill areas per million tons of emplaced solid waste
are:
Amount of waste Fill area MM Perimeter
in-place Average depth tons S.W. area
0.9 MM t (1 MM T) 15.2 m (50 ft) 12.5 ha (31 ac) 17.4 ha (43 ac)
0.9 MM t (1 MM T) 30.5 m (100 ft) 6.5 ha (16 ac) 12.5 ha (31 ac)
0.9 MM t (1 MM T) 45.7 m (150 ft) 4.5 ha (11 ac) 10.1 ha (25 ac)
The perimeter area is an additional area for screening, noise attenua-
tion and separation of the fill area from adjacent land uses. At a mini-
mum, it should be about 122 m (400 ft) in width. As the fill area increases,
the ratio of perimeter area to the fill area decreases.
Figure 16 in Section 4 showed that unit capital and operating costs of
LFG recovery and basic dehydration became nearly constant above 544t
(600 T) per day equivalent daily capacity. This equals about 77825 std cu
90
-------
6 _
O
=C
00
O
00
O
GO
O
LANDFILL GAS RATE - MM scf/day
Figure 20. Landfill gas generation rates for various solid waste quantities in-pi ace,
-------
m
, (2 75 MM scf) of LFG per day (1 MM scf/day is equivalent to a capacity of
217 4 T/day). However, the rate of increase in unit capital and operating
costs as capacity decreases is gradual so that desirable landfill size for
LFG recovery/processing/utilization falls in the range of 35.4 to 54 std cu
m/min (1.8 to 2.75 MM scf/day). This equates to a fill area ranging from
2 27 to 3.44 MM t (2.5 to 3.8 MM T) of solid waste in place (using a nominal
LFG generation rate of Figure 20 of 15.6 cu m/min/MM t (500 cfm/MM T which
relates to the generally accepted 0.13 scf LFG/lb of solid waste/yr)._ These
LFG recovery rates and quantities of solid waste in place are_the basis for
the fill and perimeter areas for minimal desirable landfill sizes listed in
Table 26. Also listed are the estimated unit costs taken from Figure 15 in
Section 5.
Smaller landfills also can be mined for LFG but the unit cost of dehy-
drated LFG begins to rise more rapidly. For example, a fill area half the
size of the low end of the desirable range, 17.7 std cu m/min (0.9 MM scf/
day recovery rate) is estimated to have a unit cost of $1.48 per 37.32 MM kJ
(MM BTUs).
Also figuring strongly into the unit capital and operating costs_of LFG
recovery/processing/utilization systems is the average depth of the fill
area. Costs increase as the average fill depth decreases primarily because
of the more extensive and thus more costly recovery system as depicted in
Figure 13 of Section 5. It is highly desirable that the site selected for
a new landfill be designed and developed for as deep a fill area as possible
for LFG recovery/processing/utilization.
The surface configuration of landfills varies widely. However, it is
desirable for LFG recovery systems that the fill area be approximately
square or rectangular and the side dimensions be multiples of about 69 to,J6^
ra (225 to 250 ft) for optimal coverage of recovery well influence areas.
The geometry of fill areas is more critical for small landfills than for
large ones.
Other Desirable Characteristics
The presence of a highly impermeable geological structure underlying
the fill area is particularly important for those landfills planning LFG
recovery systems. It is highly desirable to maintain a relatively high
moisture content in the emplaced solid waste in order to enhance gas genera-
tion, either by the regular addition of water to the fill area, leachate
recycling or possibly both. The impermeable underlying structure should
slope to one or more low points so that leachate can drain, be collected in
sumps and be removed or recycled. While it is often possible to shape the
bottom of the fill area as desired, should the underlying structure be rock
or semi-rock, the cost might be high for re-sloping it to the desired con-
tours.
The sides of the fill area similarly should be composed of highly im-
permeable materials to contain leachates and landfill gas.
92
-------
TABLE 26. MINIMUM AREAS DESIRABLE FOR LANDFILL GAS RECOVERY PROJECTS
vo
CO
Average
fill depth
(m)
15.2
15.2
30.5
30.5
45.7
45.7
Solid waste
quantity
(MM t)
2.27
3.45
2.27
3.45
2.27
3.45
Daily LFG
recovery rate
(std cu m/day)
50976
77880
50976
77880
50976
77880
Fill area
(ha)
31.36
47.67
16.19
24.61
11.13
16.92
Minimum
perimeter
area
(ha)
27.32
33 .67
19.63
24.20
16.27
20.07
Total
landfill
area
(ha)
58.68
81.34
35.82
48.81
27.40
36.99
Estimated
product
cost
. ($/MM kJ)
0.93
0.74
0.93
0.74
0.93
0.74
Based on mid-range gas generation of 22481 cu m/day/MM t (0.72 MM scf/day/MM T) in-place.
Estimated unit costs for LFG recovery and dehydration from Figure 15, Section 4.
-------
The topography of the site should be such that natural surface drainage
can be readily controlled and the fill surface contoured to provide con-
trolled drainage of precipitation to provide the desired level of percola-
tion into the fill for moisture control.
While the availability of suitable cover material is a criterion for
the selection of any landfill site, this is a particularly important factor
for a site that is to incorporate a LFG recovery system. The cover mate-
rial must be highly impermeable if the additional cost of importing material
from another site or adding chemicals to the soil to decrease its permeabil-
ity are to be avoided.
Pertaining to the selection of a landfill site that is to include LFG
recovery and processing: There should be one or more multiple large fuel
users in the immediate vicinity of the site (e.g., industry, institutions,
power plants, etc.) preferably within a radius of 8 km (5 mi)?or there
should be a natural gas transmission main or electricity transmission line
within a few kilometers (miles) of the site. It would be useless to select
and develop a landfill site for LFG recovery/processing/utilization if
there were no large fuel/energy product users in the immediate vicinity
that were interested in purchasing and using the product when it became
available. Accordingly, it is well to survey potential users and alterna-
tive sites as part of the survey. This survey is necessary not only for
basic site selection, but to determine which of the alternate LFG fuel/
energy products can be sold and thus which of the alternative process sys-
tems should be implemented.
LANDFILL DESIGN
There are a number of alternative approaches to the planning and design
of a landfill that is to incorporate LFG recovery and processing which ap-
ply under different site conditions. In general these approaches are not
greatly different from those applied to a landfill which is not expected to
incorporate an LFG system, although certain aspects become more important
in order to optimize LFG generation and make recovery as efficient and com-
plete as possible.
For the site on which a LFG system is to be added, solid waste cells
should be located in a manner that will facilitate an efficient recovery
well and collection pipeline complex. All fill areas should be contiguous
and the final fill area contour should be sloped for drainage purposes.
This applies to both trench or area method landfills. Use of stepped con-
tours in final grading of fill areas on steep slopes can be used as neces-
sary and fill area plateaus at different elevations also can be accommo-
dated as appropriate to the original terrain contours. However, use of
these design features will increase the cost of the recovery system, espe-
cially the collection pipelines, manifolds and pressure balancing valves.
A major design difference between a landfill with LFG recovery and a
standard fill is in the area of leachate collection and control. While
leachate can be controlled in a standard landfill by minimizing the entrance
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of water into the fill, it is desirable for water to percolate into the
fill to enhance gas generation. This will increase leachate generation well
beyond the amount otherwise formed, and a system of bottom drainage channels,
collection sumps and recovery wells will be required in the basic landfill
design and development plan. This system will be similar to that included
in a landfill that is to receive hazardous liquids and sludges as well as
solid waste, but usually not required for a fill limited to municipal solid
waste unless the underlying geology and/or water table height are unfavor-
able.
Various alternative approaches to design of landfills with LFG systems
are outlined and discussed below. Each alternative is evaluated and ap-
proximate costs stated followed by a cost-effectiveness example, where in-
formation is available.
Site Lining
Gas and leachate migration from a landfill can be controlled by the
use of appropriate barriers within the confines of the site. The objective
of placing suitable barriers under and along the sides of the fill area is
to prevent, or at least, minimize the outward movement of gas and leachate
beyond site boundaries. Use of impermeable barriers also tends to increase
the potential for recovery of landfill gas. Low permeability materials used
can be natural, such as certain types of soil; or synthetic, such as plas-
tic or rubber membranes. The placement of low permeability soil under and
along the sides of the site can be accomplished with small additional ef-
fort and cost in areas where suitable materials are available. However, in
many areas of the nation, suitable soils have to be purchased and trans-
ported distances ranging from significant to prohibitive.
Some fine clays have liquid permeabilities as low as 10~8 cm/sec.7 A
layer of more common fine clay could have a permeability as low as 10 cm/
sec permeability^ but sandy silt is considerably more permeable. A per-
meability of 10" cm/sec is equivalent to 7.5 cm (3 in) of water seepage
per day. The California State Water Resources Control Board requires a
minimum permeability of 10" cm/sec for a site receiving decomposable (or-
ganic) materials.
Table 27 lists permeabilities of some soils and clays. For soils
available in the immediate vicinity of the landfill, the cost of installing
the barrier is similar to a normal grading operation, which averages be-
tween $1.96 to $2.62/cu m($1.50 to $2.00/cu yd). For a 15 cm (6 in) layer
of soil, the cost would be approximately $.36/sq m ($.30/sq yd). Importa-
tion of suitable soils over even a fairly short haul distance could double
the cost of installing the barrier.
When materials must be imported, commercially produced soil sealants
or plastic film barriers might become cost competitive alternatives. Com-
mercially processed bentonite clays which expand considerably when wetted
are available in powdered or granulated form. Mixing this material with
normal soils can produce a very low permeability material. For a 15 cm
(6 in) layer, sealant at 10 to 15 kg/sq m (2 to 3 Ibs/sq ft) would be re-
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TABLE 27. PERMEABILITY COEFFICIENTS FOR SOILS OF DIFFERENT TEXTURE
Material Permeability coefficient (cm/sec)
Coarse sand 1.39 x 10"
Sand 1-39 x 10~2
Fine sand 5.6 x 10
_3
Very fine sand 2.8 x 10
Loamy sand 1-4 x 10"
-4
Sandy loam 2.8 x 10
Loam 5.5 x 10"
Clay 1.4X10'6
Source - Reference 29.
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quired. Installed costs of American Colloid Company's VOLCLAY product
range from $1.79 to 2.39/sq m ($1.50 to $2.00/sq yd). A protective layer of
soil would be required above the barrier in most cases because this barrier
is not very resistant to physical forces resulting from vehicle traffic,
precipitation or drainage water. A suitable protective layer, using a
variety of materials, could be installed at normal grading costs of about
$.36/sq m ($.30/sq yd); thus, the total barrier cost ranges from $2.15 to
$2.75/sq m ($1.80 to $2.30/sq yd).
The permeability factors discussed above are for water percolation.
Gas has an even greater capacity for permeating soils than does water. How-
ever, since landfill gas is much less dense than water and slightly lighter
than air, it is more likely to migrate upwards if this is the path of grea-
ter permeability. Typical compacted solid waste.has a permeability range
(depending upon moisture content) of 10"J to 10"^ cm/sec, considerably more
permeable than a good soil barrier. If allowance is made for upward migra-
tion so that the downward pressure gradient does not become large (which
would be the case for a landfill gas recovery system), suitable liquid-soil
barriers should be able to prevent passage of the gas.
Another approach to a low- permeability membrane is a synthetic film
liner. Polyethylene (PE), chlorinated polyethylene (CPE), chlorosulfo-
nated polyethylene (hypalon), polyvinyl chloride (PVC), butyl rubber, and
ethyl ene propylene rubber (EPDM) are some of the more common materials used
for liners. The procedure used when installing a membrane is as important
as selecting the membrane material. Preparation of the base, seam joining
of membrane strips and application of a protective cover layer are all cri-
tical to the effectiveness and life of the membrane. If seaming of membrane
strips is performed by qualified personnel using the proper equipment and
procedures, the base material is free of rocks and debris, and care is taken
not to puncture the membrane while placing a protective layer of sand or
clean soil over it, any of these membranes will prevent liquid and gas
penetration for substantial hydrostatic heads and gas pressures. In addi-
tion, a membrane material should be selected that will not be affected bv
landfill leachate.
Table 28 lists costs of landfill liner materials. The cost of install-
ing membranes is considerably higher than soil barriers. Estimates ranqe
from $1.55/sq m ($1.30/ sq yd) for 10 mil thick polyethylene film (minimum
I^J^oo/5 ?£;00/sq m ($5.00/sq yd) for 30 mil butyl. A range of $2.15
to $3.23/sq m ($1.80 to $2.70/sq yd) installed has been estimated for 20 mil
polyvinyl chloride, a commonly used membrane material. This does not in-
clude the cost of base preparation or the protective layer above the membrane.
f i a]?w: Permeability barrier enhances environmental protection aspects
of a landfill by minimizing both gas and leachate migration. The cost-
benefits of a barrier, however, need to be weighed against the additional
gas revenues that would be gained as a result of the additional LFG re-
covered.
H n,hA 5y?f5et1^i la!?d!111' 40 ha (10° ac) in area> with an average fill
depth of 15.2 m (50 ft) is used for an approximate cost-benefit analysis.
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TABLE 28. COST FOR VARIOUS SANITARY LANDFILL LINER MATERIALS*
Installed costt
Material ($/sq m)
Polyethylene (10 - 20$ mils I) 1.51 - 2.42
Polyvinyl chloride (10 - 30$ mils) 1.96 - 3.61
Butyl rubber (31.3 - 62.5$ mils) 5.44 - 6.70
Hypalon (20 - 45$ mils) 4.82 - 5.12
Ethylene propylene diene monomer
(31.3 - 62.5$ mils) 4.07 - 5.73
Chlorinated polyethylene (20 - 30$ mils) 4.07 - 6.63
Paving asphalt with sealer coat (5 cm) 2.01 - 2.85
Paving asphalt with sealer coat (10 cm) 3.93 - 5.44
Hot sprayed asphalt (4.53 L/sq m) 2.51 - 3.35
Asphalt sprayed on polypropylene fabric (100 mils) 2.11 - 3.13
Soil-bentonite (24 kg/sq m) 1.21
Soil-bentonite (47.7 kg/sq m) 1.96
Soil-cement with sealer coat (15 cm) 2.09
* Source: Haxo, H.E. Jr. Evaluation of liner materials. U.S. EPA
Research Contract 68-03-0230. October, 1973. Adjusted to 1977 $.
t Cost does not include construction of subgrade nor the cost of earth
cover. These can range from $1.18 to $1.97/sq m/m of depth.
$ Material costs are the same for this range of thickness.
1 One mil = 0.001 inch = 0.0254 mm.
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Assumptions used range from conservative to optimistic. Assuming 474 to
710 kg/cu m (800 to 1200 Ibs/cu yd) in-place density of waste and 156 to
312 std cu m of LFG recovered per metric ton (5000 to 10000 scf/T) of waste
emplaced during the economic collection period, the total generation of
methane at 45 percent to 55qpercent concentration would be from 1.7 x 10
to 6.2 x 10 cu m (5.9 x 10 to 2.2 x 10 u scf) of methane assuming a 75
percent recovery efficiency. Placing an impermeable barrier below, on the
sides and on top of theolandfill could increase the yield to 90 percent or
from 2 x 10 to 7.4 x 10° cu m (7.0 x 10p to 2.6 x 1Q1U scf) of methane.
This incremental yield of from 0.34 x 10 to 1.1 x 10 cu m (1-2 x ]Q9 to
4 x 10 scf) of methane at $2.00/37.32 MM kJ (MM BTUs) would provide addi-
tional revenues of between $2.3 and $8.6 million.
The costs for a low-permeability barrier would be as low as $.36/sq m
($.30/sq yd) where good quality clay was readily available within (or adja-
cent^to) the landfill and as high as $3.95/sq m ($3.30/sq yd) for a high-
quality membrane at a site which required considerable base preparation.
For the 40 ha (100 ac) landfill example, 93645 sq m (112000 sq yd) of bar-
rier would be necessary to line the sides and bottom for a cost range of
$33,000 to $370,000. (Note that this range would be higher for a shallower
landfill and lower for a deeper landfill because the ratio of barrier area
to landfill volume is higher and lower, respectively.
Thus, it appears that there may be substantial economic benefit due to
increased LFG recovery.
Moisture Control
Although placement of a low permeability barrier as the final cover
layer prevents or reduces LFG losses by vertical migration, this approach
tends to prevent moisture infiltration. Data presented in Section 4 sug-
gests that a minimum of 50 percent moisture content is needed to enhance
gas generation. A low permeability cover thus, may retard LFG generation
by preventing needed moisture from reaching the active fill areas. Methods
for preventing gas escaping through the cover barrier while at the same time
allowing moisture infiltration, is therefore an item of primary concern.
There are three basic methods for allowing moisture infiltration while
preventing gas exfiltration. Use of a water distribution system to intro-
duce water below the low permeability soil or membrane barrier is one ap-
proach. A second approach is to use a soil barrier that will allow water
to infiltrate but will prevent gas migration. The third approach involves
overdesigning the gas collection system to prevent migration without the
need for a low permeability barrier. Each method is discussed and evaluated
and a cost-effectiveness example presented.
A water distribution system to introduce water below the low permeabili-
ty soil cover or membrane is a positive and readily controllable method for
providing moisture to a landfill. The distribution system resembles a field
crop irrigation system with main supply lines passing through the cover at
certain locations to connect to a system of distribution piping located
immediately below the cover. A key design problem for this type of system
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is the method used for sealing the main line penetrations through the cover.
Boots with sufficiently large flange areas and positive clamps to seal the
boot around the pipe have proven adequate in similar applications.
Both the cost and the effectiveness of water distribution depend on
the degree to which the distributed wastes are effected. Achieving an even
water release pattern without concentrated wet spots requires closely spaced
release points and thus a large quantity of piping. The optimization of
cost and effectiveness of the system is the major design requirement.
A distribution piping system consisting primarily of 2.5 and 5 cm (1 in
and 2 in) polyvinyl chloride (PVC) pipe costs approximately $4.10/m ($1.25/
lin ft) for pipe and installation. For a hypothetical fill area of 40 ha
(100 ac) distribution pipe lines spaced 15.2 m (50 ft) apart with 1750 de-
livery heads located 15.2 m (50 ft) apart, would require roughly 27430 m
(90000 ft) of pipe costing about $112,000. At an installation cost of $.20
per delivery head, the cost of the heads would be insignificant compared
to the pipe cost. With a high impermeability cover, evaporation losses
would be low and water quantity and pump requirements would be small. Pump-
ing costs would therefore be insignificant compared to the piping. A total
cost of $125,000 has been estimated for a 40 ha (100 ac) area using this
approach.
A semi-permeable soil barrier kept moist is another approach to con-
trolling the passage of water and gas. If a silty or sandy soil is kept
near moisture saturation, it would constitute a form of barrier to the out-
ward migration of landfill gas because the water fills the voids between
the soil particles. Although gas under sufficient positive pressure would
still be able to escape through the soil cover, using this approach in con-
junction with adequate gas withdrawal negative pressure should prove effec-
tive. The saturated soil would allow rainfall or artificially distributed
water to pass through but act as a barrier to gas passage.
In order to keep the soil layer saturated it would be helpful to treat
the soil with a humectant. Commercially available humectants in liquid or
powder form are often used in landscaping projects to improve the moisture
retention of the soil for plant irrigation purposes and in grading projects
to improve the ability of water to penetrate the soil for compaction pur-
poses Spraying approximately 61 1/ha (40 gal/ac) of humectant results in
a soil layer that has good water retention characteristics. One vendor pro-
vides a product at a cost of $.80/1 ($3.00/gal). It is possible to apply
this humectant to a 40 ha (100 ac) site for about $12,000 plus a modest
labor cost. The bulk of the cost of this approach would be in keeping the
cover soil saturated to make up for evaporative losses. This would require
an irrigation system costing $50,000 to $100,000 or the use of several water
trucks at a cost of about $150 each per day. The practical effectiveness
of this approach is limited, particularly in dry areas of the country. As
soon as a portion of the cover becomes dry, gas would escape from the land-
fill at that point.
The third approach consists of "pumping" the landfill in a manner which
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develops a slight negative pressure immediately below the cover. This would
allow the use of permeable cover for water infiltration. However, it is
difficult to control gas pressure with required precision over large areas,
and to prevent excess negative pressures in some areas from drawing in air.
This is particularly true if the landfill is relatively shallow. The area
of influence of a gas well approximates a pear-shaped sphere in configura-
tion. The radius of influence of the well in the horizontal plan is direct-
ly related to the depth of influence in the vertical plane. If a well is
pumped enough to influence a large area in the horizontal plane, the verti-
cal influence will be large and the well must be relatively deep to avoid
ingesting air from above the permeable cover. Thus, a large number of
closely spaced wells pumped at a moderate rate to recover all the gas and
pervent vertical migration is required. In addition, the sides of the land-
fill would have to be lined to prevent ingesting air from natural soil be-
yond the edge of the landfill.
Using the hypothetical 40 ha (100 ac) 15.2 m (50 ft) deep fill area
landfill, the required spacing of the wells can be determined as a function
of the radius of influence of the wells. The radius of horizontal influence
of recovery wells will vary from landfill to landfill with the permeability
of the waste. Solid waste permeability depends on composition, degree of
compaction, and typically is about 0.001 to 0.0001 cm/sec which is about
that of loamy sand. The design of the well, the depth of the fill and the
amount of vacuum applied also determine the radius of influence. For the
purpose of this estimate, the horizontal radius of influence that will
avoid air intrusion is taken to be 22.9 m (75 ft) for a 12.2 m (40 ft) deep
fill. Thus, the wells would have to be located on about 45.7 m (150 ft)
centers. 196 wells would be needed to completely cover the landfill. The
hypothetical landfill would produce about 45.8 cu m/min (1620 cu ft of gas/
min), based on 15.6 cu m/min/MM t (500 cu ft/min of gas/MM T) of in-place
waste. Thus, each well would be delivering about 0.28 cu m/min (10 cfm) of
LFG. The possibility of air intrusion or the existence of small pockets of
aerobic decomposition would still not be totally eliminated.
To put this collection system in perspective, the same landfill using
a low permeability cover material such that air infiltration would not be a
problem, could be expected to have a horizontal radius of influence for each
well of 30.5 m (100 ft). Locating the wells on 61 m (200 ft) centers would
result in 100 wells each producing about 0.45 cu m/min (16 cfm). The dif-
ference in cost of the two systems would be substantial. A 12.2 m (40 ft)
deep well costs from $2,000 to $4,000 to drill and install. Collection pip-
ing costing approximately $23/m ($7.00/ Tin ft) is required for the multiple-
well system. The total costs for the two systems, 100 and 196 wells, would
be about $465,000 and $810,000 respectively, a difference of $345,000.
For the 40 ha (100 ac) 15.2 m (50 ft) deep fill, the first method would
cost about $115,000, the second method $50,000 to $100,000 for a distribu-
tion system or about $500,000 per year for water spray trucks,and the third
method about $345,000 more than the well system that otherwise would be re-
quired.
The increase in gas generation expected to result from maintaining
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waste moisture at or above 50 percent compared with the typical solid waste
moisture content of 15 to 25 percent as emplaced cannot be estimated with
adequate accuracy because information is lacking on this subject. It is
clear, however, that increased moisture content results in enhanced gas
generation. An approximation of the cost-effectiveness of any of the three
measures can be made. Assuming a total gas generation quantity between 156
to 312 std cu m/t (5000 and 10000 scf/T) of emplaced solid waste, 474 to
710 kg/cu m (800 to 1200 Ibs/cu ft.) implace density; increasing re-
covery effectiveness from 75 to 90 percent would produce incremental gas
sales revenues between $2.3 and $8.6 million (same example used in the pre-
ceding subsection). Thus, all but the spray truck method would be cost-
effective in this example, even at the lower end of the additional revenue
range.
Leachate Collection and Recycling
Collecting and recycling leachate back into the fill is another pos-
sible way to control and maintain adequate moisture content and control
the pH to enhance gas generation. A pH range from 5.5 to 9.0 is generally
acceptable for gas production, but optimal pH is near 7.0 so that 6.0 to
8.0 probably is a more desirable range. Recycling the leachate would tend
to provide nutrients to the gas generating organisms, maintain desired pH
on a more even level throughout the fill as well as help maintain the de-
sired moisture level.
Leachate recycling is analogous to activated sludge being fed back into
the aeration tank influent in a sewage treatment plant.
An integral part of the leachate recycling system would be monitoring
of leachate composition and pH. In order to maintain pH within the desired
range, it may be necessary to add acidic or alkaline substances compatible
with anaerobic methane formers, or remove by appropriate treatment, any
components detrimental to gas formation.
The landfill fill area should be designed for leachate collection and
removal. In addition, a suitable irrigation distribution pipeline for
maintenance of moisture levels would be needed although probably not as
capacious a system and thus not as costly. Details of leach|te recycling
and appropriate treatment can be found in a 1975 EPA report.
Gas Recovery Well Design and Spacing
The first step in the design of a landfill gas recovery system is to
survey the landfill or its completed areas to determine if LFG is being
generated. This can be done by using portable methane sensing instruments
or by encapsulating air samples immediately above the cover material and
subjecting them to standard gas analysis procedures or a gas spectrometer.
The next step is to sink test probes at strategic locations in the fill to
collect LFG samples, undiluted by air, for methane and carbon dioxide analy-
sis as well as for other constituents. If reasonably accurate annual re-
cords of solid waste emplacement within general areas of the landfill are
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not available with at least approximate composition or source, it may be
necessary to obtain waste samples at various locations by taking shallow
and deep borings. The purpose of the gas and waste sampling and analysis
is to make certain that the landfill can be expected to generate gas at a
high enough rate over an extended period of time to make gas recovery practv
cal and economically viable.
One or more test wells should be sunk and operated at different vacuum
levels to determine LFG flow rates with gas samples analyzed to determine
the optimal suction pressure the fill can support without ingesting air in-
to the waste. Based on the maximum negative pressure that can be supported
by the cover material and the waste permeability, the radius of well in-
fluence can be calculated and plans for the wells and collection system
prepared. Wells should be no deeper than about 80 percent of the fill depth
and constructed as depicted in Figures 21 and 22. More details on well de-
sign and spacing are included in the ceoorts on the Palos Verdes, Mountain
View and Shelton-Arleta projects. ''
LANDFILL OPERATIONS
There are a number of operational techniques that can be considered for
potential enhancement of LFG generation that do not constitute design fea-
tures per se, although the addition of water for maintaining desirable mois-
ture content of the waste requires proper collection and removal of lea-
chate whether recycled or not. Such techniques include the initial appli-
cation of water to bring as received waste to the desired moisture level
during spreading and compaction; shredding to increase surface area,
achieve greater compaction, and possibly eliminate the need for daily cover;
seeding with sewage sludge to accelerate growth of bacterial colonies;
measuring pH of recovered leachate and adding substances to achieve desired
pH before recycling; and using a highly permeable daily cell cover that will
not significantly impede upward LFG migration.
Each operating technique is briefly discussed and evaluated according
to available information, together with cost estimates and potential cost-
effectiveness of those for which information is available.
Single Hater Application
Another possibility for providing the moisture necessary to enhance
gas generation is to add the required amount of water at the time the refuse
is placed in the landfill. Moisture content of solid waste as received
generally ranges from 15 to 25 percent. Water will have to be added to
bring this to a level between 50 and 60 percent. The use of a water truck
or, if feasible, a less expensive system consisting of hoses with spray
nozzles and one or two laborers generally is all that is needed to wet
down the waste after spreading. An increased operational cost of $100 to
$150 per day ($30,000 to $47,000 per year) would result based on six day
operations.
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Connecting
Valve Box
o"
fOO
Rubber Couplings
(to provide flexibility)
PVC Header Pip*
-size for system
flow
»
/Gravel level should
be a minimum of 4'
above first perforated
section
4"PVC pipe
To prevent grovel entry
wrap all Joints with
Burlap pnd fasten
With wire
Wire
PVC Ring cemented
to end of 4" PVC pipe
6"PVC pipe-
GRAVEL TYP. JOINT DETAIL
ill
30"Dio.
bore
Figure 22. Palos Verdes Landfill gas collection well and telescoping pipe configuration design.
105
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Refuse Shredding
Because shredded waste has a greater surface area to volume ratio than
raw waste it may be more susceptible to biological processes and conceiv-
ably could generate LFG at a greater rate than raw waste, ^oreover, it is
reported that shredded waste does not require daily cover. Costs of
shredding refuse vary from about $5.50 to as much as $16.50/t ($5.00 to
$15.00/T). If shredding is performed as part of the landfill ing opera-
tion, its cost must be recovered from increased LFG production. If done
as part of a resource recovery process, then the shredded waste is a by-
product and does not increase the cost of the landfilling operation.
In landfill operations in which only a portion of the incoming waste is
shredded, the LFG generation rate might be enhanced by placing the shredded
material in thin layers distributed throughout the unprocessed refuse. The
shredded waste is believed to act as a seed material layer for accelerated
microbial growth. Use of shredded waste is reported to obviate the need
for daily cover which would enhance LFG collection and possibly permit
greater spacing between adjacent recovery wells. However, no data is avail-
able that permits an evaluation of the effectiveness of this technique com-
pared to its costs.
Use of High Permeability Cover
The placement of daily cover results in the landfill developing as a
series of separate waste cells. This cover, if of low permeability soil,
can prevent or retard the movement of moisture, methane forming bacteria
and nutrients, resulting in reduced LFG generation. The daily cover can
also retard movement of LFG within the influence area of the well, requiring
greater negative pressure and causing air ingestion at the surface. However,
the many benefits of daily cover make it generally undesirable to eliminate
it from a landfill operation. Daily cover is necessary to reduce odors,
disease vectors, rodents, litter, aesthetic impact and many of the other
potentially negative aspects of a landfill.
Alternative approaches are the use of high permeability cover material;
or the removal on the interior daily cover just prior to each successive
lift being placed. The landfill then ultimately would consist of a single
large cell rather than a series of many small cells.
It has been observed during the drilling of wells in some deep landfills
that had been constructed using a permeable cell cover that no evidence of
cell structure or cover material layers were evident. This was attributed
to the sifting of the cover soil through the refuse as a result of vehicu-
lar traffic vibration and water transport. The cost would be small unless
the permeable cover material had to be imported. There is no information
available on the effects of these techniques, so cost-effectiveness cannot
be estimated.
Sewage Sludge Seeding
Spreading raw or digested sewage sludge atop each landfill cell before
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spreading the daily cover conceivably could hasten the generation of LFG.
However, it is also possible that exposure of sludge to the air during
spreading could impair activity or even kill the bacteria colonies such
that no advantage whatever is obtained. Until more specific research and
test results on this technique become available, its potential value cannot
be judged.
Leachate Recycling with pH Control
This technique was discussed in the subsection on design under leachate
recycling. When leachate collection and recycling is included in the land-
fill development, it requires little more equipment or expense to periodi-
cally sample the leachate and modify its pH. Until more specific data is
obtained on the precision with which pH control should be applied and the
ramifications of different pH values on the rate of LFG generation, the
applicability of this technique cannot be evaluated.
SUMMARY
Table 29 lists in summary form alternative design and operations tech-
niques that could enhance LFG generation. Obviously, the design techniques
apply only to new landfills or the sections of established ones that have
yet to be filled.
Among the alternative approaches to site lining (bottom and sides),use
of impervious soil, if available, is by far the lowest cost material that
would be needed to prevent leachate percolation into the ground water table
whether LFG recovery is included in the landfill development or not. If
suitable low permeability soil must be imported, the distance will determine
the degree of competitiveness with other alternatives such as clay treated
on-site soil. Use of a reliable film barrier requires careful placement
that can be several times more costly than impervious soil, as is also the
case with sealant covered asphalt cement which can be used only over a
highly stable base.
Among moisture control techniques, leachate collection and recycling
appears competitive with water distribution below the top cover and is to
be preferred if permitted by local water quality control regulations.
Usually, where it can be demonstrated that the possibility of leachate
seeping through the bottom lining is virtually negligible, this approach
is likely to be permitted.
Concerning the operations alternatives, there is insufficient informa-
tion available with which to make evaluations or even postulate probable
effectiveness. If water loss with LFG is substantial, then a one time addi-
tion of water to the waste prior to daily cover is likely to be insufficient
over the long term. The subject of waste shredding prior to landfill ing
has been in contention for some time and at best its benefits are not likely
to offset its high cost. Use of a permeable daily cover that will temporar-
ily prevent vector attraction but permit moisture and gas passage can be
effective in reducing landfill gas internal flow resistance, but will not be
107
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TABLE 29. DESIGN
AND OPERATIONS ALTERNATIVES FOR LANDFILL GAS
GENERATION ENHANCEMENT
Alternative
Potential effectiveness
Cost range
($/sq m)a
Site Lining
Impervious soils
Treated soils
Film barrier
Asphalt cement
with sealant
Moisture Control
Water distribution
below cover
Semi-permeable soil
with humectant
Controlled uniform
negative pressure
below cover
Leachate Collection
and Recycling
Effective if permeability low
Effective if permeability low
Effective with proper base pre-
paration and cover protection
Effective if properly installed
on firm base
Highly effective
Effective if kept moist
0.25 to 0.42
1.50 to 1.92
1.05 to 4.60
3.00 to 4.05
0.21 to 0.42
0.03 to 0.04
(add 1,00/yr/sq m
operating cost)
Effective if carefully balanced 0.63 to 0.84
by wells with half normal spacing (additional cost
for recovery sub-
system)
Effective; pH control may be
required
0.13 to 0.29
plus cost of
neutralizing
chemicals
Operations
Single water appli-
cation (truck or
hose/spray nozzle)
Waste shredding
without daily
cover (final
cover only)
Permeable daily
cover
Sewage sludge seed-
ing of waste
Leachate recycling
with pH control
Effective initially; long term
affects unknown
Affects unknown; may hasten
initial LFG generation and
should increase waste perme-
ability
Increase ease of movement of LFG
within confines of landfill
Affects unknown; may shorten LFG
generation initiation time
Effective
0.02 to 0.03
4.18 to 8.63
per ton received
No additional
cost if suitable
soil available
0.25 to 0.42
(drop charge may
exceed spreading
costs)
0.13 to 0.29
plus cost of
neutralizing
chemicals
a Costs estimated for 40 ha (100 ac) fill area landfill.
108
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very effective in preventing odors from eminating from the cell.
The effect of seeding solid waste with sewage sludge is not known at
present and until controlled tests can be constructed, this technique can-
not be evaluated. Leachate recycling with pH control is listed under both
operating techniques and design approaches because it requires special
facilities to be designed and constructed in the landfill from its incep-
tion.
Overall, the results of this evaluation emphasize the need for more
definitive data and information on moisture effects and interactions on gas
recovery. All that can be stated at this time is that, as indicated in
Table 29, several of the design and operations techniques are estimated to
be reasonable in terms of cost provided an appreciable increase in LFG re-
covery rate, on the order of at least 10 percent, results. To make this
determination, carefully designed and controlled full scale experiments
appear to be required. This subject is more fully discussed in the next
section.
109
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SECTION 7
PROJECT SUMMARY - RESULTS, CONCLUSIONS AND RECOMMENDATIONS
This section brings together and discusses in more detail the findings
and conclusions of this study on the state-of-know!edge of landfill gas gen-
eration, processing and utilization. It concludes with recommendations for
research for demonstration projects needed to develop the necessary addi-
tional data or refine existing information in order that the technical and
economic feasibility of LFG to energy conversion systems can be clearly
established.
RESULTS AND CONCLUSIONS
The results and conclusions deal primarily with the adequacy of basic
data on gas generation, approaches and techniques for optimization of gas
generation and recovery, and the costs and economics of LFG system alter-
natives compared with other waste-to-energy process systems.
Basic Data Adequacy
Evaluation of the data available on landfill gas generation phenomena
reveals a dearth of hard empirical data on such basics as theoretical and
practical gas generation rates and total quantity of gas that can be ex-
pected per unit quantity of typical solid waste, or on an organics content
basis. The very nature of anaerobic decomposition of organic materials in
landfills over long periods of time after waste emplacement makes this dif-
ficult. It is fairly well established that methane (together with carbon
dioxide) generation rate increases rapidly during the first 3 to 12 months,
diminishes gradually from the maximum rate over a period of 5 to 10 years,
and then diminishes more rapidly during the declining period that may last
an additional 10 to 30 or more years.
Gas generation depends upon numerous variables such as waste composi-
tion, moisture content, cell structure, landfill depth and internal tem-
perature. Consequently, simulation or replication of landfill processes
are difficult and expensive to reproduce in the laboratory under conditions
in which variables can be controlled, or, at least measured. Although
chemical-physical analytical models of the multi-stage decomposition pro-
cess have been developed, knowledge of the maximum quantity of gas generated
per unit of refuse is based on only theoretical calculations. This is be-
cause almost all organic waste materials are comprised of some relatively
inert or biologically refractory material which resists decomposition and
is not completely digested or, if so, only very slowly.
110
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While analogies have been made to model controlled environment, bio-
digestion of solid waste and 5 to 10 percent sewage sludge in a water slur-
ry (a process that proceeds virtually to completion within about 30 days),
only maximum gas production rates and total unit quantities have been de-
duced. Because the landfill environment is markedly different from the
waste-sludge-water slurry digester tank, the maximums cited are unlikely to
be realized in a landfill environment.
Composition of landfill gas, however, is well established because this
is a relatively easy measurement once wells have been sunk and stable gas
generation conditions have been established. Even so, reliable LFG com-
position data ranges from about 45 to 60 percent methane; the remainder
being carbon dioxide with small amounts of nitrogen, oxygen, hydrogen sul-
fide, other trace gases, and water vapor at the gas saturation level. The
factors that influence methane content of landfill gas are not precisely
known at this time due to imprecise data on quantity and variation of waste
composition amoung the numerous cells of the landfill or even within the
area of influence of a single gas recovery well.
This lack of a reasonable level of certainty or confidence in the ba-
sic data upon which the economics of landfill gas recovery and processing
systems are based is one major factor deterring progress in implementation
of such systems.
Gas Generation and Recovery Optimization
Several alternative design approaches and operating techniques for
optimizing gas generation and recovery have been discussed (Section 6),
although only in qualitative rather than quantitative terms because of the
lack of data on which to base quantitative estimates. While gas migration
control is compatible with optimization of gas recovery, there are numerous
unknowns or uncertainties regarding use of non-permeable bottom and side
barriers to gas flow in terms of effects of higher gas partial pressures
and possible greater concentrations of metabolic wastes or gases (e.g.,
hydrogen) on methanogenic organisms. An optimal surface cover material for
landfills with gas recovery is one that permits infiltration of water and
prevents passage of gas. However, experimental or empirical data that
would permit selection of the most cost-effective methods are not available.
Optimum moisture content of the emplaced waste to maximize gas genera-
tion, related loss of moisture (water vapor in the recovered gas and
evapotranspiration), moisture produced by the bacterial organisms, together
with the amount of water that may have to be added to maintain maximum gas
generation cannot be addressed in specific quantitative terms. However,
methods for controlling moisture content of the waste prior to emplacement
in the landfill and methods for adding water thereafter have been evaluated.
Leachate control and possible recycling have some merit. When leachate
is prevented from percolating into underlying ground water either by locat-
ing landfills at sites with underlying impermeable geological structures or
by placement of artificial barriers, downward migration of landfill gas, in
m
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all likelihood is simultaneously prevented. This is particularly true if
the bottom material, when wet, becomes impervious to gas passage, or an arti-
ficial barrier material is used that is impervious to gas passage. The use
of recovered leachate to maintain moisture levels in emplaced solid waste is
another approach discussed and evaluated for applicability and cost. How-
ever, the influences of both pH control and leachate recycling on methane-
forming organisms is not adequately known although the preferable range of
pH that is believed to enhance methane formation is known (see Section 4).
The entire subject of pre-processing or preparation of solid waste pri-
or to landfilling to maximize gas generation, in terms of rate, total quan-
tity per unit quantity of waste, and methane content, is open to supposi-
tion. There may be some improvement in gas generation rate resulting from
shredding waste prior to emplacement due to potentially greater surface
exposure to methanogenic organisms. Because of the relatively high cost of
shredding, however, the resulting increase in revenues may not be sufficient
to pay for the pre-processing. However, the revenues from the recovery and
sale of metals and glass (which normally requires shredding) might totally
or substantially cover shredding costs such that pre-processing becomes
economically viable. Whether removal of metals from the waste will enhance
methane generation (by eliminating most of the metallic oxides which may
deter methanogenic processes directly of indirectly by decreasing pH values)
also is not known. There are obviously numerous factors involved in the
analysis and selection of techniques for enhancing methanogenic processes
that remain uncertain.
The cost and economic analyses presented in Section 5 show that recov-
ery and use of landfill gas in its raw state, or processes to remove water
vapor.or both water vapor and carbon dioxide, can be economically viable
even with gas generation rates, total quantities and composition toward the
low ends of the quantitative ranges. Thus, improving the level of know-
ledge and reducing uncertainties in these areas is likely to contribute
most to avoiding those complex and expensive processing and utilization
alternatives which, based on existing data, promise a lower and more mar-
ginal return on investment. Emphasizing the need for better information in
these areas is the apparent fact that market potential for upgraded landfill
gas near or equal to the heating value of natural gas, or steam or electric-
ity generated using unprocessed landfill gas, generally is considerably
better than for raw gas.
Cost and Economics
The cost and economic analysis contained in Section 5, in general, is
based on mid-to-low range estimates of landfill gas quality and a conser-
vative ten-year period of gas generation at rates that warrant recovery and
processing. For the simplest processes and those that employ direct utili-
zation of recovered gas (which also have the lowest costs and most favor-
able economics), it can be argued that more reliable and higher confidence
level data are not needed. However, because processing and utilization
equipment characteristically have intrinsic operating lives of 20 or more
years, the problem of justifying purchase and installation of equipment
112
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with a 20-plus year useful life for a landfill gas recovery project that
promises only a 10-year economic gas generation-recovery period will un-
doubtedly arise.
Consequently, a major uncertainty in the cost and economic analyses
centers on the period of useful gas generation. Useful is defined as
generating gas at a rate sufficient to warrant recovery by originally em-
placed wells, collection pipelines and pumping blowers or compressors with-
out substantial reduction in facility capacity. Overpumping the wells
would increase impurities in the gas (primarily nitrogen) or deter or cause
gas generation to cease due to oxygen poisoning of the methanogenic organ-
isms.
Another major uncertainty concerns gas recovery rate and composition
stability over time. The basic marketability of landfill gas in any form
depends upon ability to meet customer quality specifications and demand
over a relatively long term. No potential purchaser is likely to invest
in the necessary facilities to use substandard fuel gas unless there is
assurance of a reasonable number of years over which to amortize this in-
vestment. Moreover, unless an adequate number of years of landfill gas
use can be assured, the increased amortization rate may make use of this
gas uneconomical or noncompetitive with other fossil fuels or waste-to-
energy processes.
Obtaining more reliable basic data on the generation of landfill gas
and on optimization of rate and period of useful generation is virtually
mandatory in order for the potential of this fuel to be realized on a wide-
spread commercial basis. Additional research and development, and demon-
stration projects are needed to substantiate, if not improve upon, the
values selected and used in this study.
RESEARCH AND DEVELOPMENT, AND DEMONSTRATION PROJECT RECOMMENDATIONS
This subsection identifies and briefly discusses research, development
and demonstration projects on landfill gas generation, processing and
utilization believed necessary to eliminate uncertainties from the existing
body of information on the subject.
R&D demonstration needs were developed from assessment of the material
presented in Sections 4, 5, and 6 which essentially describe the existing
level of knowledge and state-of-the-art in recovery, processing and utili-
zation of landfill gas as a supplementary fuel. The material contained
in those three sections resulted largely from the review, study and analy-
sis of available literature, from unpublished information available to the
study participants either from their own projects or from those pursued by
others, and from additional analysis performed especially for this study
Only limited new basic information about landfill gas recovery, processing
and utilization has been developed during this study because its emphasis
was^to pull together, analyze and refine existing information, perform
additional analysis and present it in a concise, cogent and usable fashion
within the bounds of a single report. The review work performed, however,
113
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does suggest some new approaches and improvements to existing tehcniques
for optimizing landfill gas recovery, processing and utilization.
The major tenets underlying the R&D and demonstration projects sugges-
tions are existing and prospective markets for use of landfill gas as a
supplementary fuel in relatively widespread commercial and industrial appli-
cations. The diminishing supply of natural gas, increasing importation of
crude oil with its adverse international balance of payment ramifications,
and the similarity of landfill gas to natural gas in terms of its clean-
burning qualities all serve to increase interest in the potential for wide-
spread utilization. Based on recent experience with solid waste resource
recovery (materials and energy), the suggested projects are needed to une-
quivocably demonstrate the technological feasibility and provide the econo-
mic viability data required by both public and private entities before
widespread implementation ^f landfill gas recovery/processing/utilization
is likely to occur.
RESEARCH AND DEVELOPMENT NEEDS
The suggestions for research and development to improve basic landfill
gas generation and recovery data, and to optimize gas generation and re-
covery performance are representative of the work required in the near fu-
ture. No attempt has been made to design projects in detail or optimize
their potential payoff in meeting improved basic and new data requirements.
Although research and development reports and lists of ongoing EPA and DOE
projects have been taken into account, there may be work in progress that
will produce some or all of the needed data. If so, these suggestions will
confirm the value of such projects and perhaps validate further funding
that may be required for their completion.
Table 30 lists suggested landfill gas research and development pro-
jects by title, objectives, and gross estimates of project duration and
direct professional labor by work category. Each project is briefly dis-
cussed below in terms of need, objectives and techniques involved.
1. Improved baseline Data Development for Landfill Gas Generation
and Recovery
Basic data on landfill gas generation in terms of gas generation
rate, gas composition (initially and over time) and total quantity
of gas (particularly the methane content) produced per unit of
total waste or organic components are imprecisely known. These
gas characteristics are basic to unraveling the costs and econo-
mics of gas recovery/processing/utilization and dispelling exist-
ing uncertainties which presently tend to retard implementation
of gas recovery systems.
Objectives
To develop, by means of a combination of analytical models, labo-
ratory simulation, and full scale controlled tests, improved
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TABLE 30. SUGGESTED LANDFILL GAS RESEARCH AND DEVELOPMENT PROJECTS
Project title
1. Landfill Gas Gi
Project objectives Estimated duration
(months)
snera- Develoo reliahlp anH im_ Q +n 10
Estimated work content (person-months)
Analysis/design/reports Laboratorv work
Field work
3.
4.
5.
7.
, - '-wfiv.llULflCUlIU Jill'
tion/Recovery Improved proved basic data on gas
Baseline Data Develop- generation characteristics
ment
2. Landfill Gas Genera-
tion Optimization
Techniques Test and
Evaluation
Design experiments, test
and evaluate alternative
optimization techniques
Landfill Design Optimi- Determine most cost-effec-
zation for Gas Recovery tive design parameters for
(Existing and New Land- gas collection at existing
and new landfills includ-
ing geometry, depth, pol-
lution control.
Gas Recovery Well and
Collection System' De-
sign Optimization
Leachate Recycling and
other Liquids Use to
Enhance Landfill Gas
Generation
Improvements in
Energy Recovery
Efficiency of Land-
fill Gas Generation
Recovery
Benefits of Pre-
landfill Processing
for Improving Land-
fill Gas Generation
Determine best well con-
figuration, influence area,
spacing, pumping and col-
lection system
Test and evaluate leachate
and other liquid waste in-
troduction to increase gas
generation rate, quality, etc.
Develop, test and evaluate
methods to improve basic
energy recovery efficiency
(gas energy content vs
waste energy content)
Test and evaluate benefits
and costs of various pre-
landfilling waste process-
ing including inorganics
'recovery
12 to 18
8 to 12
6 to 9
8 to 15
8 to 12
8 to 12
6 to 12
6 to 12
6 to 12
8 to 12
4 to 8
6 to 12
8 to 12
3 to 6
6 to 12
1 to 2
1 to 2
4 to 6
6 to 12
4 to 8
3 to 6
6 to 12
6 to 12
6 to 12
6 to 12
6 to 12
(continued)
-------
CT>
Table
30.
continued
Project title
8.
Refined
Cost
and
Project
Develop
objectives
refined
costs and
Estimated duration
(months)
4 to 6
Estimated work content (person-months)
Analvsis/desiqn/reports Laboratory work
10 to 12
-
^^^^^^^""H*
Field work
-
9.
Economic Analysis
of Landfill Gas
Recovery/Processi ng/
Utilization
Handbook for Landfill
Gas Recovery/Process-
ing/Utilization
10. Evaluation of insti-
tutional Constraints
to Landfill Gas
Utilization
11. Evaluation of Equip-
ment Changes for
Utilization of Land-
fill Gas
landfill gas recovery, up-
grade processes and utiliza-
tions based on improved
baseline and optimization
data
Handbook covering basic
design, common variables
and operational informa-
tion
Analysis of deterrents to
use of landfill gas, in-
centives and other aspects
to encourage use
Determination of boiler,
furnace, gas turbine, gas
engine changes necessary
to use raw and processed
landfill gas including
costs and economics
6 to 9
6 to 9
6 to 9
6 to 12
6 to 8
8 to 10
-------
data on gas production rates, composition and variations over
time, and most important, the total amount of methane that can
be produced per unit of wastes or organics quantity over the total
or half-life of the process.
Techniques
Analytical models treating all relevant anaerobic decomposition
gas generation variables will be developed. Numerous samples ob-
tained from landfills of different ages where original waste compo-
sition is reasonably known should permit laboratory determination
of degree of decomposition as a function of time and moisture con-
tent in order to provide data for the models. Laboratory simula-
tion of the landfill decomposition process or full scale controlled
tests should provide additional data. Laboratory sample water-
slurry analogues may permit additional correlation with landfill
sample data. Accurate estimates of degree of decomposition and gas
characteristics over time can be established by a combination of
these analytical, sampling and laboratory simulation techniques.
A preliminary evaluation of techniques and their relationships is
advisable to assure a sound project.
2. Landfill Gas Generation Optimization Techniques Tests and Evalua-
tion
A number of techniques have been suggested that might prove useful
in improving landfill gas generation, such as increase and main-
tain a high moisture content, shred waste before landfilling, seed
solid waste with sewage sludge and recycle leachate, using chemi-
cal additives to control pH. This may improve digestibility of
certain organic waste components, shorten time to initiation of
anaerobic decomposition or significantly enhance gas generation
rate or quality of methane production.
Objectives
Conduct experiments using both laboratory simulation and full scale
landfill environments to test and evaluate, singly and in appro-
priate combinations, techniques to enhance landfill gas generation
which could lead to optimization of the use of one or a combination
of these techniques. Costs and benefits can then be evaluated
against resulting gas generation characteristics. Those techniques
that prove beneficial will be recommended for use.
Techniques
Use of laboratory simulation should be capable of discriminating
among alternative and competing optimization techniques by com-
parative measuring of gas generation rate, quantities and charac-
teristics even though simulation values may not precisely repli-
cate full scale landfill environments. Promising techniques can
117
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then be reproduced in limited full scale landfill test volumes and
results compared.
3. Landfill Design Optimization for Gas Recovery
Several possibilities for optimal design of landfills for gas re-
covery are discussed in Section 6 of this report. There is an
apparent need to perform more detailed theoretical analysis and
testing of these techniques, particularly the use of impervious
and permeable materials both to constrain gas and moisture, and
to permit controlled passage. Geometry of landfill cells and
methods to cause a landfill composed of numerous cells to perform
like a single waste deposit are also of interest. Leachate con-
trol and possible recycling of leachate also are techniques that
need specific experimentation.
Objectives
Further evaluate landfill design techniques analytically and test
and evaluate alternative methods for improving recovery effective-
ness, moisture control, well influence area effectivness, gas
pumping methods, etc.
Techniques
Development of landfill geometric configurations can be accom-
plished analytically. Experiments can be designed for laboratory
evaluation of permeable and impermeable material barriers to op-
timize moisture passage while minimizing gas penetration. Mechani-
cal disruption of cell barriers as a new cell is placed on top also
is of interest and requires full scale experimentation.
4. Gas Recovery Hell and Collection System Optimization
Analytical and experimental work is needed to optimize gas recovery
well design, area of influence diameter to depth relationships,
and proper landfill cell compaction to optimize well influence
areas and minimize both capital and operating gas recovery system
costs. Although existing wells appear to function satisfactorily,
their efficiency and effectiveness are not adequately known.
Objectives
Develop optimal landfill gas recovery well design as related to
waste composition, density and geometry, and influence area,
spacing and depth. Also, evaluate and select the best materials
of construction, pumping equipment, pressure monitoring probes, etc,
Techniques
Much of this project can be accomplished via analytical models and
118
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simulation. Equipment performance can be measured and compared
under test laboratory conditions in many instances. Promising sys-
tems can then be installed at full scale landfills and performance
measured both on an absolute and relative basis.
5. Leachate Recycling and Other Liquids Use to Enhance Landfill Gas
Generation
The possibility of recirculating landfill leachate for pH as well
as leachate control is discussed in Section 6. Other waste liquids
may have useful application for p'H and moisture control to enhance
gas generation. Little is known of the effects of alternatives
and experimentation appears to be required using both laboratory
simulation and full scale tests.
Objectives
Determine effects of leachate recycling on gas generating landfills
and the potential utility of other non-toxic liquid wastes for
either pH or moisture control, or both. Also, water-slurry bio-
digestion of solid wastes with a small percentage of sewage sludge
suggests that weak acid or alkaline hydrolysis may increase the
digestibility of cellulosic materials.
Techniques
Much of the work of this project can be accomplished in the labo-
ratory under carefully controlled conditions. Samples of typical
solid waste can be pretreated to determine if hydrolysis improves
gas generation quantities per unit of waste. Leachate and other
liquid wastes can be used on waste samples to determine effects on
gas generation. If techniques prove of value, then tests can be
conducted in controlled areas of full scale landfills.
6. Improvements in Energy Recovery Efficiency of Landfill Gas
Generation/Recovery
Techniques that can significantly increase the amount of energy
recovered as landfill gas compared with that originally contained
in the waste appear to be needed. Shredding and/or hydrolysis
of the waste prior to emplacement, seeding with sewage sludge dur-
ing emplacement, and removal of metals and most other inert ma-
terials prior to landfill ing appear to be other possibilities.
Objectives
Determine if certain types of waste pre-processing and pre-treat-
ment prior to or immediately after emplacement can increase recov-
ery efficiency; evaluate cost effectiveness of promising techniques.
119
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Techniques
Initial work can be accomplished entirely in the laboratory.
Waste samples can be prepared by alternative pre-processes and
landfill decomposition can be simulated by bio-digestion tests
which measure total gas generation and degree of decomposition.
Promising techniques can be further evaluated via full scale
landfill tests, with controlled emplacements of differently pre-
processed or pretreated wastes. Performance can be measured by
comparative analyses and waste composition as a function of age.
7. Benefits of Waste Processing for Improving Landfill Gas Generation
Improvement in the economic performance of LFG generation and
recovery systems appear to exist by removing non-biodegradable
materials from the waste prior to landfill ing. This approach
potentially improves the volumetric efficiency of. landfills for
more concentrated gas generation and reduces the number of wells
required to collect the gas because all or nearly all of the waste
emplaced will be organic. Also, revenues derived from recovery
and sale of metals and glass may reduce the cost of energy recov-
ery or cover the cost of otherwise uneconomic pre-processing.
Objectives
Study applicability of various pre-processing techniques for im-
proving economics of LFG production and recovery. Determine
economic advantages and disadvantages of pre-emplacement waste
segregation and recovery of inorganics to achieve more efficient
use of landfill space and more effective use of landfill gas col-
lection systems.
Techniques
Analytical results are to be verified through laboratory tests
and evaluations to the extent possible. Subsequent tests and
evaluations in limited landfill areas under controlled conditions
are suggested.
8. Refine Cost and Economic Data on Landfill Gas Recovery/
Processing/Utilization
Improved baseline data on landfill gas production and recovery,
together with information on optimization techniques for more effi-
cient systems, will permit more accurate preliminary system design
and cost estimating.
Objectives
Refine estimates of capital and operating costs for alternative
recovery, processing and utilization systems at various capacity
120
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levels or flow rates using improved baseline gas generation and
recovery performance data. Compare detailed economic analyses
of best alternatives with fossil fuel and other waste-to-energy sys-
tems.
Techniques
Preliminary design for complete landfill gas recovery, processing
and utilization alternatives at no less than three capacity levels
can provide the data for estimating capital and operating costs
over the useful life of the system. Curves of unit capital and
operating costs plotted as functions of capacity will illustrate
economies-of-scale. Economic analysis will allow prediction of
financial performance of alternative systems under varying market
conditions and pricing structures for recovered materials and
synthetic fuels. Sensitivity analysis will cover uncertainty in
fuel and materials prices for future periods.
9. Handbook for Landfill Gas Recovery/Processinq/Utilization
To foster widespread consideration and implementation of LFG
waste-to-energy systems, a detailed handbook on applications
analysis, and selection of most appropriate alternatives suitable
to specific local conditions would be most helpful. Also needed
are suggestions on market research and analysis, best uses for the
fuel, steam vs. electricity conversion, alternative methods for
financing capital costs, and split ownership arrangements with
utilities or large industrial/commercial energy users. This
handbook would parallel various other handbooks that have already
been prepared for solid waste resource recovery, incineration,
etc.
Objectives
Provide data, information, analysis techniques and suggestions for
conduct of feasibility studies, selection of system alternatives,
marketing and contracting for sale of products, system design and
construction, and operation of landfill gas recovery, processing
and utilization systems. Also to be provided are basic safety and
security techniques, storage methods for interruptable customer
deliveries, etc.
Techniques
Essentially, the handbook will be a compilation and analysis of
data and information presently available in the literature with
added explanation of techniques suggested and how to evaluate re-
sults. Dependent upon timing of handbook preparation, a series of
handbooks such as were prepared for resource recovery, could pos-
sibly be developed incrementally as additional data and information
becomes available.
121
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10. Evaluation of Institutional Barriers to Landfill Gas Utilization
Initial attempts to market dehydrated LFG and LFG upgraded to near
natural gas standards have been confronted with considerable re-
luctance on the part of potential users to contract for purchase
of this gas. Why potential industrial users are reluctant is not
precisely known, but the only current purchasers are two utilities
(Pacific Gas & Electric Company, Mountain View Projects; and
Southern California Gas Company, Palos Verdes Project) who are par-
ticipating in demonstration programs. Also, the Los Angeles De-
partment of Water & Power has contracted to purchase the landfill
gas from the Sheldon-Arleta Landfill. In the private sector, one
chemical company has signed a contract for purchase of dehydrated
gas from the Azusa-Western Landfill project. It is reported that
no firm sales of recovered LFG have yet been accomplished in other
areas of the nation.
Objectives
Determine why potential users are reluctant to purchase LFG and
what is necessary in the form of incentives, technical assistance,
reliability and quality guarantees, etc., to encourage purchase
and use. Recommend appropriate pricing policies, etc.
Techniques
Approaches which can be used include mail questionnaires directed
to large commercial, industrial and institutional fuel users, par-
ticularly those threatened with future reduction or cutoff of their
natural gas supply. Selected responses would be followed up with
interviews of plant engineers and corporate executives to discuss
what would encourage use.
11. Evaluation of Equipment Changes for Utilization of Landfill Gas
Use of any form of LFG usually requires certain modifications to
boilers, furnaces, gas turbines and reciprocating gas engines,
storage and compression systems, and possibly even distribution
trunklines of gas utilities.
Objectives
Determine required alterations to combustion equipment for use of
dehydrated and upgraded forms of LFG in typical steam generating
equipment. Prepare cost estimates for alterations to existing equip-
ment or required new equipment, and determine overall economics of
LFG use. Prepare advisory memoranda for suppliers and potential
users of landfill gas to help marketing efforts.
Techniques
Analyze combustion characteristics of different grades of LFG to
122
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determine fuel-air ratios, flame temperatures, flame propagation,
corrosion problems, storage and pressure requirements, and burner
characteristics. Determine necessary alterations and substitutions,
time required for modifications, and tests or "shake down" evalua-
tions that may be required and aggregated costs of such changes to
representative installations.
DEMONSTRATION PROJECT NEEDS
Current Activity
There are a number of major LFG recovery, processing and utilization
projects in various stages of development or operation in the United States
at the present time. Table 31 lists major projects on which some informa-
tion is available, although only one or possibly two were in regular com-
mercial operation at the end of 1977. Two additional projects are scheduled
to begin commercial operation in 1978 and the others are in various stages
of evaluation, planning or design. Only the Mountain View Landfill gas re-
covery project has received EPA monitary support, the costs being shared
with the Pacific Gas & Electric Company.
Of the three projects that have progressed either to the stage of com-
mercial operation or initial shake down operations prior to beginning regu-
lar operations, two (Mountain View and Palos Verdes) employ triethylene gly-
col water vapor removal and molecular sieve carbon dioxide removal to up-
grade the gas to near natural gas specifications. The third project at the
Azusa-Western Landfill only removes water vapor with triethylene glycol be-
fore delivery to a nearby chemical plant. The only other project that ap-
pears reasonably certain to be completed is the Sheldon-Arleta Landfill
facility sponsored (and owned) by the Departments of the City of Los Angeles
California.
Any one of these ongoing or soon to be in operation projects could
provide needed performance and operations data to establish the technical
feasibility of LFG recovery and processing to produce a dehydrated gas with
about one-half the heating value of natural gas or upgrade processing to
deliver a gas approximating the characteristics and heating value of nat-
ural gas. Certainly, cost and economic data will be available from the
Mountain View project partially funded by EPA, but whether or not similar
data will be made available on the Palos Verdes and Azusa-Western projects
is uncertain. Private industry typically is relucant to reveal details on
performance and economics lest they compromise their competitive position
or industrial secrets.
Demonstration Project Recommendations
_ Considerable factual data on the technological feasibility and econo-
mic viability of landfill gas recovery, processing and utilization is re-
quired before this waste-to-energy method can be expected to achieve wide-
spread application. In fact, several of the projects listed in Table 31
are understood to have been suspended awaiting "hard" favorable data from
initial projects.
123
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TABLE 31. MAJOR LANDFILL GAS RECOVERY/PROCESSING/UTILIZATION PROJECTS IN THE UNITED STATES
Mountain View
Landfill
Recovery System
Location and Gas Rate
Mountain View, 20 wells, average
Calif. fill depth 40 ft,
1 million scf/D
700 cfm
Processing System
Compression of 400 psig
Triethylene Glycol
water removal and
Molecular Sieve carbon
dioxide removal to pro-
duce 750 BTU/scf gas
Status and Utilization
Scheduled to begin opera-
tion by end of 1977
Gas to be introduced into
PG&E natural gas trans-
mission line resulting
in 975 BTU/scf mixed gas
Sponsors/Owners
City of Mountain
View, Pacific
Gas & Electric
Co. with EPA
grant for par-
tial funding
Palos Verdes
Landfill (CA Class
I)
Azusa-Western
Landfill
Rolling Hills 8 wells, average
Estates, Calif, fill depth 120 ft,
(Los Angeles 2 million scf/D
Basin-coastal) 2500 cfm
Azusa, Calif.
She!don-Arleta
Landfill
Sun Valley,
Calif.
North Valley
(Sunshine) Land-
fill
Los Angeles,
Calif.
11 wells, average
fill depth 80 ft,
3.5 million scf/D
2400 cfm (designed
for max. 3500 cfm)
14 wells, average
fill depth 130 ft,
3 million scf/D
2000 cfm
Not available,
average fill depth
175 ft,
Not available
Triethylene Glycol
water removal and
Molecular Sieve car-
bon dioxide removal
to produce 1000 BTU/
scf gas
Triethylene Glycol
water removal pro-
viding 450 BTU/scf
± 10 percent gas
Water vapor removal to
provide 450 BTU/scf gas
Triethylene Glycol
water removal and
Molecular Sieve car-
bon dioxide removal
to product 1000 BTU/
scf gas
In operation since summer
of 1975
Gas purchased by So. Calif.
Gas Co. introduced into
local transmission system
90 day shakedown completed
August 1977, Commercial
operations to begin Jan.,
1978
Gas purchased by nearby
chemical plant; potential
for added industrial users
Recovery tests completed,
collection and 1.5 mile
pipeline under construction
Gas to be used by LA DWP
Valley Steam Plant as sup-
plementary fuel
Gas production survey com-
pleted; design reported to
Be in progress; construc-
tion pending
Reserve Synthe-
tic Fuels Inc.,
Los Angeles
County Sanitation
Districts (LACSD),
So. Calif. Gas
Co.
Azusa Land
Reclamation Co.
Southwestern
Portland Cement
parent Co.
financed
L. A. Dept. Wat
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TABLE 31. continued
ro
en
Project Name
62nd Street
Landfill
Scholl Canyon
Landfill
BKK Landfill
Ascon Landfill
City of Industry
Landfill
Pasqualletti
Landfill
Puente Hills
Landfill
Location
Denver, Col.
Glendale,
Calif.
West Covina,
Calif.
Wilmington,
Calif.
Industry,
Calif.
Phoenix,
Ariz.'
Whittier,
Calif.
Recovery System
and Gas Rate
15 wells, average
fill depth 25 ft,
3 million scf/D
2000 cfm
8 wells, average
fill depth 100 ft,
1.7 million scf/D
1200 cfm
Not available
average fill depth
200 ft, 4000 cfm
estimated
Not available
average fill depth
65 ft, 800 cfm
estimated
Not available
average fill oepth
50 ft, 400 cfm
estimated
Not available
average fill depth
35 ft, 1000 cfm
estimated
Not available
average fill depth
100 ft, 1500-3000
cfm estimated
Processing System
Not available
Not available
Ammonia synthesis
planned
Probably water
removal
Not available
No processing
planned
Probably none but
presently uncertain
Status and Utilization
Design status uncertain
project apparently pending
Gas to be sold to adjacent
asphalt plant
Analysis and survey com-
pleted; Design status not
available; generate 3000
kW peaking power 8 hours
per day using gas
Gas production survey com-
pleted; feasibility study
completed; project pending
Planning in progress; gas
survey completed; project
pending; Gas to be sold to
nearby industry
Planning and gas survey
underway; Gas to be used by
nearby golf club for club
house space heating and hot
water
Gas survey completed and
planning reported to be in
progress, implementation
depends on sales contract to
Phoenix Tallow Works
In planning stage
Sponsors/Owners
Property Improve-
ment Co.
City of Glen-
dale, Calif.
BKK Landfills
Inc, BKK Corp.
Watson Indus-
trial Properties
City of Industry
Reserve Synthe-
tic Fuels
LACSD
(continued)
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TABLE 31. continued
ro
01
Project Name
CID Landfill
Lauer No. 1
Landfill
Mountain Gate
Landfill
Holtsville
Landfill
Location
Calumet, 111.
Menonenee
Falls, Wis.
Los Angeles,
Calif.
Brookhaven,
L.I., N.Y.
Recovery System
and fia<; Rate Processing System
Average depth 120 Not available
ft.
Average depth 40 ft. Not available
Average depth 100 Not available
ft.
Average depth 40-100 Not available
ft.
Status and Utilization
Gas survey completed;
project pending
Gas survey completed;
project pending
Has migration system
installed; gas survey
compl eted
.Survey and gas migration
control system contract let;
recovery system will follow
if feasible
Sponsors/Owners
Reserve Synthe-
tic Fuels
Reserve Synthe-
tic Fuels
City of Los
Angeles,
LACSD
Brookhaven, L.I.
N.Y, Reserve
Landfill Dev. Co.
m = 0.3048 x ft
std cu m/min = 19.652 x MM scf/day
cu m/min = 0.02832 x cfm
kO/cu m =37.32 x BTU/scf
-------
Accordingly, Table 32 lists three types of demonstration projects
suggested for consideration.
1- Landfill Gas Recovery and Processing (Raw and Upgraded Gas)
The collection, analysis and reduction of performance, operation
and cost/economic data from ongoing gas recovery and processing
projects is suggested. At least one facility that is delivering
dehydrated gas and another that is upgrading the gas to near nat-
ural gas standards, should be included. Collection and analysis
of data from multiple installations of different capacities would
be highly desired.
2- Landfill Gas Recovery and Utilization (Steam and Electricity
A similar assessment of a steam generation/steam turbine-electrical
generator operation or separate evaluations of steam generation
and some form of electricity generation is recommended. The cost
of these demonstration projects need not exceed from one to perhaps
three million dollars capital investment.
3. Environmental Effects of Landfill Gas Recovery, Processing, and
Utilization ~ ~
The third demonstration project suggested is to evaluate the
environmental impacts, pollution control techniques and potential
mitigation measures applicable to landfill gas recovery, processing
and utilization. It appears that because of the clean burning
properties of landfill gas (methane) and the harmless effects of
carbon dioxide and water vapor when emptied into the atmosphere,
such projects will have negligible adverse impacts. Nonetheless,
primary and secondary effects must be determined and evaluated
The approach suggested is to monitor the available demonstration
and R&D projects.
127
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ro
oo
Pro.lect title
TABLE 32. SUGGESTED LANDFILL _GAS DEMONSTRATION PROJECTS
Project objectives
Estimated duration
(months)
Demonstration of Landfill
Gas Recovery and Pro-
cessing Systems (Raw and
Upgraded Gas Utiliza-
tions)
Full-scale proof-of-process
- gas recovery and processing
technical and economic
feasibility
Demonstration of Landfill Full-scale proof-of-process
Gas Recovery and Utiliza- - gas recovery/processing
tion Systems (Steam and and utilizations, technical
Electricity) and economic feasibility
Evaluation of Environ-
mental Effects of Land-
fill Gas Recovery/Pro-
cessing/Utilization
Independently evaluate
pollutants, pollution con-
trol and environmental
impacts of demonstration
projects
Estimated work content (person-months)
Analysis/design/reports Laboratory work Field work
18 to 24 6 to 12
(Data review, analysis
and reduction only)
18 to 24 36 to,48
12 to 18 12 to 18
2 to 4
2 to 4
4 to 6
4 to 8
12 to 24
12 to 18
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REFERENCES
1. Blanchet, M. J and Staff of the Pacific Gas and Electric Company.
Treatment and Utilization of Landfill Gas, Mountain View Project
Feasibility Study. EPA/ 530/SW-583, 1977.
2. IsdflbUM. Ll . A. KPrnVOPU nt lanH-F-ill P,^ 34. Mnimta-in yip
3. Bowerman F. R., N. K Rohatgi, K. Y. Chen, and R. A. Lockwood. A Case
undfin
*****
5. Genetelle, E J. and J. Cirello, Editors. Gas and Leachate from Land
lQ7fi Format'0"' Collection and Treatment. EPA 600/9-76-004, Mar.
'
of Gas and Leachate in Landfills.
7. Bryant, M P. The Microbiology of Anaerobic Degradation and Methanoge-
nesis with Special Reference to Sewage, Microbial Energy Conversion In
Proceedings of Seminar at Gottengen, West Germany, Oct 4-8, 1976
Erich Goltze KG, D-300 Gottingen, Stresemann Str., 1976. p 107
8. Farquhar, G J., and F. A. Rovers. Gas Production During Refuse Decom-
position, Water, Air and Soil Pollution, 2. 1973. pp 483-495.
9' I'ulosp'nb^ion' M-nQaK-'1a?d K' °hwakl<- Methane Formation and Cel-
lulose Digestion, Microbial Energy Conversion. In: Proceedings of Sem-
DUnn rn?trn9en'^est Germany' Oct' 4-8' 1976' En'ch Golt^e KG,
D-3400 Gottingen, Stresemann Str., 1976. p. 97.
10. Rarnaswarny J N Nut^tional Effects on Acid and Gas Production in
Sanitary Landfills. Ph.D. Dissertation, University or West Virginia
Morgantown, West Virginia, 1970. v.rymid,.
' |S3?l?a' °Ph°n °n- AC1> GaS' dnd Ml'crob1al Dynamics in Sanitary
129
-------
12. Kotze, J. P., P. G. Thiel, and W. H. 0. Hattingh. Anaerobic Diges-
tion II, the Characterization and Control of Anaerobic Digestion,
Water Research, Vol. 9, Pergaman Press, Great Britain, 1969.
13. Boyle, W. D. Energy Recovery from Sanitary Landfills - A Review,
Microbial Energy Conversion. In: Proceedings of Seminar at Gottingen,
West Germany, Oct. 4-8, 1976. Erich Goltze KG, D3400 Gottingen,
Stresemann Str. p. 119.
14. Bell, J. M. Development of a Method for Sampling and Analyzing Re-
fuse. Ph.D. Dissertation, Purdue University, Lafayette, Indiana
(1963). Abstracted from R. C. Corey, Principles and Practices on
Incineration, Wiley Interscience, New York, 1969.
15. McCarty, P. L. Anaerobic Waste Treatment Fundamentals, Parts 1, 2
and 3. Public Works, Sept., Oct. and Nov. 1964.
16. Golueke, C. J. Comprehensive Studies of Solid Waste Management; Third
Annual Report. EPA SW-lOrg, 1971.
17 Anderson, D. R. and J. P. Callinan. Gas Generation and Movement in
Landfills, Industrial Solid Waste Management. In: Proceedings of
National Industrial Solid Wastes Management Conference, University of
Houston, Houston, Texas, 1970. p. 311.
18. Pacey, J. Methane Gas in Landfills: Liability or Asset? In: Pro-
ceedings of Congress on Waste Management Technology and Resource and
Energy Recovery, EPA SW-8p, 1976. p 168.
19. Klein, S. A. Anaerobic Digestion of Solid Wastes, Compost Science,
Jan./Feb. 1972. p. 6.
20. Hitte, S. J. Anaerobic Digestion of Solid Waste and Sewage Sludge
into Methane, Compost Science, Jan./Feb. 1976. p. 26.
21 Pfeffer, J. T. Reclamation of Energy from Organic Waste. EPA 679/2-
74-016 (NTIS Report PB-231 176), 1974.
22 Schwegler, R. E. Energy Recovery at the Landfill. Presented at llth
Annual Seminar and Equipment Show, Governmental Refuse Collection and
Disposal Assoc., Santa Cruz, California, Nov. 7-9, 1973.
23. Hekimian, K. K., W. J. Lockman, and J. H. Hirt. Methane Gas Recovery
from Sanitary Landfills, Waste Age, Dec. 1976.
24 Alpern, R. Decomposition Rates of Garbage in Existing Los Angeles
Landfills. Unpublished M.S. Thesis, California State University at
Long Beach, adapted from Reference 29, 1973.
25 City of Los Angeles, Bureau of Sanitation, Research and Planning
Division. Estimation of the Quantity and Quality of Landfill Gas
from the Sheldon-Areleta Sanitary Landfill. Jan. 2, 1976.
130
-------
26. VTN Consolidated, Inc. Environmental Impact Reports on NRG NUFuel
Company's Landfill Gas Processing System, Prepared for the City of
Rolling Hills Estates, California, Jan. 1975.
27. Merz, R. C. Investigation to Determine the Quantity and Quality of
bases Produced during Refuse Decomposition, Final Report to State
Water Quality Control Board, Agreement No. 12-13. USCEC Report 89-10,
University of Southern California, Los Angeles, Adapted from Reference
oo 9 i yoH
28. Merz, R. C. and R. Stone. Quantitative Study of Gas Produced by
Decomposing Refuse. Public Works, Nov. 1968. p. 86.
29. Rovers, R. A. and G. J. Farguhar. Infiltration and Landfill Behavior.
Journal Environmental Engineering Division, Am. Soc. Civil Enqrs.
99, EE5, Oct. 1973. p. 671.
30. Streng, D. R. The Effects of Industrial Sludges on Landfill Leachates
and Gas, Management of Gas and Leachate in Landfills. EPA-600/9-77-
026, Sept. 1977. p. 41.
31. Chi an, E. S. K. , E. Hammerburg, and F. B. DeWalle. Effect of Mois-
ture Regimes and Other Factors on Municipal Solid Waste Stabilization,
Management of Gas and Leachate in Landfills. EPA-600/9-77-026, Sept.
i y / / m p / o
32. Beluche, R. Degradation of Solid Substrate in a Sanitary Landfill.
Ph.D. Dissertation, University of Southern California, Los Angeles,
33. Merz, R. C., and R. Stone. Gas Production in a Sanitary Landfill.
Public Works, 95, 2, 1964. p. 84.
34. McCarty, P. L. The Methane Fermentation, Principles and Applications
in Aquatic Microbiology, John Wiley and Sons, Inc., New York, 1963.
35. Carlson, EL. A Study of Landfill Gas Migration in Madison, Wiscon-
sin. Unpublished M.S. Report, University of Wisconsin, Madison, 1977.
36. Disposal Branch, SHWRL, NERC, EPA, Cincinnati, Ohio. Summary Report:
faas and Leachate from Land Disposal of Municipal Solid Waste. 1974.
37. SCS Engineers. Environmental Inpact Report on 'Industry Hills Civic-
Recreation-Conservation Project1, Interim Report. Prepared for the
Industry Urban-Development Agency, SCS Engineers, Long Beach, Cali-
fornia, Apr. 16, 1975.
38. Bishop, W. D., et al . Water Pollution Hazards from Refuse Produced
Carbon Dioxide, Advanced Water Pollution Research, Ed. Jaag, 0. and
H. Liebman, Water Pollution Control Federation, Wash. D.C. 1967
131
-------
39. Engineering-Science, Inc. Final Report, In-Site Investigation of
Movements of Gases Produced from Decomposing Refuse, State Water
Quality Control Board, Publication No. 35, State of California, 1967.
40. Emcon Associates and Jacobs Engineering Co. A Feasibility Study of
Recovery of Methane from Parcel 1 of the Scholl Canyon Sanitary Land-
fill. Prepared for the City of Glendale, California, Oct. 1976.
41. Dair, F. R. Methane Gas Generation from Landfills. Presented at
American Public Works Association Conference, Las Vegas, Nevada,
Sept. 27, 1976.
42. Ralph M. Parsons Company. Engineering and Economic Analysis of Waste-
to-Energy Systems. U. S. Environmental Protection Agency, Cincinnati,
Ohio, June 1977.
43. Brown, J. W., J. T. Pfeffer and J. C. Liebman, Department of Civil
Engineering, Illinois University, Urbana, Illinois. Biological Con-
version of Organic Refuse to Methane, Final Report. Energy Research
and Development Agency, COO/2917-3, Volumes 1 and 2, Nov. 1976.
44. Dynatech R/D Company. Fuel Gas Production from Solid Waste, Semi-
Annual Progress Report. Number 1207, National Science Foundation
July 31, 1974.
45. Dynatech R/D Company. Evaluation of Systems for Purification of Fuel
Gas from Anaerobic Digestion Engineering Report. Energy Research and
Development Agency, Number 1628, June 17, 1977.
46. Bechtel Corporation. Edison Coordinated Joint Regional Solid Waste
Energy Recovery Project, Feasibility Investigation. Southern Califor-
nia Edison Company, Apr. 1977.
47. Cost Control Department, Daniel, Mann, Johnson & Mendenhall. Study
of Building Cost Increases from 1947 through 1976 Inclusive. Jan.
20, 1977.
48. U. S. Environmental Protection Agency. Fourth Report to Congress:
Resource Recovery and Waste Reduction. SW-600, 1977.
49. Pfeffer, J. T., J. C. Liebman, Department of Civil Engineering,
University of Illinois at Urbana-Champaign, Illinois. Biological
Conversion of Organic Refuse of Methane, Semi-Annual Progress Report.
National Science Foundation, Jan. 1975.
50. Pfeffer, J. T., J. C. Liebman, Department of Civil Engineering,
University of Illinois at Urbana-Champaign, Illinois. Biological
Conversion of Organic Refuse to Methane, Annual Progress Report.
National Science Foundation, July, 1974.
132
-------
51. DeRenzo, D. J. Energy from Bio-Conversion of Waste Materials. Ed.
Noyes Data Corporation, 1977.
52. Congeneration (a brochure). Garrett Corporation, SPA 4803-1A, Oct.
I -/ / /
53. Ashave, E., et al, Dynatech R/D Company. Evaluation of Systems for
Purification of Fuel Gas from Anaerobic Digestion. U. S. Energy
Research and Development Administration, (00-2991-19) June 1977.
54. Consumat Systems Inc. Brochure and Cost Data, 1975.
55. Sanitary Landfill Design and Operation. EPA/SW-654S, 1972.
56. Liners for Land Disposal Sites, An Assessment. EPA/530/SW-137, Mar.
I -/ / D
57. Successful Sanitary Landfill Siting. EPA/SW-617, 1977.
58. Sanitary Landfill ing, Report on the Joint Conference. Sponsored by
the National Solid Waste Management Association and U. S. EPA,
EPA/SW-5p, 1973.
59. Los Angeles County and Engineering Science Inc. Development of Con-
struction and Use Criteria for Sanitary Landfills, An Interim Report.
U. S. Dept. Health, Education and Welfare, 1969.
60. American Society of Civil Engineers. Sanitary Landfill, ASCE Manual
on Engineering Practice. Prepared by the ASCE Solid Waste Management
Committee of the Environmental Energy Division, 1976.
61. Reinhardt, J. J. and R. K. Ham. Solid Waste Milling and Disposal on
Land Without Cover, Volume I, Summary and Major Findings. EPA NTIS
PB 234 930, 1974.
133
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TECHNICAL REPORT DATA
(Please read Instructidns on the reverse before completing)
REPORT NO.
EPA-600/2-79-001
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
RECOVERY, PROCESSING, AND UTILIZATION OF GAS
FROM SANITARY LANDFILLS
. REPORT DATE
February 1979 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
Robert K. Ham
Kenneth K. Hekimian
Stanley L. Katten
Wilbur J. Lockman
Ronald J. Lofy
Donald E.
McFaddin
Edward J. Da 1 e.y
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
Lockman & Associates
249 East Pomona Boulevard
Monterey Park, California 91754
10. PROGRAM ELEMENT NO.
1DC618
11. CONTRACT/GRANT NO.
EPA No. 68-03-2536
2. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research LaboratoryCin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 3/77 - 9/78
14. SPONSORING AGENCY CODE
EPA/600/14
5. SUPPLEMENTARY NOTES
Project Officer - Stephen C. James 513/684-7881
6. ABSTRACT
The report is organized into seven sections. Following the introduction and
conclusions and recommendations, are sections describing: the three-component gas
generation phenomenon; analysis and comparison of alternative gas utilizations in-
cluding the processes necessary to prepare the gas for use; an evaluation of various
landfill design approaches and operations techniques that show promise for enhancing
gas generation, recovery efficiency and quality; recommendations for research, devel-
opment and demonstration projects deemed necessary to develop an adequate data base
to proceed with more in depth engineering evaluations of the various options.
Overall, it is shown that landfill gas recovery,
technically feasible and can be economically viable.
processing and utilization is
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Gas production, gas purification, engi-
neering costs, design criteria, waste
disposal, gas wells, optimization, chem-
ical engineering, unit operations
landfill gas, utilization
alternatives, landfill
gas generation, landfill
gas composition, landfill
operation
50C
85E
94C
94E
97 K
970
99B
68C
18. DISTRIBUTION STATEMENT
Public Distribution
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
146
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
134
4 U.S. GOVERNMENT PRINTING OFFICE: 1979-657-060/1603
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