Energy recovery from sanitary landfills - a review


Boyle, W.C.

Proceedings of a Seminar Sponsored by the UN Institute for Training and Research (UNITAR) and the Ministry for Research and Technology of the Federal Republic of Germany Held in Göttingen, October 1976: 119-138

1977


The state-of-the-art of in-situ methane production and extraction from municipal solid waste landfills is reviewed. Characteristics of municipal solid waste and the landfill environment are discussed in light of their influence on methane gas generation. Gas extraction and cleaning methods currently being used are presented and options available for gas utilization are cited. Current experiences with large-scale extraction from California landfills are cited. A preliminary evaluation of this potential source of energy is given in light of net energy yields.

ENERGY
RECOVERY
FROM
SANITARY
LANDFILLS
-
A
REVIEW
W.
C.
Boyle
The
University
of
Wisconsin,
Department
of
Civil
&
En/ironmental
Engineering,
Madison,
Wisconsin,
U.S.A.
Abstract:
The
state-of-the-art
of
in
-situ
methane
production
and
extraction
from
municipal
solid
waste
landfills
is
reviewed.
Characteristics
of
municipal
solid
waste
and
the
landfill
environment
are
discussed
in
light
of
their
influence
on
methane
gas
generation.
Gas
extraction
and
cleaning
methods
currently
being
used
are
presented
and
options
available
for
gas
utilization
are
cited.
Current
experiences
with
large-scale
extraction
from
California
landfills
are
cited.
A
preliminary
evaluation
of
this
potential
source
of
energy
is
given
in
light
of
net
energy
yields.
119
With
the
greater
incentives
placed
on
society
today
to
seek
alternate
sources
of
energy,
municipal
solid
wastes
are
being
considered
as
a
potentially
useful
fuel
resource.
On
the
basis
of
weight,
more
than
75
percent
of
the
solid
waste
generated
in
the
U.S.A.
is
combustible.
The
USEPA
estimates
that
in
1980
over
160
million
wet
tons
of
refuse
will
be
generated
in
the
U.S.A.
(based
on
an
estimated
per
capita
generation
of
3.91
wet
pounds/day,
and
a
population
of
approximately
226
million)
(Lowe
1974).
Not
all
solid
waste
generated
would
be
available
for
energy
recovery,
however,
since
typical
energy
recovery
systems
depend
upon
economics
of
scale
and
require
large
quantities
of
waste
to
be
delivered
for
processing
at
one
site.
Based
on
more
densely
populated
areas
in
the
U.S.A.
(Standard
Metropolitan
Statistical
Areas),
the
potential
annual
generation
rate
for
1980
would
be
121
million
wet
tons
of
refuse
(based
on
a
per
capita
generation
in
populated
areas
of
4.33
lb/day,
and
152.6
million
people).
Using
a
calorific
value
for
raw,
wet
refuse
of
approximately
4500
BTU/lb,
this
would
amount
to
1,085
x
10
12
BTU
(273
x
10
12
K
cal)
of
potential
energy
per
year
in
1980
or
approximately
1%
of
the
estimated
total
U.S.
energy
demand
for
that
year.
Of
course,
the
actual
amount
of
energy
recovered
from
this
source
will
depend
upon
efficiencies
of
the
processes
utilized.
Net
energy
yields,
expressed
as
a
per-
centage
of
input
refuse
energy
content,
range
from
approximately
10%
for
methane
recovery
from
some
landfills,
through
30-40%
for
pyrolysis,
to
as
high
as
60%
for
heat
recovery
incineration.
Historically,
thermal
reduction
of
solid
wastes
has
referred
to
the
incinera-
tion
process
carried
out
largely
in
refractory
-lined
chambers.
More
recently,
how-
ever,
new
ways
of
treating
and
handling
refuse
to
convert
it
to
useful
forms
of
energy
have
been
developed.
The
energy
products
most
often
suggested
for
solid
wastes
include
steam,
solid
fuel,
liquid
fuel,
gaseous
fuel,
and
electricity
(Colonna
and
McLaren,
1974).
Several
processes
are
being
considered
for
the
conver-
sion
of
solid
wastes
to
fuel
gas,
including
pyrolysis,
hydrogasification,
and
anaer-
obic
digestion.
The
production
of
methane
from
anaerobic
digestion
of
solid
waste
may
take
place
in
essentially
an
uncontrolled
environment
within
a
disposal
site
or
120
Table
I
Composition
and
Analysis
of
an
Average
Municipal
Refuse
(Bell,
1963)
Percent
of
all
Refuse
by
Weight
Moisture
(percent
by
weight)
Analysis
(percent
dry
weight)
Calorific
Value
(Btu/lb)
Volatile
Matter
Carbon
Hydrngen
Oxygen
Nitrogen
Sulfur
Noncom-
bustibles
a
Rubbish
64%
Paper
42.0
10.2
84.6
43.4
5.8
44.3
0.3
0.20
6.0
7572
Wood
2.4
20.0
84.9
50.5
6.0
42.4
0.2
0.05
1.0
8613
Grass
4.0
65.0
--
43.3
6.0
41.7
2.2
0.05
6.8
7693
Brush
1.5
40.0
--
42.5
5.9
41.2
2.0
0.05
8.3
7900
Greens
1.5
62.0
70.3
40.3
5.6
39.0
2.0
0.05
13.0
7077
Leaves
5.0
50.0
--
40.5
6.0
45.1
0.2
0.05
8.2
7096
Leather
0.3
10.0
76.2
60.0
8.0
11.5
10.0
0.40
10.1
8850
Rubber
0.6
1.2
85.0
66.9
10.4
--
--
2.0
10.0
11330
Plastics
0.7
2.0
--
48.1
7.2
22.6
-- --
10.2
14368
Oils,
paints
0.8
0.0
--
55.0
9.7
5.2
2.0
--
16.3
13400
Linoleum
0.1
2.1
65.8
5.3
18.7
0.1
0.40
27.4
8310
Rags
0.6
10.0
93.6
34.7
6.6
31.2
4.6
0.13
2.5
7652
Street
20.6
Sweepings
3.0
20.0
67.4
16.6
4.8
35.2
0.1
0.20
25.0
6000
Dirt
1.0
3.2
21.2
2.6
4.0
0.5
0.01
72.3
3790
Unclassified
0.5
4.0
--
2.5
18.4
0.05 0.05
62.5
3000
Food
Wastes,
12%
Garbage
10.0
72.0
53.3
45.0
6.4
28.8
3.3
0.52
16.0
8484
Fats
2.0
0.0
76.7
12.1
11.2
0
0 0
16700
Noncombustibles,
24%
Metals
8.0
3.0
0.5
0.8
0.04
0.2
99.0
124
Glass
and
Ceramics
6.0
2.0
0.4
0.6
0.03
0.1
99.3
65
Ashes
10.0
10.0
3.0
23.0
0.5
0.8
0.5
70.2
4172
Com
dafuq-,
a-
Received
All
refuse
100
20.7
28.0
3.5
22.4
0.33
0.16
24.9
6203
a.
Ash,
metal,
glass,
and
ceramics
in
carefully
controlled
reactor
systems.
It
is
the
intent
of
this
paper
to
review
the
current
state-of-the-art
of
in
-situ
methane
production
and
extraction
from
actively
decomposing
municipal
sanitary
landfills.
Municipal
Solid
Waste
Characterization
The
substrate
available
for
methanogenesis
in
sanitary
landfills
is
solid
waste
generated
by
the
municipality
and
includes
a
variety
of
materials
and
generat-
ing
sources.
The
quantity
and
quality
of
municipal
solid
wastes
is
highly
variable
depending
upon
geographical
location,
standard
of
living
of
the
population,
and
season
of
the
year.
Since
composition
studies
are
very
expensive
to
conduct,
cur-
rent
analyses
of
solid
wastes
are
not
available
readily,
but
the
thorough
analyses
performed
by
Bell
(1963)
are
widely
quoted
even
today
and
appear
in
Table
I.
A
more
recent
tabulation
of
relative
amounts
of
solid
waste
generated
from
U.S.
resi-
dential
and
commercial
sources
as
provided
by
the
USEPA
(Smith,
1975)
is
presented
in
Table
II.
Finally,
a
relative
comparison
in
solid
waste
composition
between
three
developed
countries
is
depicted
in
Table
III
(Sumner,
1967).
Table
II
U.
S.
Residential
and
Commercial
Solid
Waste
(Smith,
1975)
Kinds
of
Materials
Material
totals
on
an
"as
disposed"
basis
10
6
tons/yr
Paper
47.3
37.8
Glass
12.5
10.0
Metals
12.6
10.1
Ferrous
11.3
9.0
Aluminum
0.9
0.7
Non-ferrous
0.4
0.3
Plastics
4.7
3.8
Rubber
&
Leather
3.4
2.7
Textiles
2.0
1.6
Wood
4.6
3.7
Food
Wastes
17.7
14.2
Yard
Wastes
18.2
14.6
Misc.
Inorganics
1.9
1.5
125.0
100.0
The
difficulty
in
drawing
comparisons
between
various
solid
waste
composition
studies
lies
in
the
way
in
which
materials
are
classified
and
the
presence
of
mois-
ture.
All
three
tables
are
based
on
wet
weight
measurements,
but
moisture
levels
in
the
EPA
tabulation
and
the
International
Survey
were
not
given.
Furthermore,
ash,
which
accounts
for
as
much
as
10%
of
the
refuse
weight,
was
omitted
in
the
EPA
tabu
-
122
lation.
Addition
of
solid
wastes
from
industrial
sources,
street
cleaning,
demoli-
tion
debris,
animal
wastes,
and
sewage
sludge
further
complicate
characterization.
Table
III
Comparison
of
Relative
Compositions
of
Solid
Wastes
From
Three
Countries
(Sumner,
1967)
Kinds
of
Materials
Material
-
Percent
by
Weight
U.S.A.
France
Sweden
Paper
42
29.6
55.0
Organic
Matter
22.5
24.0
12.0
Ash
10.0
24.3
0.0
Metals
8.0
4.2
6.0
Glass
6.0
3.9
15.0
Miscellaneous
11.5
14.0
12.0
100.0
100.0
100.0
These
tables
show
that
the
major
ingredient
in
municipal
solid
waste
is
paper
and
paper
products,
although
this
component
is
currently
being
reduced
in
solid
wastes
as
the
incentives
for
paper
recycle
improve.
Based
upon
"typical"
municipal
solid
waste
analyses,
it
is
apparent,
however,
that
about
75%
of
the
municipal
solid
waste
generated
in
the
U.S.
is
combustible
and
that
up
to
approximately
50%
of
it
is
biodegradable
(Bell,
1963).
In
contrast,
the
International
Survey
(Sumner,
1967)
indicated
that
European
refuse
is
20-40%
more
dense
than
that
of
the
U.S.,
has
30-
60%
less
salvables,
30%
less
combustibles,
65%
less
putrescibles,
and
15-25%
lower
calorific
value.
The
Sanitary
Landfill
The
sanitary
landfill
may
be
defined
as
a
process
of
solid
waste
disposal
on
land
without
creating
nuisances
to
public
health
or
safety
by
confining
the
solid
waste
to
the
smallest
practical
area,
to
reduce
it
to
the
smallest
practical
volume,
and
to
cover
it
with
layers
of
earth
at
the
conclusion
of
each
day's
operation.
Essentially,
solid
wastes
may
be
placed
in
properly
sited
sloping
land,
ravines,
canyons,
marshes,
quarries,
or
man-made
depressions
and
then
compacted
to
about
1000
lbs/cu
yd
with
appropriate
machinery
prior
to
being
covered
with
approximately
6
inches
of
soil
cover.
Landfilling
on
flat
or
gently
sloping
land
is
also
practiced
whereby
excavation
of
trenches
is
provided
followed
by
subsequent
filling,
compact-
ing,
and
covering.
Sanitary
landfills
vary
in
depth
from
several
hundred
feet
in
deep
canyons
to
8-10
feet
in
flat
land
areas.
Depending
upon
soil
conditions
and
geological
characteristics,
landfills
may
be
lined
with
impervious
material
prior
to
123
disposal
of
refuse
to
avoid
percolation
of
landfill
leachate
into
nearby
ground
or
surface
water
sources.
In
addition,
landfill
cover
is
designed
normally
to
minimize
erosion
and
encourage
proper
drainage.
Many
landfills
are
provided
also
with
appro-
priate
impervious
barriers
or
venting
trenches
to
protect
against
lateral
diffusion
of
methane
gas.
In
many
instances
it
is
economically
advantageous
to
pretreat
solid
wastes
prior
to
deposition
in
landfills.
Milling,
shredding,
or
pulverizing
refuse
pro-
vides
for
significant
volume
reduction,
reduces
the
need
for
less
cover
material,
and
provides
for
greater
flexibility
in
further
solid
waste
processing
including
magnetic
separation
and
air
classification.
Baling
solid
wastes
is
also
practiced
to
some
extent,
providing
more
economical
transportation
of
solid
wastes
to
disposal
sites
and
reducing
water
volume.
It
is
apparent
from
this
abbreviated
description
that
the
practice
of
sanitary
landfilling
is
highly
variable,
being
designed
to
meet
the
specific
characteristics
of
the
site
and
solid
waste.
Therefore,
the
environment
under
which
solid
wastes
decompose
is
highly
variable
from
site
to
site
and
is
most
difficult
to
assess
with-
out
preliminary
testing.
Gas
Generation
in
Sanitary
Landfills
Gas
Volume
and
Composition
The
biological
stabilization
of
solid
wastes
in
a
landfill
will
normally
under-
go
a
sequence
of
changes
as
the
decomposition
proceeds.
A
typical
pattern
of
gas
production
may
be
depicted
as
in
Figure
1
and
is
normally
divided
in
four
phases.
The
aerobic
phase
is
normally
relatively
short
in
landfills
since
quantities
of
oxygen
are
limited.
Carbon
dioxide
is
produced
in
approximately
a
molar
equivalent
to
the
oxygen
consumed
and
little
nitrogen
is
displaced.
In
the
anaerobic,
non-
methanogenic
phase,
a
CO
2
"bloom"
often
occurs
as
organic
acid
production
proceeds.
These
blooms
which
may
produce
as
much
as
90%
CO
2
have
been
reported
to
occur
after
11
days
(70%
CO
2
)
and
23
days
(50%
CO
2
)
by
the
California
Water
Quality
Board
(1967)
and
after
40
days
(90%
CO
2
)
by
Beluche
(1968).
Also,
hydrogen
production
increases
and
nitrogen
displacement
normally
increases
dramatically.
In
phase
three,
methano-
genic
activity
is
initiated
and
methane
concentrations
increase
as
CO
2
and
hydrogen
124
levels
decrease.
This
unsteady
-state
phase
has
been
found
to
occur
as
early
as
180
days
after
landfilling
(Ramaswamy,
1970),
250
days
(Rovers
&
Farquhar,
1973),
or
as
late
as
500
days
(Beluche,
1968).
The
steady-state
production
of
methane
occurs
considerably
later,
if
at
all,
in
landfill
systems.
FIGURE
I
TYPICAL
SEQUENCE
OF
GAS
PRODUCTION
IN
SANITARY
LANDFILLS
100
GAS
COMPOSITION
-
%
BY
VOLUME
50
I
0
2
II
0
III
IV
CH
4
TIME
OF
PLACEMENT
The
total
gas
generated
in
a
landfill
depends
upon
the
quality
and
quantity
of
materials
placed
in
the
fill
volume.
Estimates
of
methane
gas
production
require
characterization
of
the
solid
waste.
The
maximum
gas
production
may
then
be
calcu-
lated
from
stoichiometric
considerations
using
the
reaction,
b
c
3d
e
C
a
H
b
O
c
N
d
S
e
+
(a
-
-
4
-
-
-
2
-
+
I
T+
-
2
-
)
H
2
O
(a
+
b
-
c
-
3d
-
e
)
CH
4
+
(a
-
b
+
c
+
3d
+
e
)
CO
2
+
dNH
3
+
ell
2
S.
(1)
2
8
4
8
4
2
8
4
8
4
Observation
of
equation
(1)
indicates
that
1
mole
of
organic
carbon
will
theo-
retically
yield
1
mole
of
CH
4
and
CO
2
gas
or
that
one
pound
will
produce
32.5
SCF
of
CH
4
and
CO
2
at
standard
conditions.
The
relative
quantity
of
CH
4
and
CO
2
would
be
dependent
upon
the
organic
composition;
for
example,
paper
will
produce
theoret-
ically
a
molar
ratio
CO
2
:CH
4
of
about
1,
whereas,
the
garbage
fraction
will
yield
125
a
CO
2
:CH
4
ratio
of
approximately
0.5.
Based
on
a
dry
carbon
content
of
28%
(Table
I),
9.1
SCF
of
gas
would
be
produced
per
pound
of
dry
solid
waste
or
7.2
SCF/lb
based
on
a
wet
weight
(20.7%
moisture).
Refinements
of
this
calculation
may
be
made
by
employing
bio-
degradability
coefficients
for
various
components
within
the
waste.
A
more
empir-
ical
approach
has
been
to
estimate
production
on
the
basis
of
total
organic
content
or
volatile
solids
concentrations.
For
example,
Anderson
and
Callinan
(1970)
computed
that
the
decomposition
of
each
pound
of
the
solid
wastes
appearing
in
Table
I
is
theoretically
capable
of
producing
2.7
SCF
of
CO
2
and
3.9
SCF
of
CH
4
,
or
6.6
SCF
per
dry
pound
of
waste.
These
calculations
were
based
on
a
volatile
solids
content
of
75%.
Pacey
(1976)
reported
that
weighting
of
each
volatile
component
in
the
waste
in
accordance
with
its
biodegradability
would
result
in
a
production
of
approximately
1
SCF
of
CH
4
per
pound
of
waste.
By
fractionating
organic
solid
wastes
into
Kraft
paper
(40%),
newsprint
(33%),
and
other
organics
(27%),
Golueke
(1971)
calculated
a
total
gas
production
of
8.8
SCF/lb
dry
volatile
matter.
Actual
total
gas
production
volumes
in
landfills
will
be
substantially
lower
than
those
calculated
on
theoretical
bases.
Significant
amounts
of
the
CO
2
generat-
ed
will
likely
be
dissolved
in
the
water
phase
in
solid
wastes.
Generation
of
gas
in
landfills
is
also
dependent
upon
the
landfill
age;
landfill
constructional
character-
istics;
landfill
operations;
and
the
landfill
environment,
including
moisture
content,
temperature,
pH,
oxidation-reduction
potential,
nutrient
availability,
infiltration,
and
presence
of
toxic
materials.
Moisture
levels
in
landfills
are
normally
low,
ranging
from
15-40%
(wet
weight).
Numerous
investigators
(Ramaswamy,
1970;
Songanuga,
1969;
California,
1967;
Merz
and
Stone,
1968)
have
demonstrated
that
gas
production
increases
as
moisture
in-
creases
and
maximum
production
is
believed
to
occur
in
the
range
of
60
to
80%
moist-
ure
(wet
weight)
based
upon
laboratory
and
pilot
studies.
Excessive
infiltration
of
moisture
may,
however,
be
detrimental
to
methenogenesis
as
discussed
by
Fungaroli
&
Steiner,
1971;
Songonuga,
1969;
Ramaswamy,
1970;
and
Rovers
&
Farquhar,
1973.
High
freshwater
flows
resulted
in
decreased
gas
production,
pH
and
temperature
and
possibly
increased
oxidation-reduction
potentials.
126
Optimum
temperatures
for
anaerobic
sludge
digestion
have
been
reported
to
be
approximately
35
°
C
(McCarty,
1963;
Kotze,
et
al,
1969).
Landfill
temperatures
are
influenced
by
aerobic
activity
usually
reaching
a
maximum
value
anywhere
from
1
to
as
long
as
45
days
after
placement
(Quasim
and
Burchinal,
1970;
Bevan,
1967;
Rovers
&
Farquhar,
1973;
California,
1967).
Once
anaerobic,
landfill
temperatures
decrease,
being
lower
at
greater
depths,
and
are
influenced
by
ambient
air
temperatures.
For
example,
Rovers
&
Farquhar
(1973)
reported
temperature
variations
of
from
2
°
C
to
21
°
C
with
a
mean
of
10
°
C
at
a
5
ft
depth
for
Canadian
conditions.
It
is
generally
agreed
that
landfill
temperatures
are
normally
well
below
those
which
would
yield
optimum
methane
production.
Optimal
pH
values
for
anaerobic
digestion
ranges
from
6.4
to
7.4
(Kotze
et
al,
1969;
McCarty,
1963).
pH
values
found
in
landfills
may
be
influenced
by
industrial
waste
discharges,
alkalinity,
clear
water
infiltration,
and
relative
rates
of
organic
acid
production
and
methane
generation.
Values
of
pH
measured
in
actively
decompos-
ing
landfills
producing
methane
gas
are
normally
in
excess
of
pH
5.5.
The
shredding
of
solid
wastes
prior
to
landfilling
has
been
shown
to
enhance
the
rate
of
decomposition
of
organic
material
as
might
be
expected
(Lin,
1966).
Leachate
compositions
from
landfills
containing
shredded
waste
indicate
an
earlier
onset
of
anaerobiosis
and
methane
production
is
initially
much
higher
than
in
unshredded
waste
landfill
plots.
Examination
of
excavated
landfills
25
years
after
placement
has
indicated
that
the
waste
is
greatly
segregated
with
relatively
large
quantities
of
unreacted
organic
materials
and
uneven
distributions
of
moisture
(USEPA,
1976).
Shredding
provides
a
more
homogeneous
mixture
of
wastes
with
high
surface
area
and
promotes
more
effective
moisture
routing
and
retention
within
the
landfill.
Gas
compositions
found
in
existing
landfill
vary
greatly
with
landfill
age,
composition,
and
environment.
Under
steady
state
conditions
of
methanogenesis,
gas
compositions
of
methane
will
range
normally
from
50
to
70%
(Beluche,
1968;
Bevan,
1967;
Ramaswamy,
1970).
Data
collected
at
the
Sheldon
-Arleta
landfill
indicate
a
City
of
gas
composition
of
57%
CH
4
and
43%
CO
2
(Los
Angeles,
1976).
Gas
composition
at
the
Palos
Verdes
landfill
site
are
reported
to
be
53%
CH4
and
43-45%
CO2
with
traces
of
127
N
2
,
0
2
,
and
some
hydrocarbons
(USEPA,
1976).
Methane
levels
below
50%
and
presence
of
high
concentrations
of
N
2
suggest
suboptimal
performance
of
the
landfill.
Kinetics
of
Gas
Generation
One
of
the
most
critical
pieces
of
information
required
in
assessing
the
potential
of
solid
waste
landfills
for
energy
recovery
is
the
rate
of
gas
generation
and
the
expected
life
of
a
given
site.
Unfortunately,
to
date,
the
kinetics
of
landfill
gas
generation
is
poorly
documented
and
theoretical
analyses
must
draw
on
the
anaerobic
sludge
digestion
literature.
Mathematical
formulation
is
based
upon
the
concept
of
two
-stage
gas
generation
presented
by
Fair
and
Moore
(1936).
This
function
is
represented
by
a
discontinuous
unimolecular
reaction,
defined
as
a
constant
rate
of
increase
followed
by
a
discontinuous
equation
of
constant
rate
increase.
These
equations
are
depicted
as
follows:
First
stage:
dG/
dt
=
K
L
G
and,
Second
stage:
dG
t
dt
where
G
is
the
gas
produced
in
time,
t;
=
-K
2
G
t
G
t
is
the
gas
remaining
to
be
produced
after
the
decomposition
has
proceeded
for
time,
t;
and
K
is
the
gas
generation
constant.
In
analyzing
solid
waste
decomposition,
components
based
upon
the
relative
ease
decomposition
are
then
assigned
to
each
lives.
Selection
of
half-lives
is
not,
the
waste
is
normally
broken
into
several
of
degradation
of
the
materials.
Rates
of
component,
normally
in
the
form
of
one-half
at
present,
a
very
rational
procedure
and
values
will
range
quite
widely
from
one
investigator
to
another.
For
example,
at
Palos
Verdes
(USEPA,
1976)
half
lives
of
1,
2,
&
20
years
were
selected
for
three
categories
of
decomposables
-
readily
decomposible
(food,
grass,
etc.),
moderately
decomposible
(paper,
wood,
textile),
and
refractory
(plastic,
rubber).
The
City
of
Los
Angeles
(1976)
elected
to
use
half
lives
ranging
from
7-10
years
for
readily
decomposible
material
at
the
Sheldon
-Arleta
landfill.
Pacey
(1976)
employed
a
range
of
values
from
1/2
to
1
1/2
years
for
readily
decomposible
material
and
5
to
25
years
for
moderately
decomposible
material.
Results
of
kinetic
analyses
are
qualitatively
depicted
in
Figures
2a
and
2b.
Based
on
total
gas
production
estimates,
a
family
of
curves
may
be
derived
and
the
128
FIGURE
2a
THEORETICAL
TWO
-STAGE
GAS
GENERATION
THREE
WASTE
CATEGORIES
Moderately
Decomposible
Refractory
PRODUCED
IN
T
>
cn
Readily
Decomposible
TIME
ELAPSED
AFTER
FILL
COMPLETION
FIGURE
2b
THEORETICAL
RATES
OF
LANDFILL
GAS
GENERATION
RATE
OF
GAS
GENERATION
-
(SCF/YR)
3
SCF/LB
SCI
7
LB
6
SCF/LB
TIME
ELAPSED
AFTER
FILL
COMPLETION
129
period
of
productive
use
of
the
landfill
may
be
estimated.
To
date,
little
experi-
ence
has
been
gained
with
these
estimating
techniques.
Also,
little
data
is
avail-
able
on
total
gas
production
and
gas
production
rates
at
existing
landfills.
General
observations
of
landfills
suggest
generation
rates
ranging
from
0.06
to
0.23
SCF/lb
refuse/year.
Gas
Recovery
The
recovery
of
generated
methane
gas
in
landfills
is
of
paramount
concern
in
assessing
landfill
energy
recovery
systems.
There
are
numerous
sources
of
gas
loss
in
a
landfill.
Since
methane
production
may
start
as
early
as
six
months
after
placement
and
rates
of
gas
production
are
normally
high
in
the
early
stages
of
decomposition,
the
time
lag
between
fill
replacement
and
commencement
of
recovery
can
be
significant.
Loss
of
gases
to
the
surrounding
environment
occurs
by
convect-
ive
flow
due
to
pressure
gradients
and
by
molecular
diffusion
due
to
low
gas
concen-
tration
regions
(California,
1967).
In
a
landfill
where
the
compacted
solid
waste
and
surrounding
soil
are
of
high
permeability,
the
gas
migration
is
due
to
convect-
ive
flow
(California,
1967;
Bishop,
1965;
Van
Bavel,
1952).
Finally,
substantial
amounts
of
gas
may
not
be
recovered
from
landfills
as
a
result
of
economy
in
continu-
ing
recovery
operations
after
production
rates
fall
off
in
later
years.
Based
upon
early
experience
in
landfill
gas
recovery,
it
is
estimated
that
only
10
to
50%
of
the
theoretical
gas
produced
will
be
extracted
(Pacey,
1976),
and
that
figure
does
not
include
energy
requirements
needed
to
extract,
clean,
and
market
the
gas.
Extraction
The
principal
method
utilized
for
gas
recovery
is
by
pumping
from
recovery
wells
in
a
manner
analogous
to
extracting
groundwater.
Pumping
will
establish
a
pressure
gradient
within
the
landfill
causing
the
gas
to
flow
into
the
well.
At
the
same
time,
it
may
create
enough
negative
pressure
to
allow
atmospheric
gases
to
penetrate
the
cover
soil.
Aerobic
environments
that
would
be
established
in
an
over
-
pumped
landfill
will
not
only
be
detrimental
to
methenogenesis,
but
also
will
gener-
ate
increased
concentrations
of
CO
2
which
will
result
in
poorer
quality
of
the
with-
drawn
landfill
gases.
The
yield
of
gas
from
a
particular
portion
of
landfill
when
tapped
or
pumped
at
a
given
rate
will
be
governed
by
several
factors
including
gas
130
production
rate,
refuse
permeability,
and
cover
integrity.
The
development
of
an
effective
gas
withdrawal
system
requires
experimental
evaluation
of
the
following
factors:
a.
selection
of
a
withdrawal
rate
that
can
produce
landfill
gases
with
maximum
(and
approximately
constant)
heating
values,
b.
establishment
of
adequate
pressure
gradients
to
assure
scavanging
of
land-
fill
gases
without
interference
with
adjacent
wells,
c.
optimization
of
energy
required
for
withdrawal
of
gases,
and
d.
determination
of
number
and
location
of
wells
in
a
landfill.
In
order
to
achieve
these
goals,
a
test
well
and
supporting
monitoring
wells
must
be
drilled
and
a
series
of
static
and
short
-run
tests
performed
in
order
to
evaluate
landfill
pressure
profiles
(static
and
dynamic),
gas
composition
and
heating
values,
and
stability
of
withdrawal
rates.
Long
term
tests
(150-180
days)
are
also
conduct-
ed
to
provide
information
on
reliability,
quality,
and
quantity
of
gas
production
from
a
given
site.
The
radius
of
influence
of
a
given
well
is
dependent
upon
gas
withdrawal
rates,
depth
of
well,
permeability
of
the
refuse,
well
geometry,
and
pressure
gradients.
It may
be
computed
in
a
manner
similar
to
that
for
ground
water
wells
using
the
relationships
developed
by
Kozeny
(Muskat,
1937).
Once
operational
curves
are
developed,
extraction
well
numbers
and
locations
can
be
established.
A
typical
gas
recovery
well
is
sunk
within
a
drilled
shaft
usually
30
to
36
inches
in
diameter.
Normally,
the
lower
80%
of
the
well
is
perforated,
utilizing
alternating
four
and
six
inch
diameter
PVC
pipe
coupled
with
burlap
joints.
The
well
shaft
is
filled
in
with
clean
crushed
rock
except
for
the
upper
portion
of
the
casing
which
may
be
backfilled
with
clay.
Collection
manifolds
are
then
constructed
to
connect
the
wells,
bringing
the
gas
to
a
common
collection
site.
Gas
Utilization
and
Preparation
The
low
BTU
raw
gas
from
landfills
(normally
about
500
BTU/SFC)
is
contam-
inated
with
carbon
dioxide,
hydrogen
sulfide,
water,
and
other
decomposition
pro-
ducts.
Once
methane
gas
yields
are
established,
consideration
must
be
given
to
the
most
effective
ways
of
utilizing
it.
There
are
several
methods
currently
being
considered
for
the
utilization
of
landfill
gas
(Table
IV).
131
Table
IV
Methods
of
Utilizing
Landfill
Gas
A.
Direct
use
of
low
BTU
gas
with
minimal
cleaning
1.
Injection
into
existing
natural
gas
transmission
lines
2.
Delivery
to
adjacent
interruptible
gas
consumer
3.
On
-site
generation
of
electrical
power
B.
On
-site
gas
cleaning
to
high
BTU
gas
for
direct
pipeline
use
(
1002
methane)
C.
On
-site
conversion
of
landfill
methane
to
methanol
D.
On
-site
conversion
of
methane
to
liquified
natural
gas
The
first
category,
use
of
the
low
BTU
gas
with
minimal
cleaning,
represents
a
low
capital
investment.
Direct
use
of
raw
gas
for
pipeline
transmission
will
normally
require,
at
minimum,
dehydration
and
possible
removal
of
toxics
for
rea-
sons
of
corrosion
and
safety.
There
may
also
be
problems
with
state
utility
commis-
sion
regulation,
as
well.
Direct
use
for
electric
power
generation
has
been
demon-
strated
at
the
Sheldon
-Arleta
landfill
in
Los
Angeles
with
considerable
success
in
producing
a
substantial
recovery
of
net
energy
(Los
Angeles,
1976).
Cleaning
of
landfill
gas
to
meet
pipeline
quality
synthetic
natural
gas
will
require
substantial
investment
in
capital
equipment.
Currently,
a
1.0
MMSCF
experimental
purification
plant
employing
dehydration
and
molecular
sieves
for
H
2
S
and
CO
2
adsorption
is
in
operation
at
Palos
Verdes
landfill
in
California
(USEPA,
1976).
Net
energy
recovery
at
this
plant
has
been
lower
than
expectations,
but
another
year
of
operation
is
warranted
before
final
conclusions
can
be
drawn.
The
last
two
options,
on
-site
conversion
of
methane
to
methanol
or
liquified
gas,
are
relatively
expensive,
and
may
be
limited
to
landfills
with
high
gas
deliverability.
Gas
cleaning
techniques
include
dehydration
to
reduce
corrosion
and
absorption,
liquefaction
and
adsorption
processes
for
bulk
removal
of
CO2
and
H2S
impurities.
A
number
of
gas
purification
processes
are
commercially
available
and
have
had
long
use
in
the
petroleum
and
energy
production
industry
(Kohl
and
Riesenfeld,196oponhebeq,
1964;
Campbell,
1970).
Table
V
reviews
some
of
the
most
important
techniques.
Current
Experience
with
Landfill
Gas
Recovery
Although
there
are
a
number
of
projects
currently
underway
in
the
U.S.
extracting
and
utilizing
landfill
gases,
the
literature
is
currently
difficult
to
find.
Most
prominent
among
the
current
projects
are
those
being
carried
out
in
California.
A
brief
description
of
three
of
the
projects
is
given
below.
132
Table
V
Gas
Purification
Processes
Objective
Processes
Removal
of
Water
Absorption
by
hygroscopic
liquids
Vapor
diethylene
or
triethylene
glycol
salt
brine
Adsorption
in
activated
solid
dessicents
molecular
sieve,
activated
carbon
silica
gel,
activated
alumina
Condensation
by
compression/cooling
Removal
of
Absorption
Contaminants-H
2
S
,
CO
2
Monoethan
olamine
(MEA)
Diethanol
Amine
(DEA)
Diglycalamine
(DGA)
Hot
Potassium
Carbonate
Adsorption
Molecular
sieve,
activated
carbon
Silica
gel,
activated
alumina
CO
2
Liquifaction
Palos
Verdes
(Los
Angeles
County)
Landfill
(USEPA,
1976)
As
a
result
of
energy
shortages
and
increased
prices
for
natural
gas,
the
Los
Angeles
County
Sanitation
Districts
(LACSD)
instituted
a
research
program
in
1972
at
the
289
acre
Palos
Verdes
landfill
aimed
at
recovering
gas
for
useful
purposes.
The
Southern
California
Gas
Company
indicated
an
interest
in
the
gas
if
it
could
be
purified
economically
to
meet
pipeline
standards
of
1000
BTU/SCF.
A
contract
was
developed
with
Reserve
Synthetic
Fuels,
Inc.
(RSF)
in
1973
whereby
the
LACSD
was
to
provide
1000
SCFM
of
unprocessed
gas
to
a
purification
facility.
The
purified
gas
would
then
be
purchased
by
Southern
California
Gas
Co.
The
USEPA
in
cooperative
effort
with
the
LACSD
and
Camp,
Dresser
&
McKee
have
initiated
a
case
study
on
this
landfill
gas
project.
Seven
wells,
approximately
110
ft
deep
and
spaced
at
500
ft
centers,
have
been
placed
at
the
landfill;
only
6
have
been
used
to
supply
the
required
1000
SCFM.
The
average
gas
composition
for
a
well
producing
320
SCFM
was
53
percent
CH
4
with
CO
2
being
the
major
impurity
(45
percent).
The
average
heating
value
was
500
BTU/
SCF.
Gas
cleaning
was
provided
by
RSF's
1.0
MMSCF
purification
plant
consisting
of
dehydration
by
cooling,
pretreatment
for
H
2
S
and
free
water
removal
in
two
molecular
sieve
towers,
followed
by
six
molecular
sieve
adsorption
towers
to
remove
CO
2
.
Regeneration
of
the
pretreat
towers
was
by
a
thermalswing
cycle,and
regenera-
tion
of
the
CO
2
adsorption
towers
was
by
a
pressure
-swing
cycle.
133
Development
tests
to
date
indicate
that
approximately
0.75
SCF
of
gas
will
be
extracted
at
the
well
per
pound
of
refuse
at
a
rate
of
approximately
0.12
SCF/pound/
year.
Refuse
composition
in
the
4
year
old
fill
ranged
from
0.4
to
14
percent
carbon
and
3.5
to
56
percent
volatile
solids
on
a
dry
weight
basis.
The
average
moisture
content
was
about
30
net
-
rent
(wet
weight).
At
the
present
time
over
15
x
10
6
tons
of
solids
wags
have
been
deposited
in
this
landfill.
Gas
production
to
date
has
been
disappointing
owing
to
operational
difficulties
primarily
due
to
corrosion
problems
caused
by
carbonic
acid.
During
264
working
days,
the
system
was
under
operation
for
only
204
days.
During
the
first
four
months,
50
percent
by
volume
of
the
raw
gas
extracted
was
produced
as
pure
methane,
but
after
that
time
this
ratio
dropped
to
values
between
12
and
27
percent
due
to
infiltration
of
air.
In
nine
months
of
operation,
four
resulted
in
a
net
methane
loss
and
the
average
net
energy
gain
was
38
percent
of
that
produced.
Thus,
for
the
91,300
MSCF
of
raw
gas
produced,
31,800
MSCF
of
methane
were
produced
and
11,900
MSCF
of
methane
were
sold.
Since
this
project
is
in
its
infancy,
it
is
too
early,
yet,
to
assess
the
potential
of
this
concept
of
gas
recovery.
Sheldon
-Arleta
(City
of
Los
Angeles)
Landfill
(Los
Angeles,
1976)
The
36.4
acre
Sheldon
-Arleta
landfill
site
has
received
over
3
x
10
6
tons
of
solid
wastes
between
1962
and
1974.
Gas
migration
problems
in
1967
resulted
in
the
construction
of
a
gas
extraction
system
consisting
of
18
wells
and
header
which
carried
the
gas
to
a
fume
combustion
unit
for
odor
control.
In
1974,
the
Bureau
of
Sanitation
(City
of
Los
Angeles)
and
Department
of
Water
and
Power
participated
in
a
joint
demonstration
project
at
this
landfill.
Electrical
power
was
generated
utilizing
a
300
horsepower
internal
combustion
engine
to
drive
a
200
kilowatt
generator.
The
engine
used
a
total
raw
gas
flow
of
approximately
82
SCFM
(dry)
resulting
in
a
thermal
efficiency
of
approximately
20%.
The
gas
composition
was
50%
methane
and
had
an
average
heat
value
of
500
BTU/SCF.
Studies
of
the
landfill
gas
potential
indicated
that
approximately
0.9
SCF
of
methane
per
pound
of
refuse
over
a
10
year
period
would
be
produced
(approximately
525
x
10
6
cu
ft
of
methane
per
year
for
10
years
at
this
site).
Gas
composition
presently
is
57
percent
methane
and
43
percent
CO
2.
The
landfill
has
an
average
134
depth
of
100
ft
and
moisture
content
is
estimated
at
25
percent
(wet).
Currently,
plans
are
being
made
to
deliver
the
raw
landfill
gas
under
press-
ure
to
a
power
generation
plant
9000
feet
away.
The
plans
call
for
two
250
horse-
power
gas
compressors
-
heat
exchange
packages
which
will
deliver
1650
SCFM
of
gas
at
64.4
psia
at
325
°
F.
The
gas
will
be
cooled
to
58
°
F
to
remove
sufficient
mois-
ture
prior
to
being
piped
to
the
power
station.
The
gas
extraction
system
will
consist
of
14
deep
gas
wells
at
400
foot
centers.
Initial
cost
analyses
indicate
that
the
project
will
pay
for
itself
in
less
than
two
years
based
on
the
current
cost
of
fuel
oil.
Shoreline
Regional
Park
(Mountain
View,
California)
(USEPA,
1975)
Currently,
a
USEPA
demonstration
project
is
being
undertaken
at
the
Shoreline
Regional
Park
landfill,
a
550
acre
site
which
will
contain
4.3
x
10
6
tons
of
solid
wastes
at
an
average
depth
of
40
feet.
The
compacted
refuse
from
both
municipal
and
industrial
sources
contains
approximately
37
percent
volatile
decomposable
matter
and
it
is
estimated
that
1.8
SCF
of
gas
can
be
collected
per
pound
of
refuse
from
this
site.
It
is
intended
to
evaluate
the
site
potential
for
gas
recovery
and,
then,
to
examine
several
alternative
modes
of
utilization
of
the
gas
produced.
These
processes
will
include
all
the
methods
presented
in
Table
V
except
(D).
Little
data
is
available
currently
at
this
site.
In
this
40
foot
deep
land-
fill,
results
to
date
suggest
that
best
withdrawal
points
for
the
wells
are
at
the
bottom
of
the
cell.
After
3
years
of
decomposing,
it
has
been
found
that
the
cells
are
not
entirely
anaerobic;
therefore,
long
range
testing
must
be
undertaken
to
estimate
total
gas
production.
It
was
also
found
that
the
landfill
is
greatly
stratified,
resulting
in
excellent
lateral
gas
movement,
but
poor
vertical
disper-
sion.
Summary
Evaluation
After
reviewing
the
current
state-of-the-art
of
landfill
gas
recovery,
it
is,
perhaps,
apparent
that
it
is
yet
too
early
to
draw
final
judgments
on
the
merits
of
this
energy
source.
It
is
obvious
that
the
decision
as
to
whether
such
a
project
will
be
successful
must
be
considered
on
a
case
by
case
basis,
and
only
after
a
135
careful
exploratory
study
has
been
performed.
The
case
against
landfill
gas
recovery
systems,
based
upon
current
landfill
practice,
is
a
strong
one.
The
waste
is
heterogenous
in
chemical
composition
and
physical
properties.
Much
of
it
is
unavailable
for
active
decomposition
owing
to
the
way
it
is
placed
within
the
landfill.
Toxic
compounds
in
municipal
and
industrial
solid
wastes
may
be
inhibitory
to
the
process
of
methanogenesis.
The
landfill
does
not
serve
as
an
ideal
"reactor"
for
efficient
decomposition.
It
provides
less
than
optimal
conditions
for
biological
reaction;
the
moisture
content
is
low;
temperature
swings
are
wide
and
normally
below
optimal
values;
stratifica-
tion
of
compacted
material
is
common,
resulting
in
pockets
of
biological
activity
and
inefficient
contact
between
organisms
and
decomposable
components;
and
gas
production
is
unpredictable
owing
to
landfill
practices,
site
characteristics,
and
cover.
Finally,
net
energy
recovery
from
landfills
is
relatively
poor.
For
example,
it
is
estimated
for
a
typical
U.S.
solid
waste
(Table
I)
that
approximately
9.1
SCE
of
landfill
gas
could
be
generated
theoretically
per
pound
of
dry
refuse
with
an
energy
content
of
500
BTU/SCE
(this
is
4500
BTU/lb,
often
quoted
as
the
energy
con-
tent
of
raw
refuse).
At
Palos
Verdes,
it
was
estimated
that
0.75
SCE
of
gas
could
be
extracted
per
dry
pound
of
refuse
and
estimates
at
Sheldon
-Arleta
were
about
1.8
SCE/lb.
This
means
a
recovery
of
from
8
to
20
percent of
the
original
available
energy.
If
one
deducts
energy
costs
for
extraction
and
cleaning
for
high
purity
gas,
only
about
3
percent
of
the
theoretical
energy
of
the
solid
waste
would
be
available
as
in
the
case
of
Palos
Verdes.
Substantially
higher
recoveries
would
be
realized
for
on
-site
power
generation,
however.
Yet,
despite
these
apparent
shortcomings,
landfill
gas
extraction
projects
are
showing
promise.
To
date
these
promising
results
are
restricted
to
unusually
deep
landfill
sites
near
large
population
centers.
Economy
of
scale,
too,
plays
an
important
role
in
the
apparent
success
of
gas
recovery
projects.
Based
on
current
technology,
perhaps
only
1000
sites
in
the
U.S.
could
succeed
economically
in
such
an
endeavor.
No
effort
was
made
to
discuss
costs
at
this
point
in
time
for
several
reasons.
136
Cost
data
is
meager
and
transfer
of
technology
to
landfill
gas
extraction
is
not
complete.
Future
costs
of
oil,
gas,
and
other
fuels
is
unpredictable
and
costs
of
technology
in
this
field
will
likely
change
rapidly,
as
well.
Electrical
generation
at
Sheldon
-Arleta
was
economically
successful
and
estimates
for
future
projects
there
are
encouraging.
Gas
cleaning
to
achieve
pipe
line
quality
has
been
economically
unsuccessful
but
more
time
is
needed
to
reassess
these
costs.
A
final
point
should
be
made
regarding
the
future
of
this
energy
source.
Although
current
landfill
practices
are
not
achieving
optimal
gas
recovery
conditions,
future
practices
could
do
much
to
improve
the
situation.
Shredding
of
refuse
and
segregation
would
greatly
improve
availability
of
decomposables
to
bacterial
reaction.
Addition
of
moisture
to
landfills
(for
example,
via
leachate
recycle),
pH
control,
and
proper
landfill
management
may
produce
more
favorable
environments
for
methano-
genesis.
Many
of
these
concepts
are
already
being
put
into
practice
and,
as
energy
costs
rise
and
available
sources
dwindle,
we
may
see
a
brighter
future
for
landfill
gas
extraction.
Literature
Cited
Anderson,
D.R.,
and
Callinan,
J.P.
:
Gas
Generation
and
Movement
in
Landfills.
In:
Industrial
Solid
Wastes
Management,
Proceedings
of
National
Industrial
Solid
Wastes
Management
Conference,
University
of
Houston, Houston,
Texas,
pp.
311-316,
1970.
Bell,
J.M.:
Development
of
a
Method
for
Sampling
and
Analyzing
Refuse.
Ph.D.
Thesis,
Purdue
University,
Lafayette,
Indiana.
January,
1963.
Beluche,
R.:
Degradation
of
Solid
Substrate
in
a
Sanitary
Landfill.
Ph.D.
Thesis,
Univ.
of
Southern
California
at
Los
Angeles,
California,
1968.
Bevan,
R.E.
:
Notes
on
the
Science
and
Practice
of
the
Controlled
Tipping
of
Refuse.
The
Institute
of
Public
Cleansing,
1967.
Bishop,
W.D.,
Carter,
R.C.
&
Ludwig,
H.F.
:
Gas
Movement
in
Landfilled
Rubbish.
Public
Works,
96
pp.
64-68,
1965.
California
State
Water
Quality
Control
Board:
In
-situ
Investigations
of
Movements
of
Gases
Produced
from
Decomposing
Refuse.
Ed:
Ludwig,
H.,
Publication
No.
35,
Sacramento,
1967.
Campbell,
J.M.
:
Gas
Conditioning
and
Processing.
Campbell
Petroleum
Series,
Norman,
Oklahoma,
1970.
City
of
Los
Angeles,
Dept.
of
Public
Works,
Bureau
of
Sanitation:
Estimation
of
the
Quantity
and
Quality
of
Landfill
Gas
from
the
Sheldon
-Arleta
Sanitary
Land-
fill.
Research
&
Planning
Division
Report,
January,
1976.
Colonna,
R.A.
and
McLaren,
C.:
Decision
-Makers
Guide
in
Solid
Waste
Management.
SW
-127,
Solid
Waste
Management
Series,
USEPA,
Cinti.
0.,
1974.
Fair,
G.M.
and
Moore,
E.W.:
Heat
and
Energy
Relations
in
the
Digestion
of
Sewage
Solids
-
Mathematical
Formulation
of
the
Course
of
Digestion.
Sewage
Works
J.
137
4,
3,
pp.428-443,
May
1930.
Fungaroli,
A.A.
and
Steiner,
R.L.:
Laboratory
Study
of
the
Behavior
of
a
Sanitary
Landfill.
J.
Water
Poll.Cont.Fed.,
43,
pp.
252-267,
1971.
Golueke,
C.J.:
Comprehensive
Studies
of
Solid
Waste
Management.
3rd
Annual
Report.
SW-lOrg,
Office
of
Solid
Wastes,
US
EPA
1971.
Kotze,
J.P.,
Thiel,
P.G.,
and
Hahugh,
W.H.J.:
Anaerobic
Digestion
II.
The
Character-
ization
and
Control
of
Anaerobic
Digestion.
Water
Research,
3,
pp.
439-494,
1969.
Kohl,
A.L.
and
Riesenfeld,
F.C.:
Gas
Purification.
McGraw
Hill,
New
York,
1960.
Lin,
Y.H.:
Acid
and
Gas
Production
from
Sanitary
Landfilling.
Ph.D.
Thesis,
West
Virginia
University,
Morgantown,
West
Virginia,
1966.
Lowe,
R.A.:
Energy
Conservation
Through
Improved
Solid
Waste
Management.
SW
-125,
Solid
Waste
Management
Series,
USEPA,
Cincinnati,
Ohio,
1974.
McCarty,
P.L.:
The
Methane
Fermentation.
In:
Principles
and
Applications
in
Aquatic
Microbiology.
John
Wiley
and
Sons,
Inc.
New
York,
N.Y.,
1963.
Merz,
R.C.
and
Stone,
R.
:
Quantitative
Study
of
Gas
Produced
by
Decomposing
Refuse.
Public
Works.
99,
pp.
86-87,
November
1968.
Muskat,
M.:
The
Flow
of
Homogeneous
Fluids
Through
Porous
Media.
McGraw-Hill
Book
Co.,
New
York
1937.
Nonhebell,
G.:
Gas
Purification
Processes.
George
Newnes
Limited,
London
1964.
Pacey,
J.:
Methane
Gas
in
Landfills:
Liability
or
Asset.
Proc.
of
4th
National
Congress,
Waste
Management
Technology
and
Resource
and
Energy Recovery.
USEPA.
SW
-8p,
Solid
Waste
Management
Series,
pp.
168-190,
1976.
Quasim,
S.R.
and
Burchinal,
J.S.:
Leaching
from
Simulated
Landfills.
J.
Water
Poll.Cont.
Fed.
42,
pp.
371-379,
1970.
Ramaswamy,
J.N.
:
Effects
on
Acid
and
Gas
Production
in
Sanitary
Landfills.
Ph.D.
Thesis,
Univ.of
West
Virginia,
Morgantown,
W.Va.,
1970.
Rovers,
F.A.
and
Farquhar,
G.J.:
Infiltration
and
Landfill
Behavior.
J.Envir.Engr.
Div.
Amer.
Soc.
Civil
Engr.,
EES,
pp.
671-690,
Oct.
1973.
Smith,
F.A.:
Comparative
Estimates
of
Post
-Consumer
Solid
Waste.
SW
-148,
Office
of
Solid
Waste
Management,
USEPA,
May,
1975.
Songanuga,
0.0.0.:
Acid,
Gas
and
Microbial
Dynamics
in
Sanitary
Landfills.
Ph.D.
Thesis,
Univ.of
West
Virginia,
Morgantown,
W.Va.,
1969.
Sumner,
J.:
The
Storage
and
Collection
of
Refuse
-
Methods,
Practices,
Technical
Developments
and
Trends
-
An
International
Survey.
In:
Reports
of
the
IXth
Inter-
national
Conference
of
INTAPUC
(International
Association
of
Public
Cleansing),
Theme
I,
pp.
1-65,
Paris,
1967.
U.S.
Environmental
Protection
Agency,
NERC.
Shoreline
Regional
Park
Gas
Recovery
Pro-
gress
Report
Phase
I.
Ed:
J.A.
Carlson,
Contract
S803396-01,
Jan.31,
1975.
U.S.
Environmental
Protection
Agency,
NERC.
A
Case
Study
of
the
Los
Angeles
Sanita-
tion
Districts
Palos
Verdes
Landfill
Gas
Development
Project.
Ed:
Bowerman,
F.R.,
Rohatji,
N.K.
&
Chen,
K.Y.,
Contract
68-03-2143,
June
1976.
Van
Bevel,
C.H.M.:
Gaseous
Diffusion
and
Porosity
in
Porous
Media.
Soil
Science,
73,
pp.
91-104,
1952.
138