United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/044 August 1987
&EPA Project Summary
Retrospective Evaluation of the
Effects of Selected Industrial
Wastes on Municipal Solid
Waste Stabilization in
Simulated Landfills
Frederick G. Pohland and Stephen R. Harper
This project presents a
retrospective evaluation of a 10-year
study on the codisposal of municipal
solid waste (MSW) with selected
wastes in 19 simulated landfill cells.
The objective of the study was to
determine the effects of additions of
water, sewage sludge, buffer and
industrial wastes on the progress of
MSW stabilization by evaluation of
leachate and gas characteristics with
time. Differences between the results
from most of the landfill cells were
influenced by repeated operational
exposure to air during leachate
removal and moisture addition.
However, those cells which were
operated in a fashion most
conducive to anaerobic
methanogenesis eventually produced
the highest quantities of gas and the
least contaminated leachate. The
overall results provide a basis for
recommendations on future studies
as well as design and operational
strategies to maximize waste
stabilization at landfill disposal sites.
This Project Summary was
developed by EPA's Hazardous Waste
Engineering Research Laboratory,
Cincinnati, OH, to announce key
findings of the research project that
is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
In November 1974, a study of 19
pilot-scale simulated landfill cells was
initiated to evaluate the effect of selected
operational variables upon the rate and
ultimate degree of biologically mediated
municipal solid waste (MSW)
stabilization. Over a 10-year period,
physical and chemical analyses on
leachate and gas produced from each
cell were obtained. The objective of the
retrospective evaluation summarized here
was to ascertain the effects of the
addition of water, sewage, sludge, buffer,
and industrial wastes to the MSW
contained in each landfill cell
Preliminary Considerations
Most landfills receiving MSW proceed
through a series of rather predictable
stabilization phases whose significance
and longevity are largely determined by
climatological conditions, operational
variables, management options and
control factors operative or being applied
either internal or external to the landfill
environment. These phases can be
identified by certain leachate and gas
analyses, selecting those parameters that
best describe principal events
contributing to the progress of
stabilization during each phase.
Moreover, to direct the choice of
analyses to be used to describe a
particular phase of stabilization, it is
necessary to recognize that anaerobic
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conditions exist throughout much of the
active life of a landfill. This active life
normally extends over a period of years,
during which time certain performance
related and time dependent concepts
become evident.
As with many anaerobic biological
systems, landfills experience an initial lag
or adjustment phase which lasts until
sufficient moisture has accumulated to
encourage the development of a viable
microbial community. Thereafter, further
manifestations of waste conversion and
stabilization may be reflected by
changes in leachate and gas quality as
stabilization proceeds through several
more or less discrete and sequential
phases, each varying in intensity and
longevity according to prevailing
operational circumstances. Accordingly,
five stabilization phases may be
identified in terms of the principal events
occurring during each phase:
Phase Principal Events
I. Initial Site closue, subsidence,
Adjustment incipient aerobic
conditions
II. Transition Initial leachate
formation,
change from aerobic to
anaerobic conditions
III. Acid Active hydrolysis, acid
Formation fermentation, pH
decrease
IV. Methane Production of CH4 and
Fermentation CC>2, pH increase,
nutrient consumption,
metal complexation
V. Final Relative dormancy,
Maturation secondary fermentation,
production of humic
substances
Phases III and IV are particularly
significant; the latter Phase IV occurring
when rapid biological stabilization (RBS)
transforms intermediate products of
hydrolysis and acid formation (Phase III)
to CH4 and C02. The facility of the
associated indicator parameters to detect
and describe the presence, intensity, and
longevity of these phases is illustrated in
Figure 1.
All of the principal events selected to
describe and separate these stabilization
phases are encountered at one time or
another in landfills containing MSW,
provided that the associated microbially
mediated processes have been
augmented by a sufficiency of moisture
and nutrients and are not exposed to the
inhibitory influences of toxic materials.
However, the manifestations of these
phases often overlap within the usual
landfill setting, since no landfill has a
single "age", but rather a family of
different ages associated with the
development of various sections or cells
within the landfill complex and the
progress of each toward stabilization.
Moreover, the rate of progress through
these phases may vary depending on the
physical, chemical, and microbiological
conditions developed within each section
with time, and leachate and gas analyses
often reflect the merging of conditions in
each discrete section.
These concepts provided the basis for
a separate interpretation of results from
each of the 19 individual cells as well as
a more specific comparison of groups of
cells (e.g., indoor, outdoor water-only,
and codisposal cells) in terms of the
effects of operational variables on solid
waste stabilization rates and the
composition of leachates produced. In
the latter analysis, comparisons are
provided for peak, pre-RBS, and final
concentrations of each monitoring
parameter.
Experimental Procedures
The 19 simulated landfill cells were
constructed of 1.83-m diameter steel
tubes, 3.6 m in height, and with an
overall volume of 9.5 m3. The sidewalls
of the cells were coated with a coal-tar
epoxy, and the bottoms were made water
tight by fitting the cells with a Fiberglas
liner. Each cell was placed on a concrete
slab, filled to a height of 0.15 m with
silica.gravel, filled further with
approximately 2.4 m (eight 0 3-m lifts)
of MSW plus codisposal additives, and
then by cover layers of 0.3-m silty clay
and 0 3-m pea gravel. Gas probes were
installed at three depths; two gas probes
were placed above the second and sixth
MSW lifts, and another in the upper pea
gravel layer. Temperature probes were
placed above tho swoncl, tumlh, and
sixth MSW lifts.
A water distribution ring placed in the
upper pea gravel layer provided for the
application of infiltration water, and
individual pipes at the bottom of each
cell and connected to a central well
provided for the collection of leachate
Four of the cells were housed indoors
where maintenance of water and gas
tight seals was facilitated, and
temperatures were more conducive to
enhanced anaerobic biological
stabilization. AJI of the remaining cells
were outdoors and underground.
The MSW was loaded to the cells in
eight lifts. Codisposal additives were
evenly distributed and placed atop each
of the last seven lifts. Each lift was
compacted after loading with a wrecking
ball; densities of in-place MSW varied
from 470 to 800 kg/m3 with variations
arising primarily from differences in the
wet weight of the codisposal additive.
The weight of MSW and codisposal
additives placed in each cell are listed in
Table 1 along with their respective
moisture contents.
Two MSW samples were obtained
from each of the eight lifts in each cell
and characterized with respect to the
percentage (wet weight) for the 10 waste
categories indicated in Table 2. Samples
from each separated category were then
analyzed for a number of chemical
parameters.
The six industrial waste additives
selected for codisposal included
petroleum refinery oil/water separator
sludge, neutralized lead/acid battery
waste sludge, electroplating (Cr, Ni, Cd,
Cu, Fe, Zn) sludge, inorganic (titanium
dioxide) pigment waste, mercury cell
chlorine brine sludge, and solvent-
based paint sludge
Leachate and gas samples were
collected monthly just prior to moisture
additions and analyzed for quantity and
quality. Leachate samples were analyzed
for COD, TOC, TKN, total phosphorus,
total volatile acids, total solids, total
alkalinity, pH, specific conductivity, and a
number of metals including cadmium,
chromium, copper, iron, lead, mercury,
nickel, and zinc. Gas samples were
removed from the cells by means of a
vacuum pump and drawn into sampling
burets from which a representative
portion was obtained with a syringe for
injection into a GC. Gas volumes were
measured by collecting the gas in plastic
bags and pumping the gases through a
wet-test meter with a vacuum pump.
Gas samples were analyzed for percent
CH4, CO2, N2 and O2
Results and Discussion
Interpretations of individual simulated
landfill cell behavior were based upon
organic indicators, pH, specific
conductivity, and metals data. Of
additional importance were temperature
and moisture related parameters
including infiltration volumes applied,
leachate volumes collected, and the
moisture retained by the waste mass.
The analyses of cell behavior also
' include pertinent information reported
during cell unloading and final disposal
operations. This analysis revealed that for
most of the cells, much of the solid waste
was loaded while still in intact plastic and
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1.0
0.8
0.6
I
w
5
1 0.4
0.2
0.0
200 400
Stabilization Time. Days
Figure 1. Changes in selected indicator parameters during the phases of landfill stabilization.
X
O)
Q
O
(o
0.
600
paper bags. Therefore, much of the
waste, including the garbage and
vegetative matter, was protected and
remained relatively unaltered even after
10 years residence in the test cells.
Although the contents of the landfill cells
appeared as a black, tar-like mass,
many recognizable articles remained
intact.
Some of the research objectives
originally conceived for the research
proved unattainable, primarily because of
operational differences between sealed
and vented cells which obscured the
effects of the codisposal variables
intended for study. In particular, the
failure of gas seals and the intentional
placement of gas vents atop some of the
outdoor cells led to the regular
introduction of air into most cells during
leachate drainage and water addition
operations. This prevented or delayed
the establishment and maintenance of
anaerobic conditions necessary for
methanogenesis and rapid biological
stabilization (RBS) and, thereby, retarded
the stabilization of the waste mass and
the associated reduction in leachate
strength over time. Accordingly, the
majority of change in leachate
characteristics for many of the cells was
caused by solubitization and washout of
high concentrations of waste
constituents. This transfer of waste
constituents without biologically
mediated stabilization is undesirable
because it would result in greater
leachate treatment requirements and
potential for leachate migration and
environmental impairment.
The indoor cells, which were kept
more anaerobic and at warmer
temperatures, stabilized fastest and,
therefore, eventually produced the least
quantities of leachate-transported
contaminants Conversely, the outdoor
air-exposed cells took longer to
approach or reach rapid biological
stabilization (RBS) or methanogenesis
and, therefore, produced higher
quantities and more dramatic washout of
leachate contaminants
Conclusions
The importance of rapidly establishing
and maintaining stable anaerobic
biological conditions (i.e., RBS) was
clearly illustrated by the results of this
study. The cells which were operated in a
fashion most conducive to
methanogenesis produced the highest
amounts of methane, while also yielding
the most stabilized and lowest strength
leachates The effects of the codisposal
variables were directly manifested in the
characteristics of the leachates produced
in the absence of biological activity.
Simulated landfill cell design and
operation were the major variables
influencing the relative contributions of
biological and physical waste stabilization
mechanisms and the understanding of
how they are affected by codisposed
industrial wastes Since anaerobic
biological activity was inhibited in many
of the test cells, it was not possible from
this study to clearly distinguish the
effects of the codisposed wastes on
-------
Table 1.
Test
Cell
Number
1
2
3
4
5
6
7
8
9"
10"
11
12
13
14
15"
16
17
18*
19*
General Loading Characteristics of Municipal Solid Waste and Codisposal Additives Placed in the Test Cells
Codisposal Additive MSW
Type of Cell Codisposal Additive
OS
OS
OS
OS
OS
OS
OS
OS
OV
0V
OV
OV
OV
OV
OV
IS
IS
IS
IS
Water, 200 mm/yr
Water, 400 mm/yr
Water, 600 mm/yr
Water, 800 mm/yr
Sewage Sludge
Sewage Sludge
Sewage Sludge
Calcium Carbonate
Petroleum Sludge
Battery Waste Sludge
Prewetting Water
Electroplating Sludge
Inorganic Pigment Waste
Chlorine Brine Sludge
Polio Virus
Water, 400 mm/yr
Solvent-Based Paint Sludge
Water, 400 mmlyr
Water, 400 mmlyr
Wet
Weight, kg
-
-
68
204
680
91
1518
1291
1293
1190
1421
2039
-
-
1604
-
-
Moisture
Content, %
-
-
-
-
888
880
880
JO.O
790
893
1000
79.5
51.7
24 1
24.7
-
-
Dry
Weight, kg
-
-
-
8
24
82
82
319
138
0
244
686
492
-
-
1208
-
-
Wet
Weight, kg
3025
2989
3007
3002
3001
2919
2964
2994
3001
2998
2924
3048
3006
3015
3010
2996
2998
3000
3012
Moisture
Content, %
382
382
382
382
382
38.2
382
382
30.4
304
38.2
382
38.2
38.2
304
38.2
38.2
30.4
304
Dry
Weight, kg
1870
1847
1858
1855
1855
1804
1832
1850
2089
2087
1807
1883
1858
1863
2041
1852
1853
2088
2096
OS = outdoor, initially sealed.
OV - outdoor with vented or poorly fitted top.
IS = well sealed indoor.
' Cells were loaded April 1975, all others in November 1974.
biological degradation patterns Nor was
it possible to provide a clear indication of
the leachate characteristics expected
from the codisposal cells under
conditions more favorable to
methanogenesis, where leachate organic
strength is drastically reduced by
conversion to methane and carbon
dioxide, and metals are more
successfully attenuated by increased
levels of sulfides and other precipitation
mechanisms prevalent at more neutral
pH values. Therefore, determination of
acceptable codisposal loadings in terms
of attenuation and absence of inhibition
could not be made.
Since the potential influences of the
industrial wastes on biological activity
were obscured by operational practices
detrimental to methanogenesis, most of
the apparent waste mass "conversion" in
the outdoor industrial waste cells was by
washout. On the other hand, the results
from the indoor cells serve to
demonstrate the benefits of enhanced
biological activity toward reducing
potential environmental impact
associated with leachate migration and
ultimate leachate treatment and disposal
costs, and improving the recovery of
energy as biogas. The simulated landfill
cells which attained rapid biological
stabilization (RBS) most quickly
produced less than half the quantities of
leachate organic contaminants than did
cells which did not reach RBS
Recommendations
To minimize the quantities of organic
and inorganic contaminants transported
from the waste mass via leachate,
emphasis should be placed on promoting
anaerobic biological activity in MSW and
codisposal landfills. This would involve
efforts to provide anaerobic conditions,
temperature insulation, a sufficient and
uniform moisture environment, and the
minimization of isolation or restricting
layers which protect wastes from
microbial and moisture contact
To promote anaerobic conditions,
landfills should be designed to be as
contained and aa homogeneous as
possible, with the development of
individual cells and the selection and
maintenance of the containment system
receiving particular attention In addition,
MSW placement should be scheduled
such that this process is enhanced in
each landfill.
Since the results from this study did
not conclusively reveal the expected
influences of codisposed industrial
wastes, sewage sludge, and buffer,
additional studies are recommended to
more fully elucidate the potential effects
of these variables. Any future studies
should be undertaken using well
controlled landfill cells operated in a
fashion conducive to promoting rapid
biological stabilization (RBS), so that the
effects of industrial waste loadings on
biologically mediated MSW stabilization
and the associated attenuation capacity
for these loadings can be established.
In light of the Resource Conservation
and Recovery Act Amendments leading
to the banning of liquids and hazardous
wastes from landfills, and the shortage of
approved hazardous waste land disposal
sites, the industrial wastes chosen for
additional codisposal studies should be
selected in cognizance of both the total
production quantities of these wastes as
well as the quantities which may permit
safe disposal in MSW landfills
-------
Table 2. Compositional Analyses of Municipal Solid Waste Placed in Each of the Nineteen Test Cells
Waste Component, % by wet weight
Test
Cell
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
16
17
18
19
Loading Variable
Water, 200 mm/yr
Water, 400 mm/yr
Water, 600 mm/yr
Water, 800 mm/yr
Sewage Sludge
Sewage Sludge
Sewage Sludge
Calcium Carbonate
Petroleum Sludge
Battery Waste Sludge
Prewetting Water
Electroplating Sludge
Inorganic Pigment Waste
Chlorine Brine Sludge
Water, 400 mmlyr
Solvent-Based Paint Sludge
Water, 400 mm/yr
Water, 400 mm/yr
Mean"
Standard Deviation
Paper
37 1
41.5
365
378
41 2
349
43.6
53 1
41 3
44 0
398
465
39 1
37.1
41 8
45 7
483
43.2
41 8
46
Garden
Wastes
138
21 5
25.9
226
166
302
203
11 1
17.0
82
162
95
207
11 1
163
156
98
11.9
166
60
Metals
12.2
8.5
8.1
5.9
80
8.6
90
58
89
88
8.4
77
83
99
89
77
9.3
74
84
1 4
Food
9.5
6.3
6.1
59
11.3
11 0
53
66
76
112
87
82
63
90
7.3
6.0
6.2
8.5
7.9
1.9
Glass
93
99
94
88
7 1
59
64
6.4
5.3
72
9.0
88
78
8.2
6.0
66
84
10.0
7.8
1.5
Plastics,
Rubber,
Leather,
Textiles
11 2
99
6 7
105
14 9
tie
98
12 2
140
10 1
1 1 I
80
10 1
124
13.9
11 3
94
102
1 1 1
18
Fines
40
35
30
35
2.9
24
28
1 7
2 1
33
34
42
29
4 1
28
28
34
36
3 /
07
Ash,
Rock,
Dirt
33
33
35
1 4
1 6
34
29
1.6
2.8
4 7
20
6 1
1 8
4 1
1.3
2.7
30
1.9
29
1 3
Diapers
25
1.2
1.5
32
1 8
23
24
1 6
09
29
24
1 5
3 7
4.8
2.7
1 6
29
3.0
24
1.0
Wood
1.4
2.2
1 4
20
1 1
03
1 7
1.1
1 9
4 4
1 6
1 2
1 4
1.5
08
1.4
39
1.9
1 7
1 0
' The mean is based on 18 rather than 19 cells since the Compositional Analysis for Cell No 15 was not available
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Frederick G. Portland and Stephen R. Harper are with the Georgia Institute of
Technology, Atlanta, GA 30332..
Jonathan G. Herrmann is the EPA Project Officer (see below).
~fhe complete report, entitled "Retrospective Evaluation of the Effects of
Selected Industrial Wastes on Municipal Solid Waste Stabilization in Simulated
Landfills," (Order No. PB 87-198 701IAS; Cost: $24.95, subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-87/044
OC0032V PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 S DEARBORN STREET _,
CHICAGO IL 60604
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