United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-88/027 July 1988
x>EPA Project Summary
Pilot Scale Evaluation of Sludge
Landfilling: Four Years of
Operation
J. W. Stamm and J. J. Walsh
A sludge landfill simulator
program consisting of 28 lysimeters
was used to evaluate sludge
landfilling as a disposal option by
assessing the environmental impacts
on ground water, surface water, and
air quality. The disposal scenarios
investigated were codisposal, ref-
use-only, and sludge-only. All ly-
simeters were constructed in June
1982 and were housed at U.S. EPA's
Test and Evaluation Facility in
Cincinnati, OH. Thirty-four physical
and chemical parameters were
measured to document leachate and
gas quality and quantity. In addition
to the various environmental as-
sessments, certain lysimeters were
spiked with a priority pollutant solu-
tion to investigate the generation of
potentially hazardous leachate.
This study presents the results
of 4 yr of research, from July 1982
through June 1986. A complete
tabulation of data collected over the
4-yr period is included in the report
The monitoring results indicate that
codisposal of sludge and refuse
accelerated the anaerobic decom-
position processes relative to the
other disposal scenarios. The ex-
perimental variables of infiltration
rate, sludge loading rate, and sludge
type produced definitive effects on
the leachate and gas quality and
quantity. A review of leachate and
gas quality data suggests that the
codisposal of sludge and refuse may
be a superior means of disposal.
This disposal scenario had the least
detrimental effect on leachate quality
and quantity while positively affect-
ing the decomposition processes (as
measured by methane generation).
Gas chromatography/mass spec-
trometry (GC/MS) analysis of leachate
samples showed several leaching
trends exhibited by the priority
pollutants from both the sludge-only
and codisposal test cells.
This Project Summary was
developed by EPA's Water 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).
Method and Objectives
To simulate sludge landfilling as it is
commonly practiced, the program design
included pilot-scale steel tanks (or cells)
filled with municipal refuse and various
loading rates of municipal wastewater
sludges. Conceptually, each cell acts as
an independent landfill (or section from a
landfill) operated under anaerobic
conditions and according to the initial
experimental variables. For each cell,
water is added on a monthly basis to
reflect expected rainfall conditions.
Leachate is drained monthly, and
samples are collected and analyzed for
standard chemical constituents as well as
the presence of trace organic com-
pounds. Additionally, gas is quantified
and periodic samples collected for
analysis. Lastly, temperature readings are
routinely recorded to monitor changes
due to decomposition processes or
seasonal fluctuations. Under this general
program design, the simulated landfills
can be evaluated singularly or compared
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to one another under experimental
conditions corresponding to actual field
conditions.
The specific program design is
outlined in Table 1. A total of 28 cells
were filled with various sludge/refuse
ratios. These ratios included 0% sludge
(100% refuse), and 10%, 20%, 30% and
100% sludge loading rates. Other
experimental variables included the use
of two different sludge types, two
infiltration rates, different cell heights and
diameters, and the spiking of the sludge
in eight cells with a priority pollutant
stock solution. The project test cells were
inside at the U.S. EPA Test and
Evaluation (T&E) Facility in Cincinnati,
OH. The codisposal and refuse-only
cells (Nos. 1 through 20) were placed in
a stacked arrangement of two lower rows
of five and two upper rows of five.
Reinforced concrete footers support the
lower cells while the upper cells are
supported on a structural steel frame-
work. The sludge-only cells (Nos. 21
through 28) are smaller diameter tanks
located in front of the codisposal cells at
floor level.
The primary objective of this
program is to monitor and evaluate
leachate and gas release from sludge
landfills constructed and/or operated
under the following conditions:
1. Sludge landfills receiving anaero-
bically digested sludge versus those
receiving lime treated sludge.
2. Sludge-only landfills versus refuse-
only landfills versus codisposal land-
fills.
3. Codisposal landfills receiving various
sludge loadings (10%, 20%, and 30%
of the total sludge/refuse mass).
4. Landfills receiving low versus high
infiltration rates.
5. Shallow versus deep landfills.
6. Landfills spiked with elevated levels of
priority pollutant compounds, versus
control landfills.
Procedures
The pilot-scale test cells were
designed by SCS Engineers and
constructed by a local fabricator. The
purpose of the design was to provide a
durable, gas-tight container of sufficient
scale to promote the decomposition
processes that occur in an actual refuse,
sludge, or codisposal landfill. The cells
are rolled steel tanks, double-welded at
the seams, with two interior coatings of
rustproof, high-build epoxy sealer. The
codisposal and refuse-only cells (Nos. 1
through 20) are 1.8 m (6 ft) in diameter
and 2.7 m (9 ft) in height. Due to the
heterogeneous nature of municipal ref-
use, a greater waste volume was
selected for the codisposal cells. The
smaller sludge-only cells (Nos. 21
through 28) are 0.6 m (2 ft) in diameter;
four are 2.7 m (9 ft) tall, and the
remaining four are 1.5 m (5 ft) tall.
Required quantities of municipal
refuse were obtained from City of
Cincinnati collection vehicles and
delivered to a specially prepared
receiving area outside the T&E Facility.
The purpose here was to obtain a waste
medium that typified household refuse
generated in the U.S. A quantity of over
45 metric tonnes (50 tons) of municipal
refuse was delivered to the project site
where it was manually mixed by a
University of Cincinnati work crew. This
manual mix consisted of breaking open
all plastic bags, spreading materials, and
removing non-representative refuse
materials such as pianos, tires, and
commercial items. After the mix was
completed and prior to cell loading, a
representative 3% sample was seg-
regated from the waste mass and a
refuse characterization procedure was
performed. The refuse was manually
sorted into 14 categories that included
paper, plastic, metal, glass, and food
waste. The refuse sorting procedure was
performed to assure that the refuse
sample was not biased and represented
typical municipal refuse. In order to
further assess the physical and chemical
inputs to the cells from the refuse
quantities, refuse grab samples were
obtained for chemical composition and
moisture content analyses.
Required quantities of municipal
sludges were obtained from the Blue
Plains Wastewater Treatment Plant in
Washington, D.C. A total of about 12
metric tonnes (13 tons) of anaerobically
digested (AD) and lime-treated (LT)
sludges were loaded into 66 steel drums
with lids and delivered by truck to the
project site in Cincinnati. Samples of the
incoming sludges were obtained and
analyzed for a variety of chemical
parameters. The sludges differed signif-
icantly in composition with notably higher
levels for pH, alkalinity, and iron in the
lime treated sludge. The two incoming
sludges were also analyzed initially for
organic priority pollutants by GC/MS.
Following the placement of the
gravel drainage layers, quantities of
refuse and sludges were weighed,
loaded, and compacted in four 0.46 m
(1.5 ft) high lifts in each test cell. In the
codisposal and refuse-only cells (Nos. 1
through 20), refuse quantities were
loaded first, followed by designated
sludge types and quantities added atop
each refuse layer. The cells were loadet
on a lift-by-lift basis so that the first lit
was completed in all cells before movin;
on to the second lift. Temperature probe:
were installed atop the second lift and th<
probe lines exited through temperatun
ports. Loading activities were conductec
continuously for 4 days until the com
pletion of the fourth lift in codisposal anc
refuse-only test cells. At that time gai
ports and leachate drains were installet
and an infiltration spray nozzle was
placed on the interior of the test cell lids.
The sludge-only cells (Nos. 2
through 28) were loaded in a separate
operation and received preweighec
quantities of AD or LT sludges. Temper
ature probes, gas ports, and leachaU
drains were installed in the same manner
In designated codisposal and sludge
only cells, a solvent-based priority
pollutant spike solution was added tc
individual sludge quantities at the time o
loading. The spike solution contained the
following 12 priority pollutant compound;
in a methylene chloride carrier solvent:
Acenapthene Ethylbenzene
Benzene Naphthalene
Bis (2-Ethylhexyl) Phenol
Phthalate
1,4-Dichlorobenzene Pyrene
Dimethyl Phthalate Toluene
Di-n-butyl Phthalate PCB (Arochlor I2S
The last steps of the loading operation;
included placement of the test cell lids
final connection of gas and temperature
probes and infiltration lines, welding o
the steel lids, and pressure testing tc
ensure air and water-tight conditions
Various operation and monitorinc
activities were performed on a continuous
basis for this long-term experiment
Specifically, test cell temperatures (one
probe per test cell) were recorded on E
daily basis for the first 2 mo
Temperatures were then monitored bi-
weekly or on an "as-appropriate" basis
In addition, leachate was drained fronr
every cell each month. The volume o
leachate drained was recorded to aid ir
the compilation of a moisture balance
summary. Two representative samples
were then collected from the leachate
drained each month for each cell. The
first sample was prepared for standarc
chemical analysis and transmitted to the
University of Cincinnati. The seconc
sample was collected for GC/MS
quantitation of trace organics b}
analytical personnel at PEI Associates
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Table 1.
Program Design
Sludge Loading Priority Pollutant Infiltration Waste Height
Test Cell Sludge Type" (%)t Spiket Rate" (m)
Codisposal and
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Refuse-Only:
AD 10
LT 10
AD 10
LT 10
AD 20
LT 20
AD 20
LT 20
AD 30
LT 30
AD 30
LT 30
AD 20 Spiked
LT 20 Spiked
AD 20 Spiked
LT 20 Spiked
0
0
0
0
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
High
Low
High
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
Sludge-Only:
t
t
21
22
23
24
25
26
27
28
AD
LT
10, 20, etc., =
Spiked ~
Low =
High
AD 100
LT 100
AD 100
LT 100
AD 100 Spiked
LT 100 Spiked
AD 100 Spiked
LT 100 Spiked
Low
Low
Low
Low
Low
Low
Low
Low
Anaerobically digested sludge (16 percent solids);
Lime-treated sludge (16 percent solids).
Percent ("/<>) sludge addition by wet weight of sludge/refuse mixture.
Received solvent-based spike containing twelve priority pollutants.
Receives an annual water infiltration rate of 0.500 Ukg of cell waste
and/or sludge) on a dry weight basis;
Receives an annual water infiltration rate of 1.000 Ukg of cell waste
and/or sludge) on a dry weight basis.
0.6
0.6
1.8
1.8
0.6
0.6
1.8
1.8
(refuse
(refuse
During project start-up, changes in
project scope and budget precluded the
monitoring of three compounds. These
compounds were benzene, ethyl ben-
zene, and toluene.
Infiltration water was applied to every
cell each month immediately after the
leachate had been drained as described
above. The volume added was based on
an annual rate applied against the total
quantity (dry weight) of wastes present in
each cell. Cells received either the low
infiltration rate (similar to Midwest U.S.
percolation estimates) or the high
infiltration rate (twice the low rate). The
low infiltration rate was equivalent to 0.5
L of water/kg of waste/yr. The high
infiltration rate was equal to 1.0 L of
water/kg of waste/yr. Inspection and
maintenance activities were also
employed each month for general
housekeeping purposes and to ensure air
and water tightness in all cells.
Monitoring activities centered on
providing physical/chemical descriptions
of the in-place wastes, infiltration water,
product gases, and generated leachates.
Standard chemical analyses performed
on leachate samples in the laboratory
included pH, alkalinity, volatile acids, total
-------
and volatile solids, total organic carbon
(TOC), chemical oxygen demand (COD),
total Kjeldahl nitrogen (TKN), total
phosphate, chlorides, sulfide, seven
metals, and trace priority pollutants. In
conjunction with the above analyses,
gases generated from the cells were
sampled each month and analyzed by
gas chromatography for methane, carbon
dioxide, nitrogen, and oxygen contents.
Discussion of Results
The investigation has produced a
great quantity of information on the
behavior of the 34 parameters measured.
An in-depth analysis of each of these
parameters would have produced a
report of unreasonable size. Conse-
quently, the report presents general and
obvious trends and includes all raw data
in the Appendices. In this manner, major
findings are made available as well as
the total data set, allowing other
investigators to explore specific aspects
of the results in greater detail. The
presentation and discussion of results
below follow the outline of objectives
presented earlier.
Sludge Type
The type of sludge that is placed in
a landfill will have a direct effect on the
generation of leachate. A comparison of
the two sludge types showed that AD
sludge posed less of a negative impact
on leachate quality than LT sludge.
These effects were more dramatic in the
sludge-only than the codisposal cells.
A comparison of sludge types
showed that the pH range among the
codisposal cells was approximately 0.5
pH units through the first 2 yr. This range
began to show signs of shrinking in the
third year. Occasionally, higher pH
values were detected as remaining
pockets of lime were leached from the
lime-treated codisposal cells. The two
sludge types caused a dramatic
difference in pH between the two types
of sludge-only cells. The AD cells
averaged a pH of 6 while the LT cells
had a mean pH level above 9 with some
values above 10 units. These trends
generally continued throughout the rest
of the monitoring period.
Table 2 presents a summary of
leachate quality parameters for both
codisposal and sludge-only cells. The
parameters presented in this table are
4-yr mean values for selected AD and
LT cells. Specific volume in this and
subsequent tables is leachate quantity
(Ukg/mo). All treatment conditions for the
sets, except cell type, were the same. A
review of this data reinforces the
conclusion that AD sludge produces a
leachate that is relatively more benign
than LT sludge. The effect is larger for
the sludge-only cells than for the
codisposal cells.
In the sludge-only cells, the
leaching of lime lowered the pH in the LT
cells and allowed a resurgence of activity
of microorganisms. This activity can be
measured by many of the leachate pa-
rameters. This data showed an increase
of volatile solids production in the LT cell
while its anaerobic counterpart displayed
a variable but normal decline in volatile
solids levels. Over the 48-mo exper-
iment, the average leachate composition
for these 2 cells differed by over 3,000
mg/L of volatile solids. Also, these cells
showed a sharp increase in volatile acid
production during the close of the
second year. An examination of COD
levels for LT cells showed a steadily
increasing level of COD in its leachate.
By comparison, the anaerobic
counterparts actually show a gradual
decrease in COD levels. Over the 48-
mo period, the average for the 2 sludge
types differed by over 12,000 mg/L of
COD.
A final point for consideration is the
effect on microbiological activity as
measured by methane generation.
Though both sludges initially accelerated
methane production, LT sludge tended to
stall methane generation shortly there-
after. Initially, this appears to be a
desirable effect, until one considers the
following. Any organic matter (refuse or
sludge) placed in anaerobic conditions
(underground) will eventually undergo
biological decomposition. This decom-
position will result in the generation of
methane. From the viewpoint of landfill
planning and operations, it is desirable to
encounter the bulk of methane gen-
eration in the early stages of operation.
At this time, methane collection and
disposal may be included in the landfill
design and become a part of daily
operations. If, however, the bulk of
methane generation occurs in the final
stages of operation, or after closure of
the landfill, the problem may go
unnoticed for some time. History has
shown that uncontrolled methane
generation and migration poses an
environmental threat as great as
ground-water contamination from
leachate migration.
Based on these trends, the type of
sludge stored in a landfill will have a
definite effect on leachate strength and
anaerobic decomposition as measurec
by methane generation. This stud\
shows that AD sludge would be superioi
to LT sludge in either a codisposal oi
sludge-only landfill.
Landfill Type
The environmental impact o
disposing of sludge in a landfill operatior
was the main thrust behind the researcf
project. The experiment was designed tc
allow a comparison between three dif
ferent types of landfills: codisposal
sludge-only, and refuse-only. An ex
amination of the experimental data shows
that the codisposal type landfill is su
perior to the other two types of landfills
The combination of sludge and refuse
tends to enhance the rate of anaerobic
decomposition. This is demonstrated ir
both leachate and gas quality.
Table 3 presents a cross-section o
leachate parameters averaged over 4 yr
This table allows the direct comparison o
codisposal vs refuse-only vs sludge
only. Other experimental variables were
held constant between the three
groupings of cells (see table legend). /
review of COD levels for the three eel
types revealed that the refuse-only cell;
produced a leachate with a COD highe
than the other two cell types by an orde
of magnitude. How-ever, the codisposa
cells were only 27% higher than the
sludge-only cells.
Using COD as a measure of leachate
strength, the codisposal cells show that <
weaker leachate was generated relative
to the other two cell types. More im
portantly, the bulk of this contaminatior
was released sooner (approximately 1 yr
than either of the other tw(
configurations. This second item i;
important when landfill designers ar<
planning for leachate collection anc
disposal. Examining the other parameter;
in Table 3, similar leaching trends hek
true for TOC and volatile solids.
An examination of the gas com
position data shows that the codisposa
cells generated methane much soone
than the refuse-only cells. This signifies
that decomposition of the waste ha(
reached advanced stages in the co
disposal cells sooner than in the refuse
only cells. As discussed earlier, methan<
collection and treatment is more effectivi
in the early life of a landfill as opposed t<
after its closure.
Based on leachate quality and ga;
generation trends, codisposal landfill:
should prove less of an environmenta
hazard than refuse-only or sludge-onl'
landfills.
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Table 2. Comparison of Leachate Parameters for Anaerobically Digested Sludge vs Lime-
Treated Sludge
Codisposal Cells" Sludge-Only Cellst
Anaerobically Lime-Treated Anaerobically
Parameter Digested Sludge Sludge Digested Sludge
COD (mg/L)
TOC (mg/L)
pH
Volatile Acids (mg/L)
Volatile Solids (mg/L)
Specific Volume (Ukg)
2,496
904
6.9
1,302
1,501
0.07
7,455
2,599
6.8
3,115
3,095
0.08
2,159
734
6.2
1,059
4,659
0.07
Lime-Treated
Sludge
14,961
5,566
8.4
9,236
7,702
0.09
" Cells 3 and 4.
t Cells 21 and 22.
Sludge Loading Rate
In this project, sewage sludge cake
(16% dry solids) was codisposed with
refuse at 10%, 20%, and 30% by weight
ratios. Comparison of these codisposal
ratios showed three distinct trends. First,
as might be expected, the effect on a
given parameter depended on the
amount of the sludge present in the cell.
This trend was quite prominent in the
first year. A second trend showed all
three loading ratios reaching a type of
equivalence point early in the second
year and showed little relative difference
in release concentrations for the
remainder of the monitoring period. The
final relationship showed a significant
increase in average leachate strength
when sludge loading was increased from
20% to 30%.
Figure 1 shows the percentage of
moisture in codisposal cells containing
anaerobically digested sludge as a
function of time. Throughout the first 12
mo of operation, all 3 cells exhibited an
increase in percent moisture. By Month
12, the gap separating the 30% cell and
the 10% cell had decreased from 6% to
*%. By Month 24, the gap separating the
3 cells was less than 3%. Generally,
these trends continued through the end
of the project. In addition, values of
leachate generated per unit mass are
presented in Table 4. These values show
that on an average of over 4 yr, monthly
leachate generation did not change as a
function of sludge loading.
Table 4 presents the effects of the
sludge loading ratio on the average of
five other leachate characteristics over
the 4-yr period. In every case except
for pH, there was an increase in leachate
strength as sludge loading was increased
from 20% to 30%. For example, TOC
levels in the AD cells increased from 879
mg/L (for 20% sludge) to 1,439 mg/L (for
30% sludge). This trend also was true for
the LT cells. COD levels increased from
4,845 mg/L (20% sludge) to 12,581 mg/L
(30% sludge).
In summary, sludge loading ratios
produced two distinct effects in leachate
strength. First, declines in a given
leachate parameter during the first year
were greater for cells with a smaller
proportion of sludge. Second, increases
in sludge loading between 20% and 30%
had profound influence on the final 4-yr
mean value for many leachate pa-
rameters.
Infiltration Rate
Infiltration rate was a controlled
variable in the experiment. Consequently
after the landfill was activated, leachate
generation should have equalled infil-
tration rate. As Table 5 shows, leachate
generation averaged over the entire 4 yr
ranged from 0.03 to 0.07 L/kg/mo, while
infiltration rates were 0.041 L/kg/mo and
0.083 L/kg/mo. The reason, for the
difference is the amount of water
required to saturate the cell contents.
As expected, the high infiltration cells
averaged roughly twice the leachate
production that low infiltration cells
experienced. This relationship was found
for both codisposal and refuse-only
cells.
Table 5 also contains a cross-
section of other test cell parameters
presented on the basis of infiltration rate.
These mean values demonstrate differ-
ences in leachate strength and are not
intended to serve as a basis for
numerical extrapolation. An examination
of this data shows that doubling the rate
of infiltration did not substantially lower
the strength of the leachate. Effects were
not the same for the codisposal and
sludge-only cells. An increased rate of
Table 3. Various Average Leachate Values for Codisposal, Refuse Only, and
Sludge-Only Test Cells
Parameter
Codisposal'
Refuse-Onlyt
Sludge-Only t
COD (mg/L)
fOC (mg/L)
pH
Volatile Acids (mg/L)
Volatile Solids (mg/L)
Specific Volume (Ukg)
2,889
903
7.1
868
2,171
0.03
22,453
4,640
6.4
7,434
7,659
0.03
2,258
737
6.2
1,213
5,555
0.07
* Average of Cell 1, 5, and 9.
t Average of Cell 17 and 19.
t Average of Cell 21 and 23.
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s
I
TC 5 (LI AD 20)
TC1 ILIAD fOI
24 30
Time (months)
Figure 1. Percent moisture vs time.
Table 4. Comparison of Leachate Parameters by Sludge Loading Ratio and Sludge Type
Anaerobically Digested Sludge* Lime-Treated Sludge*
Parameter
COD (mg/L)
TOO (mgtL)
PH
Volatile Acids (mg/L)
Volatile Solids (mg/L)
Specific Volume (L'kg)
70%
2,601
761
7.1
891
1,630
0.05
20%
2,447
879
7.0
938
7,724
0.05
30%
3,477
7,439
6.8
2,069
2,6/5
0.06
70%
6,585
2,367
7.0
2,756
3,223
0.06
20%
4.845
7.697
70
7.279
2,522
0.06
30%
72.587
4.727
68
5,747
4,579
0.06
"Values are average of LI and HI cells
Reported values are based on averaged monthly data values. Reported values are averaged over a 4-yr period.
Table 5. Comparison of Leachate Parameters as a Function of Infiltration Rate
Codisposal Cells* Refuse-Only Cells
Parameter
COD (mg/L)
TOC (mg/L)
PH
Volatile Acids (mg/L)
Volatile Solids (mg/L)
Specific Volume (Ukg)
Low Infiltration
2,556
903
7.7
868
2,777
0.03
High Infiltration
2,793
7,750
6.8
7,730
7,808
0.07
Low Infiltration
22.454
7,770
6.4
7,434
7,659
0.03
High Infiltration
19.395
6.257
6.0
7,234
6,297
0.07
* Designates all codisposal cells at a similar state of infiltration.
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infiltration generally increased leachate
concentrations for the codisposal cells,
but caused a slight decrease in leachate
strength for the sludge-only cells.
Though increased infiltration rate did
not produce a consistently stronger
leachate, the higher rate of infiltration did
increase the rate of decomposition in
refuse-only cells. The high rate refuse-
only cell generally reached 50% meth-
ane concentrations almost 12 mo earlier
than the low rate cell. In this comparison,
the levels of methane are used as an
indirect measure of decomposition
progress. This trend did not hold true for
codisposal cells. It is hypothesized that
the increased rate of infiltration brought
the refuse-only cells to field capacity
earlier, thus enhancing decomposition
processes. Because the codisposal cells
contained sludge with a high level of
moisture, codisposal cells reached field
capacity at roughly the same time
regardless of infiltration rate. In con-
clusion, an increased rate of infiltration
did increase leachate generation (as
expected). However, it did not exert a
substantial impact on leachate strength.
Waste Depth
The effects of disposal depth were
studied for the sludge-only type of
andfill in this project. The result showed
that differences in cell heights produced
only a secondary effect on certain
leachate quality and gas production
parameters.
Priority Pollutants
A review of the GC/MS data
demonstrated three main points
concerning the leaching of these target
compounds. First, the release of these
compounds from the cells was extremely
erratic. This is not surprising from a
mass transport point of view for several
reasons. First, the heterogeneous nature
of the municipal solid waste in the cells
and the intermittent flow of infiltration
water contribute to non-steady state
conditions. Second, all of these com-
pounds show a complex molecular
structure, which can allow various
chemical reactions once released within
the heterogeneous environment of the
test cell. Third, all of these compounds
have extremely low solubilities in water.
This leaves their dilution into the flow of
leachate at the mercy of the quantity of
organic solvents present in the leachate.
The second point was that the con-
centrations of the various compounds in
he leachate from the spiked cells were
•ot higher than their concentrations in
the leachate from the non-spiked cells.
The only exceptions to this rule were in
the case of dimethyl phthalate and bis(2
ethyl hexyl) phthalate, and, in the
sludge-only cells, 1,4 dichlorobenzene.
A note of caution is included as to the
significance of this statistic. The large
standard deviations cast some doubt on
the validity of comparing these two mean
values.
The third point was that the bulk of
the target compounds was released early
in the life of the project. Though the
erratic nature of the data makes con-
ventional modeling efforts impossible, a
review of the data showed that almost all
of the target compounds reached peak
leachate concentrations by the second
year.
A comparison of the mean concen-
trations of all the target compounds in
the leachate to the initial concentrations
placed in the test cells (particularly for
spiked cells) indicates that the cum-
ulative amounts of compounds that
leached out were less than the amounts
charged. Either the materials were tightly
bound in the cell contents or have been
degraded. The ultimate fate of these
pollutants cannot be determined until the
cells are opened and their contents
analyzed. The results clearly show that
rapid transfer of these complex organic
pollutants to leachate and potentially to
ground water does not occur.
Conclusions
1. The codisposal of AD sludge should
produce a lower leachate strength
than codisposal with LT sludge.
2. The codisposal of sludge and refuse
offers the optimum landfill setting
because it has the least overall effect
on leachate strength and enhances
the overall rate of decomposition.
3. Over the life of a landfilling
operation, variations in sludge cake
loading ratios less than 20% will
exert little effect on the strength of
the leachate generated.
4. An increased rate of infiltration will
not cause a corresponding increase
in leachate strength. But an
increased infiltration rate does
increase the rate of decomposition in
refuse-only cells.
5. The presence of elevated levels of
certain priority pollutants did not
cause significant increases in the
concentration of these compounds in
the resultant leachate.
The full report was submitted in
fulfillment of U.S. EPA Contract No. 68-
03-3220 by SCS Engineers under the
sponsorship of the U.S. Environmental
Protection Agency.
-------
J.W. Stamm and J.J. Walsh are with SCS Engineers, Covington, KY 41017
G.K. Dotson and J.B. Farrell are the EPA Project Officers (see below).
The complete report, entitled "Pilot Scale Evaluation of Sludge Landfilling: Four
Years of Operation," (Order No. PB 88-208 4341 AS; Cost: $25.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For further information, J.B. Farrell can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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