United States Office of Water ft sw-758
Environmental Protection Waste Management May 1979
Agency Washington D.C. 20460
Solid Waste
vvEPA Demonstrating Leachate
Treatment Report
on a Full-Scale
Operating Plant
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DEMONSTRATING LEACHATE TREATMENT
REPORT ON A FULL-SCALE OPERATING PLANT
This report (SW-758) was written
by R. L. Steiner, J. D. Keenan, and A. A. Fungaroli,
and is reproduced as received from the grantee.
U.S. ENVIRONMENTAL PROTECTION AGENCY
1979
U.S. Environr-or:*-:! Protection Agency
Rcg;on V, UN--/
230 South [;--:,.>;...-:' i':..cot
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This project was conducted at the GROWS (Geological Reclamation
Operations and Waste Systems, Inc.) landfill in Falls Township,
Pennsylvania, with partial funding from the U.S. Environmental
Protection Agency, demonstration grant No. S-803926.
Publication does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor
does mention of commercial products constitute endorsement by the U.S.
Government.
An environmental protection publication (SW-758) in the solid
waste management series.
U.S.
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CONTENTS
Page
Summary and Conclusions 1
I. INTRODUCTION - - 8
II. OVERVIEW OF LEACHATE TREATMENT OPTIONS 12
Leachate Composition 12
Leachate Treatment 22
Summary 31
11. LEACHATE TREATMENT SYSTEM 33
Design Overview 36
Design Flow 36
Design Leachate Characteristics 38
Design Concept 40
Leachate Collection System ^0
Chemical/Physical Section k2
Chemical Precipitation k2
Air Stripping of Ammonia k3
Neutralization and Nutrient Supplementation A*t
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CONTENTS (Continued)
Page
Biologtcal Treatment Section 44
IV. MATERIALS AND METHODS 47
Experimental Systems 47
System 1 - Chemical/Physical followed by
Biological Treatment 47
System 2 - Chemical/Physical Treatment 47
System 3 - Biological followed by Chemical/
Physical Treatment 49
System 4 - Biological Treatment 49
System 5 - Bench-Scale Testing 49
Process Monitoring 50
Statistical Tests - 52
Presentation of Results 54
V. RESULTS AND DISCUSSION -- 55
Preliminary Results 55
Raw Leachate Quality 55
Lime Dosage 59
Sulfuric Acid Dosage 60
Phosphoric Acid Dosage 60
System 1 - Physical/Chemical Plus Activated Sludge 61
Operational Comments 69
Cost Data 72
Nitrification 75
Summary r ' 90
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CONTENTS (Continued)
Page
System 2 - Chemical/Physical Treatment 90
Operational Comments 95
Cost Data 95
Factors Influencing Lime Treatment Performance 95
Systems 3 and k - Biological Treatment of Raw Leachate 104
System 5 - Laboratory Studies 107
Activated Carbon 107
Additional Laboratory-Scale Studies 115
Leachate Treatment Plant Startup 125
VI . CONCLUSIONS - 132
VII. REFERENCES - - - 136
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LIST OF TABLES
Page
1 - Summary of System 1 Operation Data 6
2 - The Strength of Raw Leachates 13
3 - Effect of Solid Waste Disposal on Groundwater Quality 17
4 - Effect of Landfill Depth on Leachate Composition and
Pollutant Removal at the University of West Virginia
- 1965 - - 18
5 - Theoretical Removal of Heavy Metals During Lime
Precipitation 27
6 - Leachate Treatability as Hypothesized by Chian and Dewalle 30
7 - Precipitation and Average Monthly Temperature Data
Trenton, New Jersey 35
8 - Summary of Effluent Criteria for GROWS Sanitary Landfill
Leachate Treatment Facility 37
9 - Design Leachate Characteristics 39
10 - Periods of Operation of Leachate Treatment Systems 48
11 - Routine Laboratory Chemical Analysis 51
12 - Landfill Leachate Characteristics 57
13 - Effect of Equalization Pond on Raw Leachate Variability 58
14 - System 1 Treatment Performance after Acclimation of
Activated Sludge (August 1, 1976 - May 1, 1977 and
July 1, 1978 - August 31, 1978) 63
15 - Summary of System 1 Operation
(8/1/76 to 4/30/77 and A/1/78 to 8/31/78) 68
16 - Warm Weather Operation of System 1 70
17 - Comparison of Series and Parallel Operation of Activated
Sludge Units- - 71
18 - Operation and Maintenance Costs Incurred During the
Operation of System 1 following Acclimation of Activated
Sludge (8/1/76 to 5/1/77 and 7/1/78 to 8/31/78) 73
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LIST OF TABLES (Continued)
Page
19 - Ammonia Removal In Activated Sludge Units------"-»- 78
20 - Summary of System 2 Results 91
21 - Summary of Effects of Chemical/Physical Treatment 93
22 - Summary of Operation and Maintenance Costs During
Evaluation of System 2 (11/15/75-5/1/77 and 11/1/77-
8/31/78) 96
23 - Summary of Operational Data for Lime Treatment and
Clarification 97
2k - Results of Batch Draw-and-FI11 Activated Sludge
Experiments to Determine the Extent of Phosphorus
Limitation 106
25 - System 3 Operation 108
26 - System 4 Operation 109
27 - Summary of System 3 Operation Data (5/1/77-8/31/77) 110
28 - Summary of Results of Carbon Adsorption Treatment of Raw
Leachate 112
29 - Treatment of Final Effluent with Bench-Scale Activated
Carbon Columns 113
30 - Pilot-Scale Carbon Treatment of Final Effluent 114
31 - Results of Alkaline Chlorination Studies 118
32 - Experimental Protocol and Preliminary Results in
Evaluation of Lime Treatment Additives 120
33 - Results of Additive Evaluation - - - 121
34 - Preliminary Filtration Results 124
35 - Process Loading Rates and Concentrations Observed During
the Period April 1, 1978 through June 30, 1978 129
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LIST OF FIGURES
Page
1 - Reduction in COD During Aerobic Treatment 24
2 - Changes in Total Dissolved Solids (TDS) During Aerobic
Treatment Studies 25
3 - Location of Leachate Treatment Plant 3^
k - Schematic Flow System 1 with Ammonia Stripping Lagoon k]
5 - Schematic of Pilot Leachate Treatment Plant
(Scaled Version of System 1) 53
6 - Raw Leachate Chemical Oxygen Demand 56
7 - Flow Chart for Activated Sludge in Series 67
8 - Effect of Temperature on Specific Oxidation Rate 82
9 - Substrate Inhibition of Nitrification 85
10 - Effect of Low Concentrations of Substrate on Specific
Oxidation Rate (R-) 87
11 - Effect of pH on Clarifier Effluent Nickel Concentration 101
12 - Effect of pH on Clarifier Effluent Mercury Concentration-- 102
13 - Effect of Leachate Temperature on Clarifier Effluent
Nickel Concentration 103
]k - Carbon Breakthrough Curve 116
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DEMONSTRATING LEACHATE TREATMENT
Report on a Full-Scale Operating Plant
R.L. Steiner, Ph.D., P.E., J.D. Keenan, Ph.D.,
A.A. Fungaroli, Ph.D., P.E.
Summary and Conclusions
The results of 3 years of operation of a full-scale sanitary
landfill leachate treatment plant are reported. The plant is designed
to provide a variety of chemical/physical and biological treatment
sequence options. The chemical/physical units include equalization,
lime precipitation, sedimentation, air stripping, neutralization and
nutrient supplementation. These treatment processes are designed to
remove heavy metals, ammonia and organic materials, and to encourage
subsequent biological treatment by reducing the pH and adding the
nutrient phosphorus. The biological treatment process is activated
sludge designed to provide both organic 5-day biochemical oxygen
demand (BOD_) degradation and nitrification. The demonstration
leachate treatment plant is designed to provide operational flexibility
in that the flow can be directed through the various unit processes and
operations in any sequence.
The purpose of this project was to demonstrate the efficiency of a
number of treatment sequences. Specifically, five modes of operation
were defined and have been investigated. System 1 consists of chemical/
physical treatment followed by activated sludge; System 2, chemical/
-1-
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physical treatment only; System 3, biological treatment followed by
chemical/physical; System 4, biological treatment only; and, System 5,
bench-scale studies, including activated carbon adsorption treatment.
Data have been collected which can be used to characterize the
quality of raw leachate generated in an operating sanitary landfill.
These data show that the leachate from this sanitary landfill source
is high in organic matter (average chemical oxygen demand (COD)/liter
of 18,553 mg, average BOD^/liter of 10,907 mg) and nitrogen (average
NH^-N/liter of 1,001 mg). At the end of the first 2 years of operation
these figures were 11,210 and 17,562; 4,460 and 10,773; and 1,503 and
1,047, respectively. Thus, although influent nitrogen values have
fallen, the increase in organic strength has been extremely large. The
raw leachate heavy metal concentrations are somewhat lower than
expected, possibly reflecting the relatively high pH of the leachate.
(Note that all data have been collected with nonfiltered samples.)
High concentrations of ammonia in the raw leachate exceed the
plant's effluent criterion and are sufficient to inhibit the growth of
the activated sludge microorganisms. For this reason the original
plant design was augmented with an ammonia stripping lagoon.
System 5 studies have been conducted for a number of purposes.
Bench-scale tests have provided optimal operating data for chemical/
physical units. In particular, System 5 has provided data for the
f
development of lime, sulfuric acid, and phosphoric acid dosages.
Activated carbon adsorption has been evaluated as a treatment
method for raw leachate. For raw leachate, carbon adsorption did not
prove to be an effective treatment procedure. The inability to use
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carbon adsorption is the result of high suspended solids loading causing
pore plugging and the wide range of flow variability.
Pilot scale data have been collected for System 5, carbon
adsorption of System 1 effluent. In this mode, the carbon column would
serve as a tertiary, or advanced waste, treatment process. The results
indicate that the carbon can remove much of the remaining COD and heavy
metals. The results have been analyzed in terms of Langmuir adsorption
isotherms and carbon breakthrough curves. This way of handling the data
provides preliminary full-scale design information.
Systems 3 and k, those in which raw leachate is influent to the
biological units, have received considerable operating attention. The
results indicate that the raw leachate is not directly treatable by
biological means. Systems 3 and k yield an effluent which is high in
organic matter. The mean effluent BOD from System 3 was 763 mg per
liter. The performance of Systems 3 and A has not been satisfactory
for the treatment of this leachate.
Systems 1 and 2 are those in which the raw leachate is treated
first by chemical and physical means. The results of these systems
are most promising. During the third year, these systems were preceded
by equalization. Lime precipitation followed by sedimentation has been
successful in removing the heavy metals and a portion of the organic
matter. Specifically, this sequence (System 2) has removed about one-
quarter of the nitrogen; one-third of the dissolved solids; one-half
of the organic matter; three-quarters of the suspended solids; and
ninety percent of the phosphates. The sequence has been successful in
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removing the heavy metals including one-half of the cadmium and
mercury; two-thirds of the lead, chromium, and nickel; three-quarters
of the copper; over ninety percent of the iron and zinc.
The performance of System 2 has been studied carefully in order to
determine the treatment unit's response to a number of operational
parameters. It was found that temperature and pH both exert an effect
on the concentration of heavy metals in the lime treatment effluent.
However, the response is not identical for all heavy metals. It may be
possible to use the differences in these responses in an operational
control strategy to achieve optimal removal efficiences of selected
contaminants.
An ammonia stripping lagoon is included in the chemical/physical
treatment sequence because of the excessive ammonia levels in the raw
leachate. During the lime precipitation/clarification/ammonia stripping
mode of operation, the following removal efficiencies have been achieved:
66 and 50 percent of the BOD and COD, respectively; approximately 60
percent of the ammonia-N and total Kjeldahl-N; approximately 75 percent
of the suspended solids; 25 percent of copper; 50 to 60 percent of
cadmium and nickel; 6k to 68 percent of lead; approximately 96 percent
of zinc; 98 percent of iron.
The ammonia lagoon has a detention time of 1.7^ days, thereby
providing an equalizing effect. That is, the effect of the lagoon is
to dampen the peaks and to minimize shock loadings on subsequent
treatment units. For example, during the period in which the lagoon
was included in the treatment sequence, the mean ammonia concentration
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in the raw leachate was 1001 mg per liter with a standard deviation
slightly larger, indicating tremendous variability. During the same
period, the t] standard deviation interval for the ammonia lagoon
effluent was 203 to 6^1 mg per liter. Thus, the equalization effect is
significantly beneficial in terms of lessening shock loadings.
During the third year, an equalization pond was used to further
dampen the fluctuations in leachate quality and quantity. This was
done to provide a more even flow to the lime treatment unit. The
effect of the equalization was to reduce influent variability for many
parameters, as measured by the coefficient of variation; and to enable
more uniform dosing of raw leachate with lime.
System 1 provided the best degree of treatment. This sequence
consists of equalization, lime precipitation/clarification/ammonia
stripping/neutralization/phosphorus addition/activated sludge. In this
operational configuration, excellent removal efficiencies have been
observed, following the adaptation of the activated sludge to the waste
(Table 1). Except for NH.-N, BOD,., and lead, the effluent concentrations
comply with the criteria developed by the Pennsylvania Department of
Environmental Resources and the Delaware River Basin Commission for
discharge to the Delaware River. The standards for these parameters
were not met because of the unusually severe temperatures of the winter
of 1976-77, and secondarily because of the great increase in raw
leachate strength which began during the second year of this project.
(The treatment performance of System 1 met all standards during periods
with relatively warm weather. During the period up to January 1977
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TABLE 1
SUMMARY OF SYSTEM 1 OPERATION DATA
Parameter
Ammon ia-N
BOD
Cadmium
Chromium
COD
Copper
1 ron
Lead
Mercury
Nickel
Zinc
8/1/76
Raw
Leachate
mc/1 iter
758
11886
0.08
0.26
18*490
0.1*0
333
0.7^
0.006
1.76
19.5
to 5/1/77 and 4/1/78 to 8/31/78
Final Discharge
Effluent Percent Standard
mq/liter Removal mq/Uter
75
153
0.017
0.07
9^5
0.11
2.7
0.12
0.00*»
0.75
0.53
90.1
98.7
78.2
73-1
9^.9
72.5
99.2
83.8
27.4
57.^
97-3
35
100
0.02
0.1
5V
0.2
7.0
0.1
0.01
a.
0.6
No discharge standard for this parameter.
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System 1 consistently met the effluent criteria. Likewise, during
the third project year, the summertime performance of System 1 was
excel lent.)
The System 1 operating data have been examined closely in order to
characterize the ammonia removal mechanisms. In the lagoon this occurs
as the result of volatilization of the free ammonia predominant at high
pH levels. In the activated sludge units, the principal mechanism for
ammonia removal is biological nitrification to nitrate. The rate of
nitrification, expressed as the specific oxidation rate, is a function
of temperature which follows the van't-Hoff Arrhenius relationship.
The results show that the activation energy is approximately 12350 cal.
9 ~1
per mole, and the Arrhenius frequency factor is 2.18 x 10 day
The data indicate that substrate inhibition due to ammonium ion
concentration occurs in this system. This relationship has been fitted
to the Haldane inhibition model. The maximum specific oxidation rate
is 3.5 g N oxidized per g biomass/day. The saturation constant is A
mg per liter, and the inhibition constant is 36 mg per liter.
-7-
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DEMONSTRATING LEACHATE TREATMENT
Report on a Full-Scale Operating Plant
R.L. Steiner, J.D. Keenan, and A.A. Fungaroli
I. INTRODUCTION
The potential for water pollution from sanitary landfill sites has
become recognized in recent years. A number of studies have documented
the great pollutional strength of landfill leachates. The quality
of this material varies with landfill age, nature and moisture content
of the wastes disposed at the site, and hydrologic and soil factors.
In spite of this variability, it can be stated that, especially for
young landfills, the values of the critical sanitary parameters of
leachate are at least an order of magnitude greater than for domestic
sewage. The deleterious consequences following contamination of ground
and/or surface waters by leachate may be severe, and it is for this
reason that leachate treatment is receiving attention.
Solid waste consists of matter which can be decomposed by bacterial
or microbial action, as well as of materials which are inert to
microbiological activity. Some of the compounds, cellulose in
particular, are resistant to biological breakdown, but with sufficient
time decomposition will occur. Because of this resistivity and
necessity to acclimate the biological system, the chemical characteristics
of leachate are time-dependent. To complicate treatment, as the paper
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decomposes, some of the Inorganic ions which are bound to the organic
matrix are released and can be removed by water percolating through
the landfill. The actual mechanism of removal varies with the component
but includes solution as well as colloidal transport.
The generation of leachate in landfills is complicated and cannot
be generalized simply as surface water percolating through the sanitary
landfill. When refuse is placed in the landfill, decomposition begins
to occur. Some decomposition products may be water soluble whereas the
parent products might not have been. This is especially true of
cellulose. In addition, the inorganic constituents also must be
considered since they vary with the state of decomposition. The amount
of water percolating through a sanitary landfill is the primary control
of leachate quality, but the chemical characteristics of the leachate
are dependent on other parameters, including temperature, water
composition, moisture content, time, mode of decomposition (aerobic,
etc.) and the amount of infiltration of rainfall at the landfill.
Recent studies have shown that leachate is produced in a sanitary
landfill when the precipitation exceeds the net evapotranspiration of
the region. Remson, Fungaroli and Lawrence developed a model for
predicting the movement of leachate through a sanitary landfill.
Further results using this model have substantiated the validity of the
approach and prediction of leachate generation patterns is reasonably
accurate. Dass et al. have also used a water budget method for
predicting leachate generation.
Ground and surface waters can be protected if the landfill is
underlain with an impervious membrane. With proper design, leachate
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is then directed toward collection points. A waste such as this, which
is properly considered an industrial waste, must be treated prior to
surface discharge. The leachate treatment state-of-the-art is still
embryonic, although a few small scale studies have been conducted.
These have demonstrated that neither conventional chemical treatment
nor biological treatment can achieve the high degree of treatment
efficiency expected today. Consequently, although we know that the
pollution potential of sanitary landfill leachate can be avoided by
interception using impervious liners, we are not yet able to define
the optimum sequence of unit operations and processes required for
adequate wastewater renovation.
The U.S. Environmental Protection Agency, Office of Solid Waste,
awarded a demonstration grant (S-803926) to investigate the
effectiveness of alternative treatment sequences as employed at the
full-scale facility in Falls Township, Pennsylvania. A 380 liter
per minute (0.144 mgpd) plant had been constructed to treat leachate
from the GROWS (Geological Reclamation Operations and Waste Systems,
Inc.) landfill. This project had as its primary goal the evaluation
of the technical feasibility, operational efficiency, and cost
effectiveness of four alternative treatment sequences. These are:
(1) chemical/physical followed by biological; (2) chemical/physical
alone; (3) biological followed by chemical/physical; and (4) biological
alone. The chemical/physical processing includes precipitation of
heavy metals by lime addition, sedimentation, air stripping of ammonia,
and neutralization using sulfuric and/or phosphoric acids. Equalization
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of raw leachate was initiated during the third year of the project.
Biological treatment consists of conventional activated sludge.
Additional objectives of the study were the bench-scale evaluation of
carbon adsorption on both raw leachate and unit process effluents; and
bench-scale testing to determine chemical dosage, sludge return rates,
aeration rates, and other plant operation criteria (System 5). The
purpose of this document is to present and discuss the results of the
3 years of operation of this facility.
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II. OVERVIEW OF LEACHATE TREATMENT OPTIONS
The purpose of this chapter Is to review the literature regarding
the composition of sanitary landfill leachates and their treatment. In
brief, the character and variability of the leachate dictates the types
of treatment systems which will be effective. The contaminants of
greatest concern fall into several groups. The first group is the
organic chamicals, important primarily because they exert an oxygen
demand on receiving waters which may result in a depletion of dissolved
oxygen deleterious to aquatic life. The second major group of
contaminants found in sanitary landfill leachates is comprised of the
heavy metals. As a group, these elements are of concern because they
are toxic at sufficiently high concentrations. It is conventional
practice to chemically characterize wastewaters such as leachate in terms
of a number of other parameters. These are used for a variety of
purposes including design, operation control, and evaluation of pollution
potential.
Leachate Composition
In 1932, one of the first studies indicating that the disposal of
. solid waste could cause environmental pollution was reported by Calvert
who investigated the liquid waste from a garbage reduction plant in
2
Indianapolis. In this process the garbage was cooked and the grease
removed to produce fertilizer and animal feed, and the liquid waste was
discharged into an impounding pit or lagoon. An analysis of this liquid
is presented in Table 2, Column 1. Calvert analyzed the groundwater
from existing wells surrounding the lagoon and found that wells up to
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500 feet downstream of the site showed a marked increase in magnesium,
calcium, total dissolved solids and carbon dioxide.
Carpenter and Setter, working at New York University in 1940,
19
conducted one of the earliest studies concerned with landfill leachate.
Auger holes were drilled through an existing landfill of undetermined
age into the subsoil. Twenty-eight samples of leachate which were
collected in the bore holes were analyzed chemically. The range of
concentrations is presented in Table 2, Column 2. These results showed
a wide variation of concentration over the site, thus indicating the
difference of filled materials at various locations, or the differences
in the age of the refuse at different points. Analysis of groundwater
in the area was not performed; therefore, the effect on the subsurface
environment was undefined.
The first comprehensive research study of sanitary landfills under
controlled conditions was conducted at the University of Southern
California. Test bins, simulating landfill conditions, were constructed.
Water was added to simulate the infiltration of 1.12 m and leachate was
collected and analyzed. Table 2 gives the minimum and maximum (Column
3) values of the initial (first 45.9 liters of leachate per cu m of
compacted refuse) leachate. The most rapid removal (the highest
concentrations) occurred with the first 232 liters per cu m of refuse.
Thus, it was postulated that removal would continue for many years but
at a very slow rate, and it was considered unlikely that all the
constituents would ever be removed.
-------
The same study also examined a field site consisting of 2.k m of
refuse and 0.61 m of cover material. The refuse was in Intermittent
contact with the groundwater, analysis of which showed increases in all
organic ions and a maximum biochemical oxygen demand of 125 mg/liter.
One conclusion of the study was that the dissolved inorganic ions
entering the groundwater through intermittent contact would decrease In
concentration as a result of dilution and adsorption and travel in the
direction of the groundwater movement.
The other conclusions reached in this study are summarized as
follows: (1) A landfill, if located so that it is in intermittent or
continuous contact with ground water, will cause the ground water in the
immediate vicinity of the landfill to become grossly polluted and unfit
for domestic or irrigational use; (2) dissolved mineral matter, entering
ground water as a result of intermittent and partial contact of a
landfill with the underlying ground water will have its greatest travel
in the direction of flow, undergo a vertical diffusion to a limited
extent, and be subject to dilution, the result of which will be a
minimizing of the effect of the entering pollutant ions; (3) a landfill,
if located so that no portion of it intercepts the ground water, will
not cause impairment of the ground water for either domestic or
irrigational use; (4) rainfall alone (in the area of this study) will
not penetrate a 2.3 m thick landfill sufficiently to cause entry of
leachate Into the underlying ground water.
Longwel1 stated in 1957 that an appreciable proportion of refuse
could be extracted by water to produce a leachate rich in organic
-15-
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21
matter, Inorganic salts (ions), and bacteria. The analysis of a
surface leachate obtained from an unnamed landfill is given in Table
2 (Column *f).
In 1961 the British Ministry of Housing and Local Government
conducted extensive research on the placement of landfills above the
groundwater table (which they called "dry tipping"), and the placement
of landfills below the groundwater table (which they called "wet
22
tipping"). In the "wet tipped" experiment the refuse was completely
submerged and the horizontal groundwater flow rate was equivalent to
138 liters per sq m per day. The leachate quality is included in Table
2 (Column 5). Analyses of the groundwater before and after contact with
the refuse are given in Table 3- These results show the considerable
extent of groundwater quality degradation due to pollution by leachate.
In 1965, Qasim studied the seepage waters from simulated landfills
23
at the University of West Virginia. Three concrete cylinders 0.9 m in
diameter and 1.2, 2.A and 3.7 m in height were filled with municipal
refuse. Approximately 102 cm of precipitation were artificially added
to the cylinders over a period of 6 months and leachate samples were
collected. The maximum concentrations of certain organic and inorganic
components in the leachate from the three cylinders are presented in
Table k. Table k also presents the total weight removed per cubic
meter from each depth of fill by 102 cm of simulated infiltration.
A summary of results presented by Qasim demonstrates the effect of
depth on leachates generated by landfills. Concentrations of various
pollutants were higher in leachates obtained from deeper fills.
Concentrations of various pollutants per unit depth of fill decrease
-16-
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TABLE 3
EFFECT OF SOLID WASTE DISPOSAL ON GROUNDWATER QUALITY-
GROUNDWATER QUALITY BEFORE AND AFTER INTRODUCTION
OF "WET TIPPED" LANDFILL - 196126
Concentration (mg/liter)
Measured Quantity
Total Solids (Residue)
Chloride
Alkal inity, as CaCO,
Sulfate
Biochemical Oxygen Demand (BODc)
Organic Nitrogen
upstream or
Landfill
1*50
30
180
120
0
0
Downstream ot
Landfill
5,000
500
800
1,300
2,500
70
-17-
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-18-
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with increasing depths of refuse. For an equal amount of influent,
shallower fills showed greater extraction rate per unit volume of fill
than deeper fills. The bulk of the pollution was attributed to initial
leaching.
Anderson and Dornbush conducted an extensive investigation of the
27
groundwater leaving a landfill in Brookings, South Dakota in 1967.
An abandoned gravel pit of 160 acres with its base well below the
water table was filled with municipal solid waste. The purpose of the
investigation was to determine which chemical parameters were the most
reliable indicators of the influence of landfills on the groundwater.
Groundwater samples from 22 wells located over the site were analyzed
for chloride, total hardness, alkalinity, sodium, pH, potassium, iron,
nitrate, and specific conductance. A considerable increase in all
constituents measured was observed in three wells immediately downstream
of the fill area. Although the authors did not evaluate the potential
pollution of municipal refuse, they did report an increase of up to
50 times the chloride content of native waters in the groundwater
affected by the leachate. The major conclusion of this investigation
was that two of the most important indicators of pollution from
landfills are chlorides and specific conductance or total dissolved
solids. Chloride ions are easily detectable, not readily absorbed by
soils, not affected by biological processes, and apparently an abundant
product of leachates.
Disposal sites in northern Illinois were investigated in 1970 by
28
Hughes et_ aj_. Leachate samples from three landfills of varying age
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were obtained as near to the base of the refuse layer as possible. The
results of these analyses are presented in Table 2 (Columns 6-8).
Although no Information is given in the study as to the composition of
the solid waste in each fill, and the analyses were performed on only one
sample, the results do show a decreasing trend with time. However, It
was noted that refuse more than 15 years of age can still have a high
total dissolved solids contentindicating that the stabilization of
landfills is a long process.
The laboratory simulated landfill or lysimeter study conducted at
Drexel University from 196? to 1972 is the only study reported that was
conducted under completely controlled laboratory conditions. It was
also the only study reported in which the environmental conditions
completely simulate the existing climatic conditions of a region, In
this case, southeastern Pennsylvania. The refuse was placed at as
received moisture content and allowed to reach field capacity naturally
through the addition of amounts of distilled water equal to the
precipitation of the area nrnus the evapotranspiration. This
infiltration was added on a weekly basis and varied from a rate of 8.9
cm per month during the wet periods to zero during the dry or summer
periods. Approximately one year was required for the refuse to reach
field capacity, but small quantities of leachate were generated before
field capacity was reached. The maximum concentrations obtained in the
first year are given in Table 2, Column 9.
It was concluded that this initial leachate production came from
the following sources: (l) From the refuse. Most of the initially
generated leachate is squeezed from the organic components of the refuse
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by the compaction and placement procedure. (2) From channeling. Some
of the water added at the top of the lysimeter may find a direct route
through the refuse to the collection trough, due to any inhomogeneities
in the refuse. (3) From an advanced wetting front. The wetting front
in the refuse probably moves as a broad band rather than as a single
line interface. As a result, substantial increases in leachate will
occur before the entire system is at field capacity, (k) From the main
wetting front. This is the leachate which is produced when the system
reaches field capacity. At this time, the input water and the output
leachate quantities become approximately equal.
Other studies have mentioned the leachate problem of refuse
disposal in papers dealing with other aspects of the solid waste problem.
Leo Weaver has stated that municipal refuse can generate leachates high
in organic pollutants. Data from this study are included in Table
2 (column 10).
Engineering Science in a study conducted in 1967 in southern
California concluded that groundwater pollution, which may arise from
refuse leachate reaching a water source, will be shown largely as an
32
increase in total dissolved solids and specific conductance.
Walker in 1969 found that a sand and gravel aquifer in Illinois
was -ineffective in removing dissolved chemical ions generated by a
landfill. He did report that travel of leachate through a short
distance (3 to 5 m) of this aquifer will remove organic pollutants
generated by landfills in Illinois and concluded by stating that
inorganic pollutants constitute the greatest source of concern.
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Roessler noted an increase in inorganic pollutants in an industrial
water supply 2i miles downstream from a refuse dump 10 years after the
34
dump had started operation.
Table 2 (columns 11 to 13) presents a summary of values of raw
leachate composition as compiled by Chian and DeWalle.^5 The ranges
represent leachates examined by a number of investigators (Range 1
Column II) and a variety of leachates studied at the University of
Illinois (Range 2Column 12). These data are the results of a recently
completed literature review. Another recent report summarizes the
state-of-the-art with respect to ground water monitoring for leachate
contamination. This paper should be consulted before initiating a
monitoring program.
The conclusion to be drawn from this review of landfill leachate
quality (as summarized in Table 2) is that its composition is highly
variable from site to site. In addition, the data show that even at
a given landfill, considerable variation is encountered with respect
to both space and age. That is, variability is a factor within a
landfill and also over the history of the site. Consequently, it is
concluded that landfill leachate quality cannot be predicted a priori;
and that this quality is even variable at a given site.
Leachate Treatment
Leachate treatment system? have been evaluated on a laboratory
scale at Drexel University. In one study, the purpose was to
characterize the biodegradation of organic matter both with and without
37
the supplementary addition of chemicals. The system consisted of
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five aerobic units which were treated in the following manner:
(1) control-no treatment; (2) addition of sodium hydroxide to pH 9;
(3) addition of sodium hydroxide to pH 11; (4) addition of lime;
(5) addition of lime plus sodium carbonate. Otherwise, all units were
handled in the same manner. This procedure included preparation of an
activated sludge culture by aerating leachate. Each experimental unit
was seeded with this culture and was aerated at a rate of 3k liters of
air per gram chemical oxygen demand (COD) (1500 cu ft per Ib COD).
During the testing, all settled solids were recycled to the aeration
tank with no sludge wastage. The aeration treatment systems were
operated on a continuous basis with a hydraulic residence time of
five days.
The COD values decrease quite rapidly during the first six days
and thereafter approach a limit (Figure l). The results indicate that
there are components of leachate which are not amenable to treatment
in an aerobic system. The time of adaptation of microorganisms for
treatment of the organic fraction of leachate may be considerably longer
than normal sewage. Volatile solids concentrations in these tests were
low when compared to normal activated sludge systems. This may be one
reason for the long time required for stabilization.
A high variation in the concentration of total dissolved solids
in the treated effluent was noted (Figure 2). The cyclic variation of
several systems is of interest, but not all of the systems show this
phenomenon. Since the withdrawal and addition of leachate was constant,
there was no reason for the cyclic effect. Only pretreatment with lime
-23-
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