United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-86/073 Mar. 1987
&EPA Project Summary
Critical Review and
Summary of Leachate and
Gas Production from Landfills
Frederick G. Pohland and Stephen R. Harper
A Cooperative Agreement between the
Municipal Environmental Research Labora-
tory and Georgia Institute of Technology
was established in 1983 to provide an
evaluation of the state-of-the-art in
municipal waste, landfill leachate and gas
management. Accordingly, summaries of
full-scale and experimental-scale data on
leachate and gas characteristics, control
methods, and the performance of a num-
ber of biological and physical-chemical
treatment alternatives have been devel-
oped and are presented together with
recommendations for process implemen-
tation and future research.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH, to
announce key findings of the research pro-
ject that is fully documented in a separate
report of the same title (see Project Report
ordering information at back).
Introduction
In the United States, sanitary landfills
are the most frequently employed method
for disposal of solid waste. Unfortunately,
sanitary landfills remain poorly understood
and are often loosely managed. During the
last decade, the problem of leachate and
gas in landfills received major attention,
particularly in terms of environmental con-
sequences associated with their migration
during conversion of waste constituents.
These concerns led to a variety of devel-
opments for control, including the con-
cepts of leachate containment and total
landfill isolation. Various techniques have
been proposed and implemented for the
treatment and disposal of landfill gases
and leachates.
The purpose of this project was to pro-
vide a review and summary of the nature
of leachate and gas production at landfills,
and to couple this with a concomitant in-
ventory of available techniques for con-
tainment, control and treatment. The
review begins with a brief historical per-
spective of hazards associated with the
migration of leachate and gas from land-
fill disposal sites. Factors affecting the
quantity and quality of landfill leachate
and gas are then addressed, followed by
processes used or advocated for leachate
and gas treatment. Hence, investigations
into activated sludge, aerated lagoons,
trickling filters, biodisks, anaerobic contact
processes and in situ leachate recycle
technologies as well as coagulation, pre-
cipitation, chemical oxidation, disinfection,
adsorption, ion exchange, and reverse
osmosis processes in either separate or
combined configurations are detailed.
Finally, methods for the ultimate disposal
of leachate and gas are addressed, in-
cluding discharge to municipal wastewater
treatment plants, land application, and
energy recovery.
General Conclusions
The development of rational and eco-
nomically sound solutions to landfill leach-
ate and gas migration hazards encompass-
es the analysis of several major factors. A
given landfill in its natural setting will af-
fect and be affected by numerous hydro-
logic and geologic circumstances that
must be properly recognized and managed
to minimize human and environmental
risks. In particular, leachate and gases
formed as a consequence of external
moisture inputs and waste degradation
may migrate into the surrounding environ-
ment, contaminate drinking water sup-
plies, and create other environmental
hazards.
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Logically, effective management of gas
and leachates at susceptible landfill sites
begins with containment; i.e., installation
of "impermeable" barriers augmented by
sufficient drainage, venting, and collection
systems to handle the inevitable produc-
tion of leachate and gas. Following their
generation and capture, leachate and gas
must be treated and disposed of in an
environmentally and economically sound
manner.
As shown in Figure 1, a number of op-
tions are available for leachate and gas
management prior to ultimate disposal.
Before discharge onto land or into a pub-
licly owned treatment works (POTW),
landfill leachate and gas require treatment
by biological and/or physical-chemical
methods, some of which are successful-
ly proven, while others have limited appli-
cability. Moreover, it is widely recognized
that the quantity and quality of landfill
leachate and gas are influenced by numer-
ous variables, resulting in a diversity of
relative treatment efficiencies. Some gen-
eralizations on the advantages and disad-
vantages of these processes are outlined
in the remainder of this section of the
project summary.
Leachate Treatment and Process
Performance
When considering external treatment of
raw leachate for removal of biodegradable
contaminant fractions, biological treat-
ment systems are significantly superior to
physical-chemical techniques, as indicated
in the performance summary in Table 1. If
given sufficient residence time (9C), bio-
logical processes typically achieved up to
99% organics (BOD5 and COO) removal
and yielded effluents having COD concen-
trations less than 500 mg/1. Generally,
the aerobic treatment processes were ca-
pable of 90% NH3-N conversion and
yielded effluents containing less than 10
mg/l NH3-N for 0C >10 days. Also, for 0C
of 6 to 10 days, the limiting range for
aerobic carbonaceous material conversion,
60% to 80% nitrification was generally
achieved.
Like the aerobic biological processes,
anaerobic biological processes have been
successfully applied for treatment of raw
leachates. Typically, COD and BOD5 re-
movals of 90% were achieved at residence
times longer than 10 days and gas produc-
tion from anaerobic processes ranged from
0.4 to 0.6 m3/kg COD or 0.8 to 0.9 m3/kg
BOD5 destroyed.
Aerobic biological processes were fairly
efficiently applied to removal of heavy
metals. Removal efficiencies were best
with zinc, iron, cadmium and manganese;
followed by chromium, lead and nickel.
Zinc, chromium, and iron were removed at
efficiencies greater than 90% during an-
aerobic treatment; copper, lead, cadmium,
and nickel removals were on the order of
50% to 90%. Removals of alkaline earth
metals were relatively unaffected by eithei
aerobic or anaerobic processes, although
the literature reports that the activated
sludge process has removed 64% to 99%
calcium.
Direct Use
Pipeline
Flaring
Potential
Fire Hazards
Drinking Water
Contamination
Municipal
and
Industrial
Waste
0.0
200 400 600
Stabilization Time, Days
External Treatment
Biological Treatment Physical/Chemical Treatment
Activated Sludge
Aerated Lagoon
Stabilization Pond
Fixed-Film Processes
Anaerobic Filter
Anaerobic Contact
Precipitation/Coagulation
Chemical Oxidation
Disinfection
Adsorption
Ion Exchange
Reverse Osmosis
Combined Treatment
Figure 1.
T I
P.O.T.W. = Discharge Options = Land Application
Treatment options available for leachate and gas management and ultimai
disposal.
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Table 1.
Summary of Leachate Treatment Process Capabilities
Aerobic Biological
Processes
Activated Sludge
Combined Leachate
and Sewage
Aerated Lagoon
Stabilization Pond
Aerobic Fixed Film*
Rem.,
95
94-99
99
93-99
BOD5
Effl.,
mg/l
100
3-15
5-60
10-1OO
Rem.,
95
92-98
92-98
99
COD
Effl.,
mg/l
500
25-60
300-800
100-4OO
Rem.,
%
70-95
-
40-70
70-99
TKN
Effl.,
mg/l
10- 100
-
" 40-80
4-100
Rem.,
96-99
-
99
80-99
Fe
Effl.,
mg/l
10-40
-
0.2
1-100
Zn Ni
Rem., Effl., Rem., Effl., Comments
% mg/l % mg/l
96-99 3-10 60 0.25 0C = 6-10 days
- - - - ratio <5%
- - - - 0C>70 days
— - - — T >40 days
Anaerobic Biological
Processes
Attached Growth 85-98 100-900 75-95 200-1000
Suspended Growth 85-98 100-900 75-95 200-1000
Leachate Recycle NA <100 NA <5
NA
20-1000
80-99 5-25 80-99 0.5-10 10-80
80-99 5-25 80-99 0.5-10 10-80
NA 5-50 NA 0.2-1 NA
0.1-1 Qc>10days
0.1-1 Qc >5 days
- 9C >500 days
Physical/Chemical
Processes
Coagulation —
Oxidation —
Reverse Osmosis -
Ion Exchange -
Adsorption —
12 100-10,000
10-50
60-90' • 10OO-8000 -
86-94 <10
40-70 100-300
75-99 <10
95-99 2-17 75-98 <1 - - Lime, alum.
ferric chloride
99 <1 90 <1 - — Ozone, chloride
permanganate
— — — — — — — Raw Leachate
Pretreated
Leachate
40-80 1-10 20-96 <1 14-96 <1 Commercial IX
Resins and GG
- 65-95 2-15 - - - - GAC and PAC
Rem. = Removal; Effl. = Effluent.
'Insufficient data to make an adequate judgment;
"TOC Basis.
Generally, with the exception of acti-
vated carbon, the physical-chemical proc-
esses were unsuccessful in removal of
organic materials from raw leachates.
However, reverse osmosis, activated car-
bon 95% TOC removal «100
mg/l effluent) with a maximum asdsorp-
tive capacity of 200 mg TOC/g AC.
In situ treatment of leachate using
leachate containment and recycling back
through the landfill waste mass was suc-
cessful. Pilot- and full-scale demonstration
of effluents from leachate recycle studies
were typically 30 to 350 mg/l BOD5, 70
to 500 mg/l COD, 4 to 40 mg/l iron and
<1 mg/l zinc. Also, the implementation of
leachate recycling generally reduced the
time required for biological stabilization of
the readily biologically degradable leachate
constituents by as much as an order of
magnitude. Whereas wastes in landfills
without leachate recirculation may require
15 to 20 years to stabilize, leachate recy-
cle may shorten this period to 2 to 3 years.
Moreover, if removal and ultimate disposal
of accumulated leachate are followed by
appropriate capping and maintenance of
closed landfill sections, the potential for
long-term adverse environmental impacts
will be greatly diminished by concomitant
removal of refractory substances remain-
ing in the stabilized leachate, while also
depriving the system of that liquid (leach-
ate) transport medium. Even though the
ultimate reactivity or fate of refractory
compounds within landfills have not been
well established, leachate recycle appears
to offer a management option for reduc-
ing the degree of uncertainty and providing
a better basis for predicting ultimate
behavior.
Gas Treatment Process
Performance
Effective recovery of energy (methane)
from landfills requires appropriate provi-
sions for gas collection and treatment,
perferably prior to initiation of the landfill
operations. Collection and treatment sys-
tems must be sized according to expected
gas rates and yields. The literature indi-
cates that the 0.005 m3 to 0.10 m3 of
total gas are produced per kilogram of dry
refuse placed. Most of the total gas is pro-
duced over a relatively short period dur-
ing the life of a landfill; most of the
methane is produced within a few years
after the onset of rapid stabilization and
methanogenesis. Accordingly, typical gas
production rates reported in the literature
range from 0.001 to 0.008 m3/kg of dry
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refuse/year. These rates may be increased
with recycle-augmented stabilization due
to the shortened period (months versus
years) for accelerated conversion of the
readily available biodegradable materials
present in the refuse leachate. The associ-
ated gas composition ranges from 45% to
60% methane; the balance is primarily
carbon dioxide with smaller amounts of
hydrogen, oxygen, nitrogen and traces of
other gases.
The choice of treatment technologies
for purifying recovered landfill gas de-
pends on the intended use of the product.
For high BTU pipeline quality gas, treat-
ment traditionally included the removal of
water, carbon dioxide, hydrogen sulfide,
hydrocarbons and, on occasion, nitrogen.
For on-site applications, lesser degrees of
treatment have been commonly required
to remove water and hydrogen sulfide;
however carbon dioxide, hydrocarbons and
nitrogen are not necessarily removed.
Water removal may be best effected by
either adsorption or absorption; absorption
with ethylene glycol at <20°F «6.7°C)
is the method of choice. Non-methane
hydrocarbons are removed using carbon
adsorption. Carbon dioxide is removed by
organic solvents, alkaline salt solutions, or
alkanolamines. Hydrogen sulfide is re-
moved along with C02 by the above
methods, or it may be selectively removed
by particular absorbents or adsorbents.
Because many of the solvent processes
exhibit a higher affinity for H2S than for
C02, these two gases may be removed
concurrently. Dry oxidation processes
(such as iron sponges) are more specific
for hydrogen sulfide, although the non-
regenerative nature of the support mate-
rials (such as wood shavings) often poses
a requirement for additional recharging
procedures. Nitrogen is removed by lique-
fying the methane fraction of landfill gas,
although this is energy intensive, under-
scoring the need to avoid introducing air
during extraction from the landfill.
General Recommendations
The generation and treatment of land-
fill leachate and gas are influenced by a
number of factors, many of which are
poorly understood and ineffectively con-
trolled or managed. Collectively, these
issues have been emphasized by the re-
sults of studies reviewed in this report.
Associated uncertainties tend to stymie
management efforts and, as a result, the
design, construction and operation of ex-
ternal leachate treatment facilities have
not been standardized. Similarly, efforts
directed toward energy (methane) re-
covery have been limited because of the
difficulties in predicting variations in gas
quality and production, as well as secur-
ing justification for such an initiative within
the user community.
To help alleviate such problems during
design and operation of leachate and gas
management systems, generation of
leachate and gas must be controlled so as
to transfer the process from the realm of
uncertainty to that of predictability. This
can be accomplished only if control over
leachate constituents is exercised either
through the pre-selection of waste source
ingredients or by management of their rate
of generation and transfer to the transport
medium (leachate or gas). The latter ap-
proach appears to be a more logical choice
in the case of municipal landfills; the
former, perhaps coupled with the latter,
would seem more attractive for industrial
landfills.
Based upon an understanding of the
processes effecting leachate characteris-
tics, management of generation and trans-
fer rates can be implemented by control
of the moisture regime within the landfill.
Without moisture, the transport medium
will not exist and the conversions and in-
teractions determining leachate (and gas)
quality will be suppressed. Once under
control, the availability of moisture can be
used to advantage to accelerate processes
producing teachable constituents, to carry
the constituents from the waste mass, to
dilute out inhibitory ingredients and/or
refractory compounds, to add seed, nut-
rients or buffer capacity to augment bio-
logical activity, and to transport residuals
for ultimate treatment or disposal.
Implicit in this management concept are
requirements for containment and ultimate
disposal. Current technology provides a
sufficiency of techniques for containment
with natural or fabricated liners which
have become generally accepted. Ultimate
disposal relates to the sensitivity of the
eventual environmental receptor, whether
it be the land or the water. However, under
prevailing regulatory constraints and state-
of-the-art technology, both require some
degree of leachate pretreatment before
ultimate disposal is acceptable. It is the
premise here that such pretreatment can
be best provided in engineered systems
that have the resiliency to cope with
changing leachate characteristics.
In situ Treatment of Leachates
For on-site applications, it is recom-
mended that leachate recycle be recog-
nized as affording the flexibility needed to
successfully manage landfill leachates,
both with respect to leachate quality and
quantity and energy recovery. Associated
design of leachate and gas collection and
distribution systems should be standard-
ized and coupled with management plans
allowing sequenced operation of the land-
fill and reuse of appurtenances to minimize
overall costs and maximize the benefits of
such treatment. Current evidence suggest-
ing lower costs of leachate recycle in con-
tained sites as compared to either sepa-
rate aerobic or anaerobic treatment sys-
tems should be confirmed. In addition,
since with leachate recycle the landfill
itself provides the treatment system,
operational contingencies should be estab-
lished in relation to the accelerated pro-
duction of leachate constituents and their
eventual conversion to gas.
Whether leachate values are attractive
for recovery and/or reuse also relates to
the type of treatment provided. At many
conventional municipal landfills, gross
uncertainties persist throughout operation
and after closure of the site. Accordingly,
gas and leachate production events are
generally unpredicatable and neither gas
nor leachate may be efficiently recovered
for controlled discharge. With leachate
recycle and its inherent ability to acceler-
ate waste and leachate conversion with
concomitant methane production, gas col-
lection and possible utilization becomes
more viable and such an option should be
investigated further, particularly on full-
scale. Moreover, the degree of stabilization
of the waste mass as compared to con-
ventional landfill practice needs to be
established with regard to residual leach-
ate character and decisions on ultimate
leachate disposal including foreclosure
and postclosure requirements.
External Treatment of Leachates
and Gas
In the case of external treatment of
leachates, the most logical first step ap-
pears to be biological treatment. Stabiliza-
tion ponds or aerated lagoons can be most
cost effective if land area is readily avail-
able; if not, anaerobic treatment or aerobic
activated sludge processes may be used.
The choice between anaerobic and aerobic
processes for leachate treatment is a dif-
ficult one, although the retention times
needed in either case are similar. There-
fore, the energy surplus associated with
methane production and aerator elimin-
ation may favor anaerobic processes. Both
processes require further site specific
testing on pilot- and full-scale to determine
these issues. In particular, these systems
will require attention to the flexibility in
design and operation necessary to meel
the challenges imposed by the stochastic
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nature of leachates (and gas) in both qua-
lity and quantity.
Following external biological treatment
(or in situ treatment, as above), the efflu-
ents will still contain significant organic
and inorganic residual concentrations.
Therefore, polishing treatment prior to
disposal on land or into a POTW such as
by activated carbon adsorption, ion ex-
change or reverse osmosis needs to be in-
cluded in the overall study approach. Pre-
cipitation and coagulation processes
should also be considered where justified.
In all cases, gas management or recovery
need to be an integral part of any invest-
igative initiative.
Directions for Future Research
Based upon the observations gained
from this review, the present state-of-the-
art in landfill leachate and gas manage-
ment appears to be comprised of the ele-
ments represented in Figure 2. From this
figure, it is suggested that 90 to 95% of
the organics and metals leached from
landfill waste may be removed by biolog-
ical processes such as leachate recycle or
external aerobic and anaerobic treatment
systems. However, the capabilities of
these processes are not fully established;
further study is needed in each area to
develop meaningful economic and realistic
process control comparisons of these
alternatives. Evaluations of leachate treat-
ment and the gas production possible from
the use of leachate recycle on full-scale are
particularly needed, as well as parallel
evaluations of both aerobic and anaerobic
fixed-film processes on pilot- and full-
scale, respectively. The sequence ap-
proach to leachate recycle on full-scale
needs development to establish the eco-
nomic incentives associated with minimiz-
ing leachate distribution and gas collection
appurtenances and maximizing gas/
recovery utilization. In all biological treat-
ment cases, the stochastic nature of
leachate and gas production in both
quantity and quality needs to be merged
with design and operational procedures.
Activated carbon, ion exchange or re-
verse osmosis polishing of effluents from
biological treatment processes need fur-
ther confirmation on full-scale. Included in
these analyses should be a characteriza-
tion of organics and inorganics escaping
treatment, and the potential for improving
final polishing by chemical pretreatment or
posttreatment. Coupled with this initiative
should be more detailed analyses of the
character and fate of the priority pollutants
appearing throughout the various phases
of landfill stabilization and/or in situ or
separate treatment.
Medium-Btu (Direct Use)
High-Btu (Pipeline)
—4 *-
CO2 fr H2S __£,. VOC
Refnoval ^Removal Removal Removal *" Removal
Gas Treatment
MUJ
NlCIPAL AND INDUSTRIAL WASTE
Combined
Treatment
In Situ
vs.
External
Treatment
Leachate
Recycle
(Leachate + Sewage)
Leachate/vVastewater ratio <5%
90-95% Organic
and Metal Removal
A
Aerobic or Anaerobic
Biological
Treatment
90-95% Organic
and Metal Removal
'on Exchange
Adsorption
C/)e/n/ca/ Oxidation
Precipitation/ Coagulation
T
Physical-
Chemical
Treatment
95-99% Organic
and Metal Removal
Discharge
toP.O.T.W.
Land Application
f t) .A
Figure 2. Solutions to the management of leachate and gas from landfill disposal of solid
wastes.
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Finally, the present state-of-the-art of
leachate and gas management from land-
fills fails to provide a unified approach to
leachate and gas treatment and possible
resource recovery. Particularly lacking is
the recognition of factors influencing
leachate and gas formation and an integra-
tion of these factors for optimization of
design and operational strategies in order
to improve overall acceptance of this
waste management technology. There-
fore, complementary research and/or dem-
onstration studies should be directed
toward such a goal with the eventual
development of standardized management
and control procedures for all types of
landfills.
Frederick G. Pohland and Stephen R. Harper are with Georgia Institute of
Technology, Atlanta. GA 30332.
Steve James is the EPA Project Officer (see below).
The complete report, entitled "Critical Review and Summary of Leachate and Gas
Production from Landfills," (Order No. PB 86-24O 181'/AS; Cost: $16.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
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
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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