&EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/137 September 1993
Project Summary
Behavior and Assimilation of
Organic and Inorganic Priority
Pollutants Codisposed with
Municipal Refuse
Frederick G. Pohland, Wendall H. Cross, Joseph P. Gould, and Debra R. Reinhart
Research was undertaken to demon-
strate and evaluate the capacity of land-
fill systems to assimilate and attenuate
inorganic and organic priority pollut-
ants loadings codisposed with munici-
pal refuse and to determine the fate
and effect of the codisposed pollutants
as landfill stabilization progressed un-
der conditions of single-pass leaching
and leachate recycle.
The results from the study of 10 simu-
lated landfill columns demonstrated that
the columns employing leachate recycle
achieved waste stabilization more rap-
idly and completely and exhibited
greater assimilation and attenuation of
the codisposed priority pollutants than
did the single-pass columns.
This Project Summary was developed
by EPA's Risk Reduction Engineering
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
Effective management of increasing
amounts of solid waste has become a
priority societal challenge. Of all available
solid waste management options, disposal
in landfills is most frequently employed,
primarily because of associated economic
advantages and tradition. Moreover, re-
gardless of the emphasis on other solid
waste management alternatives, the land
will continue to serve as a final waste
receptor, whether for combustion ash, dis-
cards from recycling initiatives, or regu-
lated hazardous waste.
Landfills are currently designed and op-
erated to minimize potential nuisances and
adverse health and environmental impacts
by controlling disposal methods and by
managing leachate and gas generation.
One of two fundamental leachate man-
agement strategies can be employed; one
strives to limit rainfall infiltration and pro-
vides single-pass leaching with leachate
collection, removal, and separate treat-
ment before ultimate discharge; the sec-
ond involves controlled rainfall infiltration,
leachate collection, and in situ recircula-
tion or recycle before ultimate discharge.
"The former strategy is characteristic of the
more conventional or traditional ap-
proaches, whereas the latter leachate re-
circulation technique is a more recent in-
novation that essentially converts the land-
fill into a controlled anaerobic bioreactor
with accelerated waste conversion and sta-
bilization in a more predictable and cost-
effective manner. In either case, the gases
generated from waste stabilization consist
primarily of methane and carbon dioxide,
but greater opportunities for controlled en-
ergy recovery and use of the methane are
afforded when the temporal and spatial
dimensions of .landfill development are
planned to regulate the progress of waste
stabilization. Therefore, accelerated stabi-
lization can result from in situ leachate
recirculation in controlled landfills, with
enhanced opportunities for recovery and
use gas as a useful energy source.
Because most landfills essentially exist
as anaerobic biological waste stabilization
processes during most of their active lives,
the same fundamentals that apply to sepa-
rate anaerobic treatment processes also
Printed on Recycled Paper
-------
apply to landfills, although effective reten-
tion times and opportunities for use and
conversion of less available substrates in
these separate treatment systems are dif-
ferent from those provided by the landfills
of today. Therefore, the purpose of this
research was to employ this analogy to
demonstrate the comparative capacities
of both single-pass leaching and leachate
recycle for waste stabilization and con-
comitant assimilation and attenuation of
both organic and inorganic priority pollut-
ants when codisposed with municipal
refuse in simulated landfills.
Construction, Loading, and
Operation of the Simulated
Landfills
The construction and operational fea-
tures of the five pairs of simulated landfills
with single-pass leaching and with leachate
recycle are illustrated in Figure 1. All five
pairs received equal quantities of shred-
ded municipal refuse, with one pair serv-
ing as controls and the other column pairs
receiving organic and inorganic priority
pollutants at the test loadings indicated in
Table 1. The corresponding combined
loadings to each of the simulated landfills
are indicated in Table 2. After loading,
moisture was added incrementally to the
simulated landfills to initiate leaching and
waste stabilization; an average of 350 L
for the recycle columns and 1430 L for
the single-pass column over the 1428-day
operational period. The moisture added to
the former recycle columns was restricted
to the amount necessary to maintain
leachate recirculation, whereas that added
to the latter single-pass columns was
equivalent to local rainfall infiltration rates
averaged over the experimental period.
The initial moisture additions were made
intentionally to establish and prolong the
acid formation phase of landfill stabiliza-
tion until the effects of aggressive leachate
generation could be ascertained. Thereaf-
ter, incremental anaerobic digester sludge
(a total of 111 L) and pH neutralization
(Na2COp) were added over a 232-day pe-
riod to induce methane fermentation. On
completion of the methane fermentation
phase, the simulated landfill operations
were ended and the columns were disas- j
sembled for inspection and retrieval of j
waste matrix samples for analysis.
Presentation and Discussion of
Results
Leachate samples from each of the 10
simulated landfill columns were routinely
collected and analyzed for pH, total and
individual volatile acids, alkalinity, COD,
TOC, ORP, chloride, ammonia, nitrogen,
sulfate, sulfide, Na, K, -
Ca, Mg, Fe, Cd, Cr, Pb, Mn, Ni, Hg,
and the organic priority pollutants or their
conversion products. Similarly, gas
samples from each column were analyzed
for C02, O2, N2, H2, and CH4, and for the
volatile organic priority pollutants or their
conversion products. Ambient temperature
throughout the experimental period (10.3°C
to 31.1°C) were also recorded.
Selected results for cumulative gas pro-
duction (Figure 2) and its composition
(Table 3), leachate pH (Figure 3), and
total volatile acids (Figure 4) indicate the
dramatic differences between performance
1 Gas meter
2 Temperature readout
3 Pressure gauge
4 Ball valve
5 LeachateAvater distributor
6 Shredded municipal refuse
7 Silicone sealed bolted joint
8 Check valve
9 Recycle pump
10 In-line strainer
11 Gravel underdrain
12 Thermistor
13 30 mil HOPE lining
14 Gravel
Recycled simulated landfill column
Single-pass simulated landfill column
Figure 1. Construction and operational features of simulated landfills.
-------
Table 1. Simulated Landfill Column Loadings and Operation
Column Column,
number identity Operation
1 CR Recycle
2 CS Single-Pass
3 OS Single-Pass
4 OLS Single-Pass
5 QMS Single-Pass
6 OR Recycle
7 OLR Recycle
8 OHS Single-Pass
9 OMR Recycle
. 10 OHR Recycle
* CR Control, Recycle
CS Control, Single-Pass
OS Organics, Single-Pass
OLS Organics, Low Inorganics, Single-Pass
QMS Organics, Medium Inorganics, Single-Pass
OR Organics, Recycle
OLR Organics, Low Inorganics, Recycle
OHS Organics, High Inorganics, Single-Pass
OMR Organics, Medium Inorganics, Recycle
OHR Organics, High Inorganics, Recycle
Organics
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Inorganics
No
No
No
Low
Medium
No
Low
High
Medium
High
,
with leachate recycle and single-pass
leaching, the discrete separation of peri-
ods of active acid formation and methane
fermentation (~ day 800), and the com-
parative effects of the organic and inor-
ganic priority pollutant loadings. Elevated
total volatile acids (TVA) concentrations
and low pH and gas production were in-
dicative of the acid formation phase of
landfill stabilization, whereas reduced TVA
concentrations and elevated gas produc-
tion and pH were indicative of the meth-
ane fermentation phase. Moreover, more
gas resulted from leachate recycle opera-
tions, where convertible substrate was re-
tained within the landfill columns, than re-
sulted from the single-pass leaching op-
erations, where substrate was washed out
and wasted with an equivalent loss in
potential gas (and energy) yield. Similarly,
the recycle columns were less affected by
the priority pollutant loadings, with retar-
dation of stabilization more related to heavy
metal loadings than to organic priority pol-
lutant additions.
The differences in the effects of priority
pollutants were determined to be a func-
tion of sufficiency and intensity of poten-
tial attenuating mechanisms. For example,
the reducing conditions prevailing during
methane fermentation provided a favor-
able chemical environment for microbially
mediated reduction of sulfates to sulfides
and the resultant removal of many of the
heavy metals as sparingly soluble sulfides,
as exemplified by leachate cadmium re-
ductions (Figure 5); or for reductive
dehalogenation as exemplified by leachate
dibromomethane (Figure 6); or trichloroet-
hylene (Figure 7) reductions with accumu-
lations of conversion products (Br and vi-
nyl chloride), respectively. The magnitude
of conversion was greater with leachate
recycle than with single-pass leaching,
largely because of the enhanced opportu-
nities for microbial acclimation with the
extended contact times (~ 350 days) of
the former as contrasted with the greater
inhibition and washout effects of the lat-
ter.
In the final analysis, in addition to the
more efficient and accelerated waste sta-
bilization provided by leachate recycle in
contrast to single-pass leaching, the in
situ conversion and transformation of the
organic and inorganic priority pollutants
was more rapid and complete. Although
varying quantities of the organic priority
Table 2. Shredded Municipal Refuse, Organic and Inorganic Priority Pollutants, and Sawdust Loadings (in g) for Each Simulated Landfill Column
Column number and type*
Constituent
1CR 2CS
30S
40LS
50MS 60R
70LR
80HS
90MR
* C = Control, R = Recycle, O = Organic pollutants,,
+ As placed refuse, in kg.
= Low metals, M = Medium metals, H = High metals, S = Single-pass.
100HR
Trichloroethene — —
Dibromomethane — —
2-Nitrophenol — —
1 ,4-Dichlorobenzene — —
Nitrobenzene — —
Naphthalene " — —
1 ,2,4-Trlchlorobenzene — —
2,4-Dichlorophenol — —
Hexachlorobenzene — —
Lindane — —
Bis-2-ethylhexylphthalate — —
Dieldrin — —
Cadmium — —
Chromium — —
Mercury — —
Nickel — —
Lead — —
Zinc — —
Sawdust 6,000 6,000
Shredded Municipal Refuse+, kg 381 381
120
120
120
120
120
120
120
120
120
120
30
30
'.
6,000
381
120
120
120
120
120
120
120
120
120
120
120
30
35
45
20
75
105
135
6,000
381
12.0
120
120
120
120
120
120
120
120
120
120
SO
70
90
40
150
210
270
6,000
381 ,
120
120
120
120
120
120
120
120
120
120
120
30
—
—
—
—
—
—
6,000
381
120
120
120
120
120
120
120
120
120
120
120
30
35
45
20
75
105
135
6,000
381
120
120
120
120
120
120
120
120
120
120
120
30
140
180
80
300
420
540
6,000
381
120
120
120
120
120
120
120
120
120
120
120
30
70
90
40
150
210
270
6,000
381
120
120
120
120
120
120
120
120
120
120
120
30
140
180
80
300
420
540
6,000
381
-------
1CR
60R
-#- 70LR
-9- 90MR
100HR
200 400
600 800 1000
Time Since Loading (Days)
1200
1400
70
60
SO
rf 40
30
20
10
200
400
600 800 1000
Time sinca loading (days)
1200
Figure 2. Cumulative gas production during simulated landfill investigations.
1600
1400 1600
pollutants were leached, retained, or trans-
formed (Tables 4 and 5), most of the
inorganic heavy metals were either wasted
with the discarded leachate (single-pass
columns) during acid formation, or re-
moved mainly by precipitation and matrix
capture during methane fermentation. In-
deed, little of the original heavy metal
loadings was detected in the leachates
from any columns at the end of the ex-
perimental period, with the recycle col-
umns serving as effective reservoirs for
capture and storage of the heavy metals.
Summary and Conclusions
Ten simulated landfill columns were op-
erated in pairs with either single-pass
leaching or leachate recycle through or-
ganic and inorganic priority pollutants that
had been codisposed with shredded mu-
nicipal refuse. The results demonstrated
that the fate and effect of the codisposed
priority pollutants and the progress of land-
fill stabilization were affected by the
leachate management and loading tech-
nique employed. The columns employing
leachate recycle achieved waste stabiliza-
tion more rapidly and completely, as evi-
denced by trends in gas and leachate
characteristics, and also exhibited greater
assimilation and attenuation of the
codisposed priority pollutants than did the
single-pass columns. Furthermore, al-
though the overall gas production and qual-
ity was reduced in the columns receiving
loadings of inorganic and/or organic prior-
ity pollutants, these loading effects were
more severe for the single-pass than for
the leachate recycle columns.
Conservative leachate constituents, such
as chloride and sodium, could be used to
reflect the effects of single-pass or leachate
recycle operations. Although these con-
stituents were retained within the leachate
of the recycle columns at relatively con-
stant concentrations, they were removed
from the single- pass columns primarily by
washout. This washout from the single-
pass columns served to reduce leachate
concentration profiles and lessened op-
portunities for complete waste stabiliza-
tion and/or effective assimilation/attenua-
tion of priority pollutant loadings. Opera-
tions with leachate recycle did not inhibit
stabilization of the readily degradable
waste fractions, although some retarda-
tion was evident at higher priority pollut-
ant loadings; results with single-pass leach-
ing did, however, inhibit both waste stabi-
lization and attenuation processes, mainly
because of washout of essential nutrients
and elimination of potential in situ attenu-
ating mechanisms. These microbially me-
diated mechanisms were expressed for
the leachate recycle columns principally
by abiotic and biotic transformation and
sorption of the organic priority pollutants
within the waste matrix, or by precipita-
tion, sorption, ion-exchange, filtration, and
matrix capture of the inorganic priority pol-
lutants. Therefore, results of these investi-
gations have firmly established the effi-
cacy of controlled landfill systems with
leachate containment, collection, and re-
cycle for accelerated in situ stabilization of
both nonhazardous and hazardous solid
waste constituents.
-------
Table 3. Comparison of Gas Composition Composition During Simulated Landfill Investigations
Column
identity
Project
day
when N2
becomes
small
(<5%)
Project
day
when CH4
appears
(>1%)
Average gas percentage
during the
methane fermentation phase
(project days 910-1428)
C02 N2 CH4
Recycle:
1CR
6OR
7OLR
9OMR
10OHR
Single-pass:
826
868
854
868
868
700
742
728
728
714
44.02
45.17
46.07
45.42
43.54
2.77
0.67
0.71
0.61
0.95
52.81
54.14
53.20
53.96
55.44
2CS
3OS
4OLS
5OMS
8OHS
896 238
700
714
714
700
45.37
42.96
39.47
38.21
45.81
0.79
21.95
31.23
37.74
18.88
53.74
34.3$
28.73
23.77
34.26-
Based on the extensive database de-
veloped during the course of the investi-
gations, it could be concluded that:
1. Controlled leachate containment,
collection, and recirculation offers
opportunities for more rapid and
complete stabilization of landfilled
municipal solid wastes, including at-
tenuation of codisposed organic and
inorganic priority pollutants, than
does the single-pass leaching more
commonly associated with tradi-
tional landfill practices.
2. Loadings of codisposed priority pol-
lutants in the form of heavy metals
3.
and/or selected classes of toxic or-
ganic substances can retard the se-
quential phases of landfill stabiliza-
tion. Loading effects will, however,
more severely affect leachate and
gas characteristics during single-
pass leaching than during leachate
recycle operations.
Leachate and gas characteristics,
described by various physical and
chemical indicator parameters, can
be used to reflect the progress of
waste conversion in terms of lon-
gevity and intensity of the acid for-
mation and methane fermentation
phases of landfill stabilization.
4. A threshold inhibition level for waste
conversion, equivalent to the high-
est inorganic priority pollutant load-
ing, was established with leachate
recycle operations, whereas with
single-pass leaching, inhibition was
exhibited at the lowest priority pol-
lutant loading. When extrapolated
to practice, however, these effects
would be a function of site-specific
conditions, including the waste load-
ing and operational techniques em-
ployed.
5. Landfills possess a finite capacity
to attenuate hazardous and
nonhazard-ous organic and inor-
ganic waste constituents through a
wide array of biological and physi-
cochemical mechanisms, these
mechanisms principally include re-
duction, pre-cipitation, and matrix
capture for heavy metals, and bi-
otic or abiotic transformation with
matrix interaction through sorption
for organic priority pollutants.
6. Controlled landfill systems, de-
signed and operated as anaerobic
bioreactors with leachate contain-
ment, collection, and recycle, en-
hance predictability and opportuni-
ties for effective management,
thereby minimizing potential ad-
verse health and environmental ef-
fects, while encouraging innovation
and associated regulatory and pub-
lic acceptance.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR-
812158 by Georgia Institute of Technol-
ogy under the sponsorship of the U.S.
Environmental Protection Agency.
-------
« 5
- I
200 400
1CR
600 800 7000
77/779 since loading (days)
7200 7400 7600
Recycle column
6OR -36- 7OLR
9OMR
10OHR
iS
I'
% 5
I
_L
I
_L
I
200 400
600 flOO 7000
77me since loading (days)
7200 7400 7600
2CS
Single pass column
3OS -^- 4OLS -\
5OMS
8OHS
Figure 3. Leachate pH during simulated landfill investigations.
-------
200 400 600 flOO WOO
Time since loading (days)
1CR
1200
60R
Recycle column
7OLR -E
9OMR
1400
1600
10OHR
200 400 600 800 1000
Time since loading (days)
1200
1400
1600
2CS
SOS
Recycle column
4OLS -B- 5OMS
8OHS
Figure 4. Leachate total volatile acids during simulated landfill investigations.
-------
10O
80
60
<3 40
20
i /I N
AY It
Recycle
column
-m- tCR
—I- 6OR
-*- 70LR
9OMR
200 400
600 800 1000
Time since loading (days)
1200 1400 1600
100
200 400
600 800 1000
Tirna since loading (days)
1200 1400 1600
Figure 5. Leachate cadmium during simulated landfill investigations.
-------
200
1
or
§ 750
€
o
J 100
Q
50
0
*
- r-
- f
- li
I/ O
I 3\,
Jf jftl?
V*l
^TitaLrf
Recycle
column
— h 6Ofl
-*- 7OZ.R
200 400
600 SOO 1000
Time since loading (days)
1200
1400 1600
250
200
S
of
150
50
0
0
4
' /
•/
/
'/
/
•
f\
N
Single-pass
column
-a- 2CS
— 1- SOS
-*- 40LS
-H- 5OMS
"A" 8OHS
i'i
1 i
M i
TI A.
vJ *•
200 400
600 soo rooo
77/ne s/nce loading (days)
1200
1400 1600
Figure 6. Leachate dibromomethane during simulated landfill investigations.
-------
200
400
600 SOO 7000
Time since loading (days)
1200
1400
1600
I
801
70
60
40
30
20
10
0
0
200 400 600 800 1000
Time since loading (days)
1200
1400
1600
Figure 7. Leachata trichloroethylene during simulated landfill investigations.
10
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Table 4. Mass Balance Summary on Organic Priority Pollutants for the Single-Pass Simulated Landfill
Columns, Percent
Compound
Leached
Retained
Transformed *
Dibromomethane (DBM)
Trichloroethene (TCE)
Nitrobenzene (NB)
2-Nitrophenol (NP)
2,4-Dichlorophenol (DCP)
1,4-Dichlorobenzene (DCB)
Naphthalene (NAP)
Lindane (UN)
1 ,2,4-Trlchhrobenzene (TCB)
Dieldrin (DIEL)
Hexachlorobenzene (HCB)
Bis(2-ethylhexyl)phthalate (BEHP)
14.1
(6.1-27.4)"
10.7
(7.77-14.58)
0.75
(0.02-2.31)
0.31
(0.03-1.16)
10.9
(8.66-11.81)
3.8
(2.53-5.98)
1.2
(1.04-1.34)
0
0.17
(0.08-0.32)
0
0
0
0
0
0
0
15.4
(0.74-25.2)
48.4
(30.96-68.63)
46.8
(17.48-59.53)
52.2
(0-100)
39.7
(6.67-60.0)
0
57.1
(0-96.67)
0
85.9
(72.6-93.9)
89.3
(85.42-92.23)
99.25
(97.69-99.98)
99.69
(98.84-99.97)
73.6
(57.71-137.75)
47.8
(28.55-81.27)
52.0
(39.13-81.27)
47.8
(0-100)
60.1
(42.00-93.01)
100
42.9
(3.33-100)
100
"Ranges in parentheses.
tMass not accounted for in the teachate or recovered from the waste.
Table 5. Mass Balance Summary on Organic Priority Pollutants for the Recycle Simulated
Landfill Columns, Percent
Compound
Leached
Retained
Transformed t
Dibromomethane (DBM)
Trichloroethene (TCE)
Nitrobenzene (NB)
2-Nitrophenol (NP)
2,4-Dichlorophenol (DCP)
1,4-Dichlorobenzene (DCB)
Naphthalene (NAP)
Lindane (LIN)
1,2,4-Trichlorobenzene(TCB)
Dieldrin (DIEL)
Hexachlorobenzene (HCB)
Bis(2-ethylhexyl)phthalate(BEHP)
1.71
(0.12-2.66)*
0.57
(0.40-0.83)
0.07
(0.02-0.10)
0.03
(0.01-0.04)
2.55
(0.41-8.73)
1.20
(0.21-3.90)
0.41
(0.09-1.32)
0
0.05
(0.0-0.17)
0
0
0
0
0
0
0
25.17
(6.50-41.99)
35.37
(18.99-48.89)
48.28
(21.75-63.31)
66.29
(33.75-93.17)
38.15
(32.58-43.75)
0
86.31
(46.42-100)
0
98.29
(97.34-99.88)
99.43
(99.04-99.60)
99.93
(99.90-99.98)
99.97
(99.96-99,99)
72.29
(41.99-94.39)
63.44
(50.79-80,80)
53.00
(21.2-78.16)
33.71
(6.83-66.25)
61.81
(37.42-67.40)
100
13.69
(0.53.58)
100
Ranges in parentheses.
*Mass not accounted for in the leachate or recovered from the waste.
11
•frll.S. GOVERNMENT PRINTING OFFICE: 1993 - 75O-O7I/80085
-------
F.G. Pohlandls with the University of Pittsburgh, Pittsburgh, PA 15261; W.H. Cross and
J.P. Gould are with the Georgia Institute of Technology, Atlanta, GA 30332, andD.R.
Reinhartis with the University of Central Florida, Orlando, FL 32816.
Roberts. Landreth is the EPA Project Officer (see below).
The complete report, entitled "Behavior and Assimilation of Organic and Inorganic
Prbrity Pollutants Codisposed with Municipal Refuse," (Order No. PB93-
222198AS; Cost: $36.50, 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/137
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