United States
Environmental Protection
Agency
Risk Reduction Engineering
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/064 Feb. 1990
&EPA Project Summary
Treatment of Hazardous Landfill
Leachates and Contaminated
Groundwater
Robert C. Ahlert and David S. Kosson
The objective of this study was to
assess pilot- and field-scale
application of separate or combined
biological and physical/chemical
treatment to high-strength hazardous
dump site or landfill leachates,
extracted sludges and wastes, and
land-spilled hazardous substances.
Four types of real-world toxic,
concentrated, complex wastes served
as prototype waste streams:
industrial landfill leachate, leachate
from an industrial sludge Impound-
ment, forced extract from impounded
industrial sludge, and groundwater
contaminated with a chlorinated
solvent Techniques evaluated during
bench- and laboratory-scale experi-
ments were: dispersed and fixed-film
aerobic and anaerobic mixed
mlcroblal systems, flocculation/pre-
cipitation, ultrafiltratlon (UF), and
reverse osmosis (RO). In general,
some physical/chemical pretreatment
(liming, floe/settle) was required to
obtain high efficiency biodegrada-
tion. The biodegradation effluent
could be "polished- by UF, RO, or ion
exchange when required to meet
National Pollutant Discharge Elimina-
tion System (NPDES) standards. Soil-
based field pilot plants were
constructed and operated to dem-
onstrate sequential aerobic/an-
aerobic mlcrobial treatment for
leachates from two CERCLA-NPL
sites and for groundwater contam-
inated with 1,1,1-trichloroethane
(TCA) at a third site. Even in the
presence of high concentrations of
inorganic salts, organic carbon
reductions of 95% to 99% were
achieved. The levels of chlorinated
solvents extracted In subsurface
waters were reduced from 5 mg/L to
less than 20 pg/L (greater than
99.6%). The contaminant reductions
attained are not the maximum that
could be achieved but reflect
pragmatic, cost effective treatment
levels.
This Project Summary was devel-
oped 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
The major objective of this study was
to demonstrate pilot- and field-scale
treatability of high-strength dump or
landfill leachates, extracted sludges or
wastes, and land-spilled hazardous
substances. Two specific treatment types
were examined: biological treatment and
physical/chemical treatment.
Biological investigations involved
dispersed and fixed-film mixed and
indigenous cultures for treating
representative concentrated hazardous
aqueous wastes that could contain both
organic and inorganic compounds. The
need for sequential process steps was
recognized. At the outset, only bench-
scale methodologies were undertaken.
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Various sources of microbial seed were
used, and evidence for long-term
adaptations and responses were
considered of primary importance.
Experiments were designed to fill a gap
in existing literature that focuses on
degradation of single hazardous species
and binary or very simple multiple
solutes in solution with water. Studies of
complex—mixed organic and inorganic-
solute systems have not been reported.
Physical/chemical treatment of influent
to and effluent from bioreactors was
identified as important, but was given a
lower priority since it is less novel.
Potential physical/chemical treatments
included: RO, UF, flocculation/sedi-
mentation, membrane separations, and
adsorption. As with biological treatment,
feed streams were mixed solutions of
multiple organic species and heavy
metals in water. Emphasis was placed on
high-strength and complex solutions and
on the need to inactivate or detoxify toxic
metal species, as well as biogenic,
biodegradable, and refractory organic
compounds. Investigations of biological
treatment techniques were marked by
two concerns: (1) product water quality
suitable for discharge to the environment,
and (2) minimum volume and maximum
strength of concentrated residues for
ease of handling and/or recovery.
During the program, microbial
treatment for four types of high-strength,
complex aqueous wastewaters was
investigated. These included: industrial
landfill leachate, leachate from an
industrial sludge impoundment, forced
extract from impounded industrial sludge,
and groundwater contaminated with
chlorinated solvent. Pretreatment by
physical/chemical methods was soon
shown to be essential to remove colloids
and fouling agents. Ultimately, total
organic carbon (TOC) reductions of 95%
to 99% were achieved, even in the
presence of high concentrations of
inorganic salts. Acclimated, mixed
microbial populations were employed in
all cases; no genetically engineered or
specifically cultured organisms were
used. Aerobic and anaerobic regimes
were developed, in sequence, in packed-
bed (soil-based) bioreactors.
Biological treatment was evaluated in
bench-scale experiments with laboratory
column reactors. Much common ground
was discovered with respect to organic
carbon loading rates, nutrient require-
ments, buffering, and co-substrates for
co-metabolism. Design criteria for scaled-
up investigations were derived.
The laboratory column work pro-
gressed so well that resources were
available to treat three additional
hazardous waste liquors treated in pilot
plants designed specifically for the
purpose. Out-of-door, pilot-scale treat-
ment of landfill leachate was first
demonstrated in a pilot unit at the
University. Subsequently, sludge extract
solution and chlorinated solvent solution
were treated in field-site pilot plants built
and operated at the actual sites of
contamination. In these cases, field
performance matched or exceeded
bioreactor performance in the laboratory.
In conjunction with Enviresponse, Inc., a
conceptual design for a transportable,
mixed microbial, hazardous organic
solute treatment system was developed.
In short, the ability to treat complex,
organic waste solutions has been
demonstrated in the field and is available
for application to numerous CERCLA
sites.
Physical/chemical treatment is gener-
ally necessary for pre- and post-
biological reactor processing. Unit
processes of this type are required for
separation of dispersed oil and particulate
matter and for quantitative reductions in
heavy metal and inorganic salt
concentrations. Through membrane
separations and selective adsorption, it is
possible to reduce solute concentrations
to levels compatible with direct discharge
of treated effluent. Several process tech-
nologies in this category were
demonstrated to function very effectively
in conjunction with biological treatment.
Methods, Discussion, and
Results
Leachate Characteristics
For the initial phases of this work,
leachate was obtained from a large
commercial landfill receiving substantial
quantities of industrial wastes. Leachate
emanating from this landfill is collected in
open basins or lagoons and allowed to
settle by gravity. A floating oily layer is
removed and stored in drums. The
underflow from the collection basin is
pumped to API separators for further oil
removal. Bulk oil separated by gravity
has been found to contain high
concentrations of PCBs. The bulk
aqueous phase has high residual turbidity
consisting of colloids, stable emulsions,
and fine particles coated with oil, which
must be removed by pretreatment. After
pretreatment, the clarified aqueous phase
has the following range of properties:
dissolved organic
carbon (DOC) 8,000 - 12,000 mg/L
chemical oxygen
demand (COD) 23,000 - 30,000 mg
total dissolved
solids (TDS
@ 103c C) 15,000 -17,000 mg
Other typical values include TK
ammonia-N, and sulfate at 1,450, 1,0t
and 3,400 mg/L, respectively. A lari
number of heavy metals, i.e., nickel, lee
chromium, copper, etc., are present
concentrations above 0.1 mg/L.
Later, effluent was obtained fro
natural leaching and by forced extracti
of an industrial sludge disposal lagoc
Primary and secondary sludges frc
diverse chemical manufacturing opei
tions had been impounded in the lago
for several decades. The natural leache
has the following properties:
TOC
TDS @ 103°C
TKN
170-5,000 mg
2,700 4,300 mg
25 - 820 mg
Extraction of the sludges with sodiu
hydroxide solution, at pH 10 to 1
increases these values by factors of 3
5. Trace metal concentrations a
increased also: aluminum and zinc at 1
10 mg/L, and, numerous others at 0.1
1 mg/L.
During the period of investigation,
problem of groundwater contaminati
with chlorinated solvent was suggest
for study. Concentrations of I to 15 mg
of TCA had been encountered
otherwise high-quality groundwate
Lesser concentrations of byprodu
species were also observed. Based '
environmental impacts and groundwal
quality criteria, this situation could I
defined as involving a high-streng
wastewater. A microbial remediatii
process comparable to the renovatii
processes for the very high-streng
leachates described above w,
developed, tested in the laboratory, ai
operated at pilot scale in the field.
Pretreatment
Physical/chemical pretreatment of hig
strength leachates with coag
lating/flocculating agents produces
minimal decrease in DOC, while reduci
turbidity and the level of heavy met!
present in the wastewater. Lime gave t
best results with the leachate samp
involved in this study.
Utilizing lime to a solution equilibria
pH of 12 produced greater than 98
reduction in turbidity. Reductions
dissolved TOC and COD averaged le
than 5%. Polyelectrolytes were found
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ncrease the rate but not the final level of
urbidity reduction. A pretreatment
Drotocol was developed; it included
iddition of lime in sufficient quantity,
ipproximately 6 g/L, to achieve a pH of
12 with subsequent floe settlement. The
upernatant was decanted and sparged
with C02 until the pH was reduced to 9 or
ess. At this point, the supernatant was
Jecanted and a second recarbonation
tep was used to decrease final pH to
7.5.
icrobial Treatment
Biochemical Process
Aerobic biological studies revealed that
i dispersed mixed microbial population,
icclimated to landfill leachate, degraded
30% to 90% of the organic species
Dresent in the hazardous industrial waste
iquor, with or without the addition of
glucose or other nutrients. The decrease
n DOC was not due to stripping,
evaporation, and/or sorption; it was due to
Diological oxidation. Biostabilization was
rapid. Mixed microbial cultures exhibited
a two-rate (diauxic) growth pattern (Figure
1). As signaled by the increase in pH
during the first exponential growth phase,
it is likely that the mixed culture utilizes
the fatty acid fraction of the organic
;olutes in this first phase. Further, it is
probable that at least two groups of
organisms participate in the biooxidation
process. Fatty acid metabolizing
organisms have a higher specific growth
rate than the other organisms that
contribute to the second, lower rate
portion of the growth pattern. Good
agreement in carbon balances provides
clear evidence for biodegradation of the
organic species present in the leachate.
Low sludge yield was observed in this
study; this implies a reduced sludge
problem associated with aerobic
treatment. Oxygen uptake rates, as
reflected in the volumetric flow of air-per-
reactor volume, were quite nominal. If it is
assumed that microbial maintenance
requirements are negligible, as has been
reported frequently for wastewater
systems, it is possible to quantify the role
of co-metabolism in the biological
oxidation of anthropogenic compounds.
The possibility of oxidative assimilation
(nonproliferation) is ruled out because of
the quantitative evolution of carbon
dioxide; increase in cell mass and protein
content were not measured. The ability of
the acclimated population to utilize
organic carbon and other nutrients solely
'rom the leachate further improves
.jrocess prospects. It was possible to
treat highly concentrated waste liquor,
i.e., up to 10,000 mg/L of organic carbon.
The absence of highly fluctuating DOCs
indicates a stable and well-acclimated
microbial population.
Anaerobic biological studies demon-
strated a DOC reduction of 64% for a
culture grown on leachate and a
reduction of 69% for a culture selected
for the degradation of acetate,
propionate, and butyrate. Specific DOC
utilization rates of 0.15 and 0.21 day1
were observed for the leachate and these
volatile fatty acid digesting cultures,
respectively. Cell growth was not
observed, to any significant extent, during
these batch experiments. Leachate
effects on the cultures were studied
through examination of individual volatile
fatty acids in the course of the exper-
iments (Figure 2). Large concentrations of
acetate were accumulated before overall
removal was observed. The butyrate
profile demonstrated responses similar to
that of acetate removal.
Propionate and isobutyrate were more
difficult to remove, as both left an
appreciable amount of unmetabohzed
acid. However, their concentrations were
small relative to acetate and butyrate.
Acetate and butyrate are the major fatty
acids contributing to methanogenesis.
Also, the fraction of the nonvolatile fatty
acid contaminants in the leachate that
were converted to volatile fatty acids by
the acid formers ended up primarily as
acetate, with a small fraction converted to
butyrate, propionate, and isobutyrate.
Reactor failures were encountered in
studies with 20 volume-% leachate.
These failures were probably the result of
overloading the system with volatile fatty
acids. At leachate concentrations of 5%
and 10%, no toxicity problems due to
nonvolatile fatty acids were observed.
Methane was produced at levels of 0.95
to 0.99 L/g (m3/kg) DOC removed.
The data from this study clearly
indicated that aerobic and anaerobic
biological treatment can be used in
conjunction to stabilize organic
compounds found in high-strength
hazardous waste residues.
Microbiology of Chlorinated
Hydrocarbons
This phase examined mixed anaerobic
population degradation of the haloorganic
compounds dichloromethane (DCM), l,l-
dichloroethane (DCA), and TCA. Half-kill
doses, determined from batch
experiments, defined a relative degree of
toxicity for each of the compounds. The
microorganisms exhibited great tolerance
for DCA; there was no apparent inhibition
at concentrations up to 35 mg/L.
Acclimation studies with TCA
demonstrated that continued periods of
zero gas production do not necessarily
reflect the death of the organisms.
Reactors dosed with 2 and 4 mg/L
recovered after 20 days of zero gas
production. After this lag period, daily gas
production was greater than or equal to
control reactors. The overall acclimation
period was 33 days, less than half the
acclimation period of 10 wk cited in
reports of previous work. However,
acclimation periods tend to vary greatly
for anaerobic seed cultures.
Studies with separate anaerobic popu-
lations indicated that the methanogens
were most likely responsible for degra-
dation of the chlorinated compounds
considered.
Microbial Reactor Design
Soil-based sequential aerobic/an-
aerobic microbial degradation was
investigated as a potential onsite or in-
situ treatment process. Laboratory soil
column experiments were carried out for
initial evaluation of the proposed process
using three different contaminant streams
and several soil types.
Treatment of landfill leachates
achieved reductions in DOC in excess of
90% (Figure 3). Influent leachate-derived
organic carbon (LOC) concentration,
organic carbon removal, effluent pH, and
long-term system permeability are
interrelated. Microbial acclimation periods
increased in length with increased
influent leachate concentration. In-
creasing influent LOC concentration
resulted in greater overall removal
efficiency for DOC. In addition, increased
influent LOC concentration is associated
with reduced incidence of plugging,
allowing the system to operate more
closely to target volumetric flux.
Treatment of TCA using the soil-based
microbial system, operated under
anaerobic conditions, resulted in
quantitative removal of solvent. Influent
concentrations of 20 mg/L corresponded
to effluent concentrations of less than 20
p,g/L. Failure to observe any
breakthrough phenomena, over long
periods of operation, confirmed that
sorption onto soil constituents was not
controlling TCA removal. Gas evolution
rates and gas analyses indicated that
methanogenesis was the most probable
rate-controlling step.
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.o
I
2400
2000
1600
7200
800
400
Cell Mass
DOC
2.0
1.0
0.6
IB
0.4 *
12
16
20
Time.h
Figun 1. Fate of organic carbon and microbial responses observed during a study with
20% leachate (with pH control @ 7.5 ±0.1).
Microbial Process
Demonstration
Positive results from laboratory soil
column experiments were followed by the
design, construction, and operation of
three field pilot plants to demonstrate the
process feasibility for large-scale
applications. One of the pilot plants was
located at Rutgers and the other two at
the actual sites of differing contamination
problems.
The first pilot plant in the series
consisted of six self-contained lysimeters
(bioreactor columns packed with soil), 2 ft
in diameter and 6 ft in depth. These units
were implanted in the ground, at a
location on campus, and operated in
simulation of site conditions. Pretreated
leachate from a CERCLA-NPL industrial
landfill was treated. TOO mineralization to
CO2 and CH4 was obtained with a single-
pass efficiency of 90% to 97%. Operation
was carried out for two consecutive
spring-through-fall operating periods of
approximately 160 days each. Laboratory
results were readily transferable to field
operation.
The second pilot plant was designed to
demonstrate in situ sludge extraction
coupled with soil-based microbial
treatment of recovered extract; it was
constructed and operated at the sludge
disposal site for 140 days. The cleanup
process consisted of two steps in
sequence (Figure 4). The first step was
removal of contaminants from mixed
primary and secondary industrial sludges
through in situ extraction with aqueous
sodium hydroxide. Extractant solution
was injected into the sludges throu
well-points or applied to the surfa
through a perforated pipe distribut
network. Extract was recovered by mee
of two wells screened near the bottom
the sludge deposits. The results
system operation indicated that as mi
as a 15-fold increase in removal ra
relative to natural processes driven
infiltrating rainfall, could be obtain
through controlled alkaline extraction.
additional 4-fold increase in the rate
site renovation can be obtained throi
increased hydraulic flux through I
sludges.
In this second pilot plant, extr;
recovered from the sludges was trea
to remove TOG with a soil-bas<
sequential aerobic/anaerobic microt
reactor. Treatment occurred onsi
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- 250
5% Leachate
Leachate Culture
450
500
Figure 2. Acetate and propionate concentrations as functions of batch reaction time.
immediately adjacent to the extraction
unit. A diverse, mixed microbial
population was developed in the soil
system. Neutralized extract was applied
to the surface of the treatment bed and
allowed to percolate through the soil
column. Aerobic and anaerobic microbial
populations metabolized organic con-
taminants to C02 and CH4. Treatment
efficiencies in excess of 95% were
observed.
A third pilot plant, designed to
demonstrate the treatment of
groundwater contaminated with TCA, was
operated at the site of a solvent spill. This
pilot plant consisted of two self-contained
lysimeters, 3 ft in diameter and 6 ft in
depth. The soil packing employed was
excavated from the site. Influent to the
two lysimeters was contaminated ground-
water, recovered from a monitor well, with
TCA concentrations of 5 to 20 mg/L.
Reactors were operated under entirely
anaerobic conditions. At steady state,
effluent TCA concentrations were less
than 20 u.g/L.
Sorption and Extraction
Sorption and extraction are processes
that influence the distribution of solutes
between separate phases. The absolute
performance of these processes is
dictated by thermodynamic equilibria.
Thus, the ultimate distribution of a solute
between otherwise homogeneous phases
(steady state in batch contact
circumstances) is that at which the
chemical potential of the solute is the
same in the several phases. As used in
this study, sorption is the exchange of
dissolved organic solutes between
aqueous solutions and a variety of solid
substances. The direction of exchange is
dictated by thermodynamic considera-
tions, and the rate is influenced by
physical transport and the strength of
binding forces. Extraction is the removal
of constituents from a solid phase by
contact with solvent. Distribution and rate
are controlled by thermodynamic
equilibria and, also, by physical barriers
to exchange.
Granular Activated Carbon
The time required to approach
thermodynamic equilibrium must be
determined experimentally for each
carbon (GAC) and organic solute system
combination. In general, greater than
95% of equilibrium sorptive capacity is
attained in several days. However, it may
take much longer periods to reach final
equilibrium because of slow diffusion in
carbon particle pores and/or slow
changes in surface binding states.
Pretreatment with lime to remove oily
phases from otherwise aqueous leachate
was necessary before the determination
of carbon sorption isotherms. Interactions
of GAC with leachate were independent
of the primary pretreatment process.
Control of pH through recarbonation with
C02, air stripping, or sulfuric acid
addition had little or no detectable effect
on subsequent sorption of organic solutes
onto GAC. The treatability of two leachate
samples (EPA #01 and EPA #02) with
GAC was identical.
The relationship between equilibrium
organic sorbate loading and equilibrium
solute concentrations, in multiple solute
systems, is dependent on initial
conditions. Type A isotherms were
obtained for full-strength leachate and
varying masses of GAC. Type Bn
isotherms were constructed with a
constant mass of GAC; the subscript "n"
represents the ratio of carbon-m ass-to-
volume of full-strength leachate. Finally,
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4500
4000
3500-
3000-
2500.
O
0 2000
7500-
7000-
500.
Influent
fffluent
I
20
720
740
SO 700
Time, days
Figure 3. Typical influent and effluent responses for sequential aerobic/anaerobic soil-based microbial treatment.
160
180
Type C isotherms used data for a fixed
mass of GAC and varying leachate
dilutions. With this conceptual separation
of driving forces for sorption, it was
possible to construct a mechanistic
description for the process within classes
(types). Plots of equilibrium loading
versus equilibrium concentrations of TOC
for these three types of isotherms can be
used for leachate sample character-
ization.
There is a weak pH effect on sorptive
capacities of GAC for TOC in leachate. It
appears desirable to carry out measure-
ments and treatment at near-neutral pH
rather than at higher pH levels.
Soil
Soil is an active sorbent because of
organic matter (humic) and clay fractions.
These fractions interact with organic
solutes in groundwater and infiltrating
surface water to exchange organic
substances and dissolved inorganic
species. Thus, the presence of organic
contaminants in groundwater and soil
water infers the distribution of these
substances in stable or transient
equilibria. As an example of the role of
the organic carbon fraction, the mass of
2,4-dichlorophenol sorbed onto a loam
containing 4.7% organic matter has been
observed to be approximately 5 times
greater than the mass sorbed onto a
sandy loam containing 0.84% organic
matter.
The sorption of a series of phenolic
compounds onto a loam increases in the
order:
phenol < o-chlorophenol < 2,4-
dichlorophenol.
This order is preserved for the sorption of
these solutes onto cupric and calcium
salts of commercially available humic
acid, which is a primary component of
soil organic matter.
The mass of TCA sorbed onto a loam
containing 4.7% organic matter was
observed to be 2.5 times greater than tli
mass sorbed onto a sandy clay loai
containing l.4% organic matter. In th
presence of a mixed solvent (10 volum
% ethanol), the mass of TCA sorbed onl
a loam decreased by 40%, as compare
to the single solute in aqueous solution.
Solvent Extractions
The presence of components of
landfill leachate solute matrix altered th
distribution of phenol and o-chlorophem
between a bulk organic phase and th
aqueous wastewater phase. Th
alteration was more pronounced i
experiments involving phenol than i
experiments in which o-chlorophenol wa
the distributed solute. Since phen<
favors the aqueous phase, it i
reasonable to expect solute-sa
interactions in the aqueous phase t
produce a larger change in th
distribution of phenol than in th
distribution of o-chlorophenol, whic
favors the organic phase. Th
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To
NaOH Prep.
pH 10-13
(Tank 1)
Extract
Ballast
Tank
(Tank 2)
////
Extraction Bed
Effluent
Ballast
Tank
(Tank 4)
Discharge
Figure 4. Pilot plant process flow diagram.
Soil
Treatment Bed
flQJt
Hflft
Nutrients
COi
Mixing Tank
(Tank 3)
components of a leachate solute matrix
that contribute most to the salting-out of
phenol appear to be the larger inorganic
anions, i.e., C03-2 and S04-2. High
concentrations of acetic, propionic, and
butyric acids in leachate also contribute
to observed changes in phenol as a result
of solute-salt interactions in the aqueous
or bulk organic phases.
Membrane Separations
Thin semi-permeable films become
important in the separation of dissolved
species, especially from aqueous
solution. Membranes have been used for
the production of process water and/or
drinking water from sea water and natural
brines. In addition, membranes have
been adopted for commercial separations
and concentration of products and
valuable process constituents such as
catalysts and recyclable intermediates.
Membrane techniques have a role to play
high-strength wastewater renovation.
Reverse Osmosis
Several hazardous wastewaters, e.g.,
industrial landfill leachates, lagoon
wastes, pesticide wastewaters, and
synthetic organic manufacturing effluent
were successfully renovated with an RO
system Moderate and high-strength
industrial landfill leachates, pretreated by
physical and chemical methods and
treated biologically, were separated and
concentrated in semi-batch, steady-state,
and unsteady modes of operation.
Physical/chemical pretreatment with lime
was found necessary to remove
suspended and colloidal matter, heavy
metals, and dispersed oil phases in the
raw leachate; these constituents can
cause membrane fouling and rapid flux
loss.
All physically, chemically, and
biologically treated leachates were
separated to produce clear, turbidity-free
permeates. Eight landfill leachate
experiments were conducted over
extensive periods of time. For example,
high-strength, pretreated leachate EPA
#07 with conductivity of 30,000
micromho/cm, IDS of 27,000 mg/L, and
TOG of 6,700 mg/L was separated and
concentrated in a semi-batch, unsteady
experiment. At room temperature and
moderate feed pressure (approximately
400 psig), inorganic solute rejection
exceeded 95%. During feed
concentration in the retentate (concen-
trate) recycle mode, operation was
limited to feed IDS concentrations of
less than 30,000 mg/L. Flux became
unacceptably low and pressure had to be
increased to overcome the high osmotic
pressure of the feed. In addition,
concentration polarization appeared to
occur at high recoveries accompanied by
high-feed IDS concentrations. When
feed was too concentrated, solutes may
have exceeded solubility limits and
caused additional deposition of mem-
brane surfaces.
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Moderate-strength leachates were
renovated to a greater extent. In a study
with a recovery of 75% at 170 hr of
operation, initial and final rejections for
inorganic species were in excess of 99%.
Initial TOC rejection was low but
increased, with time, to over 70%. This
phenomenon of increasing TOC rejection
is explained by the fact that the more
permeable solutes were purged from the
system early in the process, thus leaving
the feed with organic species that were
rejected continually at higher efficiencies
as time/recovery advanced. No fouling
was observed in any of the moderate-
strength leachate studies.
Biologically-treated landfill leachate
was renovated successfully. TDS and
conductivity rejection were in excess of
98%; maximum TOC rejection was 94%.
Bulk permeate TDS and TOC con-
centrations of 47 and 14 mg/L
respectively, were obtained at recoveries
of over 60%. No fouling was observed in
this study; flux averaged 0.29 m3/m2d.
Lagoon sludge extracts, resembling
industrial landfill leachate, were also
treated with an RO process. In a steady-
state experiment, conductivity and TDS
rejections averaged 97% and 99%,
respectively; TOC rejection was 79%. A
slight increase in rejection and decrease
in flux appeared evident, possibly
because of the formation of a nonfouling
gel layer.
Ultrafiltration
Results of UF experiments indicated
that a high proportion of the organic
matter in leachate samples had a
molecular weight below about 500. This
agrees well with results in the literature
from similar experiments. For raw
leachate and lime-treated leachate,
approximately 80% and 85% of the
organic solutes had a molecular weight
below 500, respectively. These results
suggest that leachate samples contain
primarily synthetic organic compounds
and lesser amounts of biogenic matter,
such as proteins and humic and fulvic
substances. These observations were
expected, since the leachate was
generally of an industrial rather than a
biochemical origin.
Since most organic solutes in leachates
studies do not pass the 500 MW
membrane, the utility of UF for efficient
removal of organic contaminants is
subject to question. At best, UF can be
used as a pretreatment process to
remove high molecular weight
compounds that interfere with other
treatment technologies, i.e., RO.
This UF study confirmed the
pretreatment study results; lime
treatment did not remove a significant
mass of the organic solutes from
industrial landfill leachate samples. The
UF investigation suggested that lime
treatment may remove organic species
with molecular weights greater than
10,000; these represent a relatively small
fraction of the total organic matter
present in solution.
Although membrane UF may not be
effective for removing organic matter of
low molecular weight from leachate, it is
a valuable tool for evaluating the nature
of a leachate sample and the
effectiveness of other pretreatment
processes. UF is not an effective
treatment technique, since it does not
eliminate any of the low molecular weight
organic matter that is destroyed
efficiently by biological renovation.
Conclusions
Several important conclusions can be
drawn based on the study results. These
are summarized in the same order as the
sections of this summary.
Pretreatment
- Treatment of aqueous wastes with
significant concentrations of
dispersed or suspended phases —
high levels of turbidity—by mem-
brane or biological techniques either
was not possible or inefficient without
pretreatment to produce a
homogeneous aqueous phase.
- Lime addition to pH 12, followed by
floe separation and recarbonation to
pH 7 (addition of CO2), was an
effective pretreatment process that
resulted in greater than 98%
reduction in turbidity.
Microbial Treatment
- Aerobic mixed microbial populations
degraded a significant fraction of the
dissolved organic solutes present in
some leachates (80% to 90%), while
being inherently limited in degrading
dissolved organic solutes in other
leachates (< 50%).
- Aerobic mixed microbial populations
may require a readily biodegradable
co-substrate to mineralize
anthropogenic compounds (co-
metabolism) and may exhibit two
distinctive growth regimes.
-Anaerobic mixed microbial
populations degraded a significant
fraction of the dissolved organic
solutes present in some leachc
(60% to 70%).
- Anaerobic mixed microb
populations degraded sevc
chlorinated hydrocarbons presen
aqueous solution from ini
concentrations up to 20 mg/L to I
concentrations below the detec
limit of 20 pg/L. Half-kill doses
toxicity inhibition levels w
determined.
- Methanogens were most likely
group of organisms responsible
degradation of the chlorina
compounds considered.
- Soil-based sequential aerobic/
aerobic microbial degradat
mineralized between 90% and 9
of the dissolved organic solt
present in all leachates test
Carbon dioxide and methane w
principal end products.
- Soil-based anaerobic microbial C
radation reduced TCA
contaminated groundwater from
mg/L to less than 20 pg/L. (
production rates and c
composition indicated tl
methanogenesis was the control
process.
- Three pilot plants were design
constructed, and operated in the f
to demonstrate process feasibility
the following wastes:
(a) An industrial landfill leachate '
treated using a soil-bas
sequential aerobic/anaero
microbial process with sim
pass organic destruct
efficiencies between 90% ,
97% .
(b) In-situ sludge extraction \
coupled with soil-bas
microbial treatment of the
covered extract to demonsti
controlled, rapid removal ;
mineralization of extracta
organic species, with treatrr
efficiencies greater than 95%
(c) TCA in groundwater v
reduced from 5 to 20 mg/L
less than 20 pg/L, utiliz
anaerobic soil-based micro
treatment.
Pilot plants (a) and (b) treated waj
from CERCLA-NPL sites. Pilot studies
and (c) were conducted on site.
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Sorption and Extraction
- Activated carbon adsorption was
inefficient when dispersed oily phases
were present in the aqueous waste.
- Relationships between equilibrium
organic loading and equilibrium
concentrations were dependent on
initial conditions.
- The mass fraction of organic matter
strongly influenced the sorptive
capacity of a soil.
- A landfill leachate solute matrix can
significantly alter aqueous/organic
phase solute partitioning.
Membrane Separations
- RO was effective for removing
inorganic species after biological
treatment.
- UF was an effective tool for
characterizing leachates, but was of
limited value for treatment because a
majority of the solutes present had a
molecular weight less than 500.
-------
Robert C. Ahlert and David S. Kosson are with the Department of Chemical and
Biochemical Engineering, Rutgers University, Piscataway, NJ 08855-0909.
John E. Brugger is the EPA Project Officer (see below).
The complete report, entitled "Treatment of Hazardous Landfill Leachates and
Contaminated Groundwater," (Order No. PB 89-124 6481 AS; Cost: $28.95,
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:
Releases Control Branch
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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