United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-92/035 April 1992
Project Summary
Separation of Hazardous
Organics by Low Pressure
Membranes: Treatment of Soil-
Wash Rinse-Water Leachates
D. Bhattacharyya and A. Kothari
Soil washing is a promising technol-
ogy for treating contaminated soils. In
the present work, low-pressure, thin-
film composite membranes were evalu-
ated to treat the soil-wash leachates so
that the treated water could be recycled
back to the soil washing step. Experi-
ments were done with SARM (Synthetic
Analytical Reference Matrix) soils. Mem-
brane performance was evaluated with
, leachates obtained from different wash
solutions. The effect of fine suspen-
sions in the leachates was also studied.
A solution-diffusion model was modi-
fied to include an adsorption resistance
term in water flux, and this term was
correlated with bulk concentration us-
ing the Freundlich isotherm. This corre-
lation was then used to predict water
flux drop at different bulk concentra-
tions or to predict water flux at different
recoveries. Thin-film composite mem-
branes were found to effectively treat
the leachate from rinse water used to
wash contaminated soil. In addition, feed
preozonation significantly improved
water flux.
This Project Summary was devel-
oped by EPA's Risk Reduction Engi-
neering 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
Soil contamination is one of the major
environmental problems of today. Recently
enacted legislations and the high costs
and high energy requirements associated
with conventional excavation and incinera-
tion, with subsequent disposal in a landfill,
have created a need for innovative, cost-
effective technologies for cleanup. Soil
washing is apromising technology for treat-
ing contaminated sites, and it is one of the
most successful full-scale technologies
developed in Europe for site remediation.
Cost-effective remediation by soil washing
would, however, require simultaneous de-
velopment of effective rinsate treatment
techniques for separating and concentrat-
ing dissolved hazardous pollutants in the
; wash water and recycling back the treated
water for soil washing. These needs were
the motivation for the present work. Previ-
ous research on removal of contaminatants
from leachates by low pressure membranes
and pre-ozonation was also performed.1'2
Membrane processes provide a very
promising treatment technology for this
particular purpose—treating soil-wash
rinse-water leachates. Membrane separa-
tion processes consume less energy than
conventional processes, and membrane
systems are compact and modular. Micro-
filtration, ultrafiltration, reverse osmosis
(RO), and electrodialysis are fully devel-
oped membrane technologies, and
pervaporation is a developing membrane
technology. In recent years, RO has
emerged as a fully developed, mature tech-
nology, and the estimated worldwide sales
of RO membranes in 1988 were $118
million with a projection of $335 million for
1998. Considerable information is now
available for full-scale application of RO
technology in terms of membrane materi-
Printed on Recycled Paper
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als, module design, and cost estimation.
High-pressure RO membranes are used
for sea water desalination (osmotic pres-
sure - 2.34 MPa), and low-pressure RO
membranes are used traditionally for brack-
ish water desalination (osmotic pressure -
0.1 to 0.28 MPa). Low-pressure RO mem-
branes have lower capital and operating
cost, and because of low pressure require-
ments, they can be used in spiral element
design, thus minimizing membrane foul-
ing. For 3,785 L of purified water, the
energy requirements of a high-pressure
RO process are about 3 to 4 times that of a
low-pressure RO process (1.38 to 2.76
MPa), and distillation is about 8 to 18 times
that of a low-pressure RO process. Thin-
film composite membranes provide high
water flux and higher rejection. The os-
motic pressure of most hazardous waste
streams is in the range of that of brackish
water. In view of these attractive proper-
ties, it was decided to use low-pressure,
thin-film composite membranes to treat the
laachates from rinse water used in soil
washing. The ultra-low-pressure RO pro-
cess (or nanofiltration) can be used in
combination with low-pressure RO because
a nanofiltration membrane permeates
monovalent ions but rejects divalent and
multivalent ions, as well as organic com-
pounds having molecular weights greater
than 200.
This work deals with the use of thin-
film, low-pressure composite membranes
for concentrating and separating hazard-
ous pollutants in the soil-wash rinse-water
leachates from SARM soils. Soil washing
experiments were done with different wash
solutions (pure water, nonfonic surfactant
solutions, and EDTA solutions). The sepa-
ration characteristics of the membranes
were evaluated in terms of membrane feed
total organic carbon (TOO), heavy metal
concentration, dissolved solids, suspended
solids, pH, presence of specific compounds
in the feed, feed preozonation, extent of
recovery, and water flux. In addition, the
flux drop results were correlated by using a
solution-diffusion transport model contain-
ing an adsorption term.
Experimental
Figure 1 gives an overview of the differ-
ent experiments and studies done. Most of
the experiments were done with SARM IV.
For soil washing experiments, a 10:1 wash
solution-tosoil ratio was used for all experi-
ments. Mixing time was fixed for 1 hr, and
for most of the experiments, a single rinse
was done. For most of the experiments,
suspended solids from the leachate were
removed by vacuum filtration with the use
of a ,0.22-u.m pore-size filter. Membrane
Washing Solution
Distilled
Water
Wash
Triton
Wash
EDTA
Wash
SARM
Mixer
Soil:Water::1:10
1 hour mixing
Supernatant
Retentate-**-
FT30 Membrane
System
AP= 1.72 MPa
Well-Mixed
Vacuum
Filtration
Suspended
Solids
Filtered Leachate
i
I
Ozonation
Membrane Feed
TOC = 80 to 160 mg/L
Permeate
Analysis
TOC
GC/MS
AA
pH
Conductivity
Dissolved Solids
Suspended Solids
Figure 1. Schematic of the overall experimental plan.
studies were mostly done in a batch sys-
tem at a system pressure of 1.75 MPa.
High mixing conditions were maintained.
The continuous run (in the presence of
suspended solids) was also done at the
same system pressure, and a pump pro-
vided a flow of solution through the con-
tinuous cell. The membrane was cleaned
with a 10% to 30% water-methanol solu-
tion. Feed was preozonated in a 500-mL
stirred reactor with a flow of 0.2 standard
L/min O2 containing 2% ozone.
Filtered leachates, membrane feeds,
retentates, and permeates were analyzed
by TOC analyzer, atomic absorption spec-
trophotometer (AA), and GC/MS. Some
analyses were also done by a U.S. Envi-
ronmental Protection Agency support labo-
ratory.
Results and Discussion
The consistency of distilled water fluxes
and sodium chloride rejections over an
extended operating period (> 200 days)
demonstrated that the FT30* membranes
used were stable. Figure 2 summarizes (1)
the membrane performance with leachates
obtained by washing SARM IV with differ-
ent wash solutions and also (2) the perfor-
mance with ozonated leachates. The
distilled water fluxes for all the experi-
* Mention of trade namesx>r commercial products does
not constitute endorsement or recommendation for
use.
-------
100
% Flux Drop
%TOC
Rejection
% Conductivity
Rejection
% Unaccounted
TOO
Figure 2. Summary of membrane performance with different leachates for SARMIV (A = EDTA wash solution; B = surfactant wash solution; C =
distilled water wash; D = ozonation).
merits were in the range of 9 to 12 X 10-4
cm/s, and the pH of the membrane feeds
were in the .range of 5.8 to 6.8. Membrane
runs recovery ranged between 17% and
80%. For the EDTA wash, 1.01 mol/L EDTA
was used; for surfactant wash, 0.04% Tri-
ton X-100. For the ozonation experiment,
ozonation time was 10 min. Figure 3 com-
pares the typical water flux behavior of
distilled water wash leachate and surfac-
tant wash leachate. There was a 10%
higher flux drop after 17% recovery for
surfactant wash leachate, but as indicated'
in Figure 2, there was a 5% decrease in
amount of organics adsorbed on the mem-
brane surface (% Unaccounted TOG). This
could be because of the surfactant's ability
to form micelles and bind hydrophobic or-
ganics. Figure 2 also shows that TOC
rejections and conductivity rejections were
high, which indicated good membrane per-
formance. Table 1 shows the effect of
EDTA wash on soil teachability of Cu, Ni,
Pb, and Zn and their rejections by the
membrane. EDTA washing 'enhanced
leachability of metals. This could be ex-
plained by the higher stability of metal-
EDTA complexes. For almost all the runs,
the rejections of metals were 92% to 98%.
Figure 4 shows the water flux behavior for
ozonated and nonozonated leachates. For
the ozonated leachates there was only a
5% flux drop; for the nonozonated
leachates, the flux drop was between 20%
and 25%. This suggests that ozonated
products do not interact strongly with the
membrane.
Raising the pH of the leachate precipi-
tated some heavy metals and also re-
moved some TOC with the precipitate.
When the pH of the leachate was lowered
some white cloudiness formed. The pres-
ence of fine suspensions for a low recov-
ery reduced organic adsorption on the
membrane surface. At a high water recov-
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ary (80%), total dissolved solids (primarily
inorganics) contributed significant osmotic
pressure. To predict water flux at different
recoveries, the solution-diffusion transport
model was modified to include an adsorp-
tion resistance term. Figure 5 shows that
experimental and predicted values (at high
water recoveries) agreed well. The ad-
sorption resistance term was correlated
with bulk concentration using the Freundlich
isotherm.
Conclusions
This study has shown that thin-film,
composite membranes can effectively treat
soil-wash rinse-water leachates to produce
permeates for reuse. The permeate can
ba recycled back to the soil washing step.
If the permeate needs to be discharged,
further treatment may be required. The
treatment of the concentrated stream would
be much easier and cost-effective because
of the reduced volume to be treated. The
advantages of this membrane process
are that it is compact and modular and it
has high solute separations at low pres-
sures ( < 2 MPa ), high water flux, low
energy and capital costs, and broad pH
operating range. If EDTA recovery is also
one of the objectives, then a loose RO
membrane like a nanofiltration membrane
may be used to recover EDTA with further
treatment of the permeate. In addition, the
ozonatfon-membrane process would effec-
tively reduce the flux drop and increase
the over-all rejections.
Membrane rejections were found to be
high in terms of selected compounds: pen-
tachtarophenol (> 98%), 4-aminobiphenyl
(> 93%), ethylbenzene (> 97%), xylene (>
81%), 4-chtoroaniline (> 90%), and 2,4-
din'rtrophenol (> 98%). At 80% water re-
covery, there was increased flux drop due
to increased osmotic pressure of total dis-
solved solids and increased adsorption of
sparingly soluble organtcs on the mem-
brane because their solubility limit was
exceeded. Feed preozonation, EDTA wash,
and surfactant wash reduced adsorption of
organfes on the membrane. The modified
solution-diffusion model was in good agree-
ment with the experimental values in pre-
dicting water flux at different recoveries.
The full report was submitted in fulfill-
ment of Cooperative Agreement No.
CR814491 by the University of Kentucky
under the sponsorship of the U.S. Environ-
mental Protection Agency.
14 -I
12-
10-
8 -
6-
4-
2-
System: SARM IVLeachate
A P: 1.75 MPa
pH=5.15to6.0
%r = 17.0% to 17.8%
• Distilled Water
•&400 mg/L Triton X-100
10 20 30 40 50
Time (mm)
60 70 80 90
Figure 3. Permeate flux verses time for leachate after washing SARM IV with distilled water
and surfactant (0.04% Triton X-100).
Table 1. Summary* of Effect of EDTA Washing on the Leachability and Rejection of Certain
Metals
Active
Ingredient
mmoles/L Cu
0 1.58
0.10 20.7
Feed, mg/L
Ni
10.5
14.4
Pb
1.72
8.19
Zn
224
372
%r
17.8
18.7
Rejection, %
Cu
96.2
>99.5
Ni
93.1
>99.3
Pb
96.5
>98.8
Zn
93.3
97.5
' Conditions:
SARM IV:Wash Solution::1:10
AP= 1.75 MPa
Chelant = Versene 100EP (TOC =13.1% with 39% Active Ingredient)
Active Ingredient = Na4EDTA.4H2O
-------
14-
12-.
10-
^
"t 81
I
6-
4-
2-
0-
System: SARM IV Leachate
A.P:1.75MPa
pH=6.5
%r = 21to23%
A no ozonation (TOC=121 mg/L)
• 10min ozonation (TOC=84 mg/L)
•&30 min ozonation (TOC=68 mg/L)
10
20
SO
60
Figure 4.
30 40
Time (mm)
Permeate flux versus time for SARM IVIeachate ozonated for different times.
70
References
1. Bhattacharyya, D., and Williams,
M.E., "Separation of Hazardous Or-
ganics by Low Pressure Reverse
Osmosis Membranes—Phase II, Fi-
nal Report," EPA/600/2-91/045 (Jan.
1992)
2. Bhattacharyya, D., Barranger, T.,
Jevtitch, M., and Greenleaf, S.,
"Separation of Dilute Hazardous Or-
ganics by Low Pressure Composite
Membranes," EPA/600/2-87/053
(1987).
14-
13-
12-
•
11-
10-
9 -
8-
•
7-
*-
5-
4-
3-
2-
1-
0-
i
10
pH=6.3
System:SARM IV Leachate
AP:1.7SMPa
TDS=1420mg/L
* Experimental
- Predicted
20 30 40 50 60
% Recovery
70
80
90 100
Figure 5. Experimental and predicted water flux with percent recovery.
•&U.S. GOVERNMENT PRINTING OFFICE: W92 - 648-080/J0229
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D, Bhattacharyya and A. Kothariare with the University of Kentucky, Lexington,, KY
40506.
Richard Lauch is the EPA Project Officer (see below). '
The complete report, entitled "Separation of Hazardous Organics by Low Pressure
Membranes: Treatment of Soil-Wash Rinse-Water Leachates," (Order No. PB92-
153436/AS; Cost: $26.00, 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
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/SR-92/035
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