United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1-84-018 Jan 1985
SEPA Project Summary
Isolation or Concentration of
Organic Substances from
Water — An Evaluation of
Reverse Osmosis
Concentration
S.C. Lynch, J.K. Smith, L.C. Rando, and W.L. Yauger
This study describes the development
and evaluation of a reverse osmosis
(RO)XDonnan dialysis system for
preparing drinking water concentrates
for biological testing. Commercially
available RO and Donnan membranes
were surveyed for applicability to the
RO concentration method and to
prepare organic concentrates. Two RO
membranes, cellulose acetate
(Osmonics, Inc.)* and FT-30 (Film Tec,
Inc.)*, were selected for laboratory
evaluation, primarily because of their
purported chlorine tolerance. Two
Donnan membranes, Nafion®
(Dupont)* and MA 3475 (IONAC)*,
were chosen for further study based
upon their chemical resistance
characteristics (chlorine, caustic, and
acid tolerance). The FT-30 membrane, a
thin-film composite, demonstrated a
substantially greater rejection
efficiency than the cellulose acetate
membrane. The effect of humic acid, a
natural constituent of potable water
sources, and inorganic salts on the
rejection of model compounds by FT-
30 and cellulose acetate RO
membranes was also evaluated and
found not to be significant under the
test conditions.
As expected from the rejection data,
the recoveries of model solutes were
much better for the FT-30 membrane
system than the cellulose acetate
'Mention of trade names or commercial products
does not constitute endorsement or rec-
ommendation for use
system. Overall the recovery values
(2-74%) were disappointing for the
majority of model compounds in both
RO systems and substantially less than
anticipated based on the rejection data.
This Project Summary was developed
by EPA's Health Effects Research
Laboratory, Research Triangle Park,
NC, 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
In recent years, the trace organic
content of potable water supplies has
been identified as a potential health
hazard Epidemiological studies have
suggested a relationship between the
ingestion of these pollutants in drinking
water and carcinogenic and teratogenic
effects. Although hundreds of organic
compounds have been detected and
quantified in drinking water, the majority
of organic material, i.e., the nonvolatile
fraction, cannot be identified using
currently available technology
Therefore, the direct concentration/isola-
tion of organic contaminants in aqueous
samples for biological testing offers a
practical solution to the determination of
health risks associated with trace organic
contaminants
The Health Effects Research Lab-
oratory - Cincinnati of the U.S. Envi-
ronmental Protection Agency (EPA) has
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funded several independent studies to
determine the effectiveness of different
iso I at i on/con cent rat ion techniques.
Systems or techniques investigated
include reverse osmosis (RO), vacuum
distillation, solid adsorbents, and
supercritical fluid COa extraction. The
necessity of concentrating aqueous
samples prior to biological testing stems
from the trace levels of contaminants and
the lack of sensitivity associated with
existing in vitro and in vivo biological test
systems.
The RO concentration method has
been used previously to prepare
concentrates under several EPA tasks
(EPA Contract Nos. 68-03-2090, 68-
03-2194, 68-03-2367, 68-03-2464, 68-
03-2550, and 68-03-2713) The method
basically involves repetitive batch
concentrations using a RO membrane to
retain organics and reduce the sample
volume (with an accompanying increase
in concentration) by discarding water that
permeates the membrane The Donnan
dialysis process has been used in several
of the concentrations to minimize solids
precipitation resulting from the increase
in inorganic salt concentrations.
Previous studies utilized total organic
carbon (TOC) measurements as a
surrogate to monitor the progress or
efficiency of the concentration Although
TOC is a convenient tool, it is a
nonspecific measurement and provides
little insight about either the rejection or
recovery of specific chemicals. Therefore,
a standard set of model compounds with
differing functionalities, solubilities and
sorption properties were selected to
evaluate this and the other
isolation/concentration techniques
Experimental Procedures
Preparation of Model
Compound Test Solutions
Test solutions of model compounds
used in the membrane screening runs
and in the membrane concentration runs
were prepared by simply diluting the
required volume(s) of stock solution with
organic-free water containing an
inorganic salt matrix. The membrane
concentration runs utilized a "IX" salt
matrix consisting of 70 ppm NaHCOa, 120
ppm CaS04 and 47 ppm CaCI2-2H20. In
the membrane screening runs, a "5X" salt
matrix representing a 5-fold increase in
salt concentration was employed Table 1
lists the final concentration at which each
model solute was tested and the solvent
used in the preparation of individual stock
solutions
Membrane Screening Tests
Four membranes were ultimately
selected for screening tests based on
commercial availability, salt rejection,
stability at pH 5, and the ability to tolerate
a low to moderate free chlorine residual
(<5 ppm) which is commonly
encountered in drinking water. The four
considered to be the most promising were
the cellulose acetate and FT-30 (thin-film
composite) RO membranes, the Nafion®
cation exchange membrane, and the
IONAC MA 3475 anion exchange
membrane. Initial objectives of the
screening tests were:
• To determine specific membrane
rejections with selected model
organic solutes.
• To determine whether levels of
humic acid typical of those
experienced in drinking water
significantly affected the organic
solute rejections
• To determine what trace organic
compounds might leach from the
membranes and to determine what
effect a free chlorine residual might
have on the types of substance(s)
leached from the membranes.
• To determine whether flushing
regimes typical of those used in
previous RO concentrations were
adequate to eliminate contamination
from leachate compounds
• To provide sufficient data to
estimate solute losses to the
membranes and other system
components.
A three-stage screening protocol was
developed to evaluate the selected RO
and Donnan membranes and to address
the stated objectives. The three stages
were flushing, system blank de-
term/nations and membrane solute
screening. Figures 1 and2showthebasic
components of the RO concentration/
Donnan dialysis system used for the
preliminary screening of RO and ion
exchanges membranes
Because all the test runs were
performed using the same basic
membrane screening procedure, data on
the adequacy of the flush procedure were
obtained from each of the runs on
leaching, chlorine exposure, organic
model compound retention and humic
exposure.
One important aspect to be considered
in any system designed to concentrate
organic chemicals from water is the
possible leaching of organic compounds
from components of the system. While
nearly all the elements of the RO system
are fabricated from glass, Teflon, or
Table 1. Model Compounds and the Conditions Used in the Evaluation of the Reverse Osmosis
Concentration System
Concentration (ig/L
Model
Compound
Isophorone
2, 4 -Dichlorophenol
Qumoline
1 -Chlorododecane
Biphenyl
2,4-Dichlorobiphenyl
2,2',5,5'-Tetra-
chlorobiphenyl
2,6-di-tert-butyl-
4-methylphenol
Caffeine
Anthraquinone
S tear ic Acid
bis(2-Ethylhexyl)-
phthalate
Trimesic Acid
Furfural
S-Chlorouracil
Glycine
Glucose
Chloroform
Methylisobutyl
ketone
Humic Acid
Membrane
Screening
Runs
2500
2500
2500
250
2500
250
250
2500
2500
2500
2500
2500
2500
2500
2500
2500
N.T.
2500
2500
2000
Concentration
Membrane
Runs
50
50
50
5
50
5
5
50
50
50
50
50
50
50
50
50
50
50
50
2000
Stock
Solution
Solvent
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
HzO
H20
HZO
Acetone
Acetone
NaOH
Method
of
Detection
GC. GC/MS
GC, GC/MS
GC, GC/MS
GC. GC/MS
GC, GC/MS
GC, GC/MS
GC, GC/MS
GC, GC/MS
GC, GC/MS
GC. GC/MS
GC. GC/MS
GC, GC/MS
HPLC
HPLC
HPLC
Fluorescence
Liquid
Scintillation
GC
GC, GC/MS
HPLC
N. T. = Not Tested
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To Waste r;r^tlnn PumP *»««"">ly
Pump
Donnan
Circulation Loop
Reverse Osmosis
Circulation Loop
Figure 1. Major components of a reverse osmosis (RO) concentration/'Donnan dialysis
organic recovery system.
stainless steel, other components of the
concentration system such as
membranes, adhesives and seals are
made from synthetic organic materials.
Chemical analyses for organic leachables
included examination for low molecular
weight halogenated compounds
(primarily trihalomethanes), semivolatile
priority pollutants by GC/MS (EPA
Method 625), as well as the model
solutes.
It was necessary to evaluate the effect
that low levels of disinfectant would have
on the membranes and other system
components because they are exposed to
residual disinfectant during the
preparation of drinking water
concentrates. The effect of the chlorine
exposure was determined by dosing the
system blank water with sodium
hypochlonte and examining the
recirculated water after 4 hours.
Experiments designed to measure the
ability of the membrane system to
concentrate the model solutes were also
conducted and represented the single
most important aspect of the project. The
two primary objectives of these
experiments were to determine the
membrane's ability to retain the model
compounds (i.e., its solute rejection) and
to determine the extent of losses via
mechanisms such as volatilization,
adsorption, or solubility limitations. Each
of the four membranes (cellulose acetate,
FT-30, Nation®, and MA 3475) were
evaluated in a series of membrane/solute
screening tests. Three samples were
routinely collected during each run. The
recirculating water or feed was sampled
pH monitor/
Controller
NaOH
Concentrate
Bath
HCL
Figure 2. Simplified drawing of a Donnan dialysis test apparatus.
at 5 mm (0.08 hr) and at the end of a 4-hr
period of total recirculation (i.e., where
both the permeate and concentrate are
returned to the process reservoir) to
allow the calculation of solute losses to
the environment and system components
(adsorption, volatilization) A third
sample, taken from the permeate stream,
was collected after 4 hr. By utilizing this
type of sampling program it was possible
to determine solute rejections for each
membrane using Equation 1 and to
estimate system losses by comparing the
initial and final concentrations of solutes
in the recirculating feed solution.
% Rejection = 100
(1 -Cp/Cf)(Eq 1)
where
Cp = permeate cone, of solute
Cf = feed cone, of solute.
Since very little water is transported
across the Donnan (ion exchange)
membranes a permeate sample is not
relevant. Instead, the Donnan
membranes were dialyzed against a salt,
acid, or base solution, and this "strip" or
"pump" solution was sampled at the
same time (4 hr) as the last sample from
the process reservoir. This allowed an
estimation of the amount of solute lost to
the chemical pump solution.
Because humic acid comprises a major
portion of the dissolved organic material
in drinking water, its effect on the
membrane systems and model solute
rejection was surveyed. The
concentration of humic acid varies from
source to source but it is not uncommon
to find 1 -5 mg/L of humic material
present in surface sources. A
concentration of 2 mg/L was selected for
this study
Membrane Concentration Tests
The primary objective of the membrane
concentration tests was to evaluate the
efficiency of the RO/Donnan dialysis
concentration system for concentrating
trace levels of model solutes (1 -50 ppb) in
500L of water.
Figure 3 illustrates the major process-
ing steps in the concentration of 500
liters of organically spiked water. The
concentration was designed to reduce
500 liters to 10 liters and incorporates
two major types of membrane processes,
RO concentration and Donnan dialysis
First, an RO system was used to reduce
(and concentrate) three 167-liter batches
to 13.5 liters each. RO concentration was
temporarily interrupted at 12.6X volume-
tric concentration as this level of concen-
tration was found to approach the in-
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organic solubility threshold. At this time,
the second membrane process, Donnan
softening, was used to reduce the con-
centration of calcium ions and thereby
avoid any inorganic salt preparation
Following the 4-hr Donnan softening
treatment, the RO concentration was
resumed until a 50-fold concentrate was
obtained. A slight volumetric decrease
(with an accompanying increase in
concentration factor) was experienced
during Donnan softening due to osmotic
pumping of water from the concentrate
into the salt "pump" solution.
In Figure 3, the asterisks indicate the
samples that were collected at various
points during the concentration run to
monitor its progress. Three streams were
sampled during each concentration run:
the concentrate (also termed "feed" and
designated F); the RO permeate, designated
P; and the salt pump solution, designated
S.
Results and Discussion
Leaching Studies
Leaching of organic compounds from
the membranes and system components
was studied in two series of tests. In the
first series, the samples were only
examined for model solutes. The existence
of model solutes in the system blanks was
sporadic and at trace levels and probably
represents slow, reversible adsorption
and desorption of spike organic solutes
from earlier exposures to the membrane.
Potential leaching of organic compounds
from the membrane systems was examined
in more detail in the second level of tests
where gas chromatography (GC)/mass
spectrometry (MS) was used in addition
to the routine GC/flame lonization
detector, GC/electron capture detector,
and high performance liquid chromatog-
raphy methodologies In this series of
tests, the effect of chlorine exposure on
the types of leachable organics recovered
in the blanks was also examined. Low
levels of a limited number of solutes
occurred sporadically for all the membrane
types (in the absence of chlorine) with no
strong trends or consistency of results
evident In tests with chlorine present,
the analysis for model solutes did not
reveal any significant variations from the
prior tests, but a greater number and
variety of compounds were detected by
GC/MS. While tentative identifications
could be made only for some of the
compounds, it was important to note that
none of them were obvious chlormation
by-products. Several of the compounds
detected in the FT-30 membrane blank
before and after chlorine exposure were
nitrogen-containing compounds which
may have originated from the barrier
coating of the thin-film composite, FT-30
membrane.
Membrane Screening and
Concentration Studies
Membrane rejection values from both
the screening and concentration runs are
presented in the full report for the
cellulose acetate and FT-30 RO membranes.
Rejection values indicating the effect of
humic acid are also provided.
Several items that require further
explanation are the negative rejection
values and rejections listed as indetermi-
nate values. Negative values result
whenever the organic solute concentration
is higher in the permeate stream than in
the corresponding feed solution. Rejections
listed as indeterminate values resulted
whenever the sample concentrations
were below the analytical detection
limits.
500 Liters
Samples
FCP = 1
cf = s.'
PCF = 8
While membrane rejection may be the
most important single factor in any RO
concentration system, the success or
efficiency is nonetheless measured by
the overall recovery of as many different
types of compounds as possible. Tables in
the full report list the percent mass
recoveries for the three concentration
runs where:
Percent recovery = 100{Cf'VfF/C,FVf)(Eq. 2)
and Cf, Cfp represents the initial and final
concentration of the solute in
the feed, respectively.
vr, VfF represents the initial and final
volume of the feed, respec-
tively.
Upon inspection, the recovery values for
many of the solutes are extremely low,
especially for the cellulose acetate
membrane. Under the experimental
conditions, losses due to adsorption were
considerable
Donnan Membrane
(Softening)
R.O. Permeate
to Waste
Fee - 12 7 ;S
Fcf , 40 • I Jl ^ Ft. 0. Permeate
Per = 40 L to Waste
FCF = so
Figure 3. General experimental design and sampling regime for the reverse osmosil
concentration runs.
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Two major comparisons can be made
from the recovery data listed in the full
report. First, a comparison of the recoveries
of the cellulose acetate membrane (Run
618-41) and the FT-30 membrane (Run
618-51) indicated that in practically all
cases, organic solute recovery by the FT-
30 membrane equaled or more often far
exceeded the recovery demonstrated by
the cellulose acetate membrane. This
was not unexpected since membrane
rejections determined for the two mem-
branes in the screening tests and the
concentration runs reflected this same
trend.
The second comparison was between
the FT-30 tests with (618-57) and without
(618-51) humic acid in the water matrix
There are 12 pairs of data that can be
compared directly For comparison, three
categories were defined 1) higher
recovery with humic acid present, 2)
lower recovery with humic acid present,
and 3) nodifference. Itwasstipulatedthat
the differences were to exceed 10
percent to qualify as significant
The results of this comparison showed
that higher recovery was exhibited for
two compounds, 1-chlorododecane and
2,2',5,5'-tetrachlorobiphenyl, with humic
acid present; and that lower recovery was
exhibited for two compounds, 5-chloroura-
cil and methylisobutyl ketone, in the
presence of humic acid. Eight compounds
showed no change when humic acid was
present in the test matrix.
Adsorption Studies
The mechanism implicated in the
disappearance of most of the solute
material was adsorption, even though
limited solubility, biodegradation, and
chemical decomposition of some solutes
may be complicating factors. Estimates of
solute losses due to adsorption on the
system components were provided by
examination of the extent of model solute
loss during the 4 hr of total solution
recirculation.
Adsorption losses of greater than 70
percent were observed for biphenyl; 2,6-
di-tert-butyl-4-methylphenol; anthraqui-
none, stearic acid and bis(2-ethylhexyl)
phthalate in the presence of humic acid. In
addition to determining the actual
adsorption losses, it was possible to make
comparisons between: 1) the two RO
systems, 2) the RO systems and the
Nafion® membrane system, and 3) solute
solutions with and without humic acid
present. The data indicated no significant
differences in solute losses between RO
membranes; however, the Nafion®
system exhibited significantly less adsorp-
tion than either RO system. Comparisons
of the effect of humic acid in the water
matrix on solute losses to adsorption in
the three membrane systems revealed
appreciable changes in only four instances
for the 12 solutes for which data were
available Because of the magnitude of
scatter and the fact that none of the
changes were greater than 50 percent,
these changes may not be significant
Recommendations
• The FT-30 membrane should be
used in future concentration studies
because of better solute rejection,
recovery, and chemical resistance as
compared to the cellulose acetate mem-
brane.
• Steps should be taken to satisfy
adsorptive demands during sample
collections using the reverse osmosis
concentration method. Preconditioning
of this nature could involve exposing the
membranes and other system components
to water (both at ambient and concentrated
levels) being sampled. This type treatment
should help maximize recovery of organics
in any stream where significant adsorption
may occur
• The apparent losses to adsorption
should be investigated in further detail
under conditions more favorable to
analytical chemistry. By removing some
of the major analytical complications (i e.,
mixed salts, acetone, and humic acid) and
spiking at higher solute levels, better
accuracy will be provided Extended test
periods and expanded sampling schedules
should be instituted to better determine
the attainment of steady-state conditions
and characterize the solute sorption
phenomena. It is expected that more
benefit will be gained from these modifica-
tions than will be lost in deviating from
"real world" modeling Answers to these
questions should be sought.
1. Is the adsorption phenomenon
associated with the membrane or
other system components?
2. Is the phenomenon reversible?
3. Can the "demand" for solute be
satisfied?
4. Is the adsorption a function of the
solute concentration?
• The search should continue for a
better anion exchange membrane. This
membrane is needed whenever concentra-
tion procedures require the concurrent
removal of inorganic burden. Research is
being conducted to develop improved
membranes with polyolefin backbone
structures in the laboratories of several
major membrane manufacturers. These
membranes should possess better chemi-
cal resistance than the styrene/divinylben-
zene based membranes currently in
production. The apparent chlorine sensi-
tivity of the MA 3475 membrane indicates
manufactures' claims may be adequate
for electrodialysis applications, but are
less than optimum for organic sampling.
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S. C. Lynch, J. K. Smith, L C. Ftando, and W. L Yauger are with Gulf South
Research Institute, New Orleans, LA 70126.
H. P.,ftinghand is the EPA Project Officer (see below).
The complete report, entitled "Isolation or Concentration of Organic Substances
from Water—An Evaluation of Reverse Osmosis Concentration," (Order No. PB
85-124 147; Cost: $19.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
--USGPO: 1985 — 559-111/10781
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No G-35
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Penalty for Private Use S300
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