United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/023 Jan. 1990
v°/EPA Project Summary
Synthetic Organic Compound
Rejection by Nanofiltration
J. S. Taylor, S. J. Duranceau, L. A. Mulford, D. K. Smith, and W. M. Barrett
A study was conducted to evaluate
the rejection of six synthetic organic
compounds (SOCs) from a potable
water source by a nanoflltration
membrane process. The SOCs were
ethylene dlbromide (EDB), dibromo-
chloropropane (DBCP), chlordane,
heptachlor, methoxychlor, and ala-
chlor. To investigate SOC rejection, a
membrane pilot plant was con-
structed that utilized a single, 4- by
40-inch FllmTec N 70* spiral wound,
thin film composite membrane with a
molecular weight cutoff of 300. The
effects of different operating pres-
sures and membrane feed stream
velocities on membrane rejection of
SOCs are reported. Trihalomethane
formation potential (THMFP), total
organic halide formation potential
(TOXFP) and general water quality in
and out of the membrane are also
reported. Accurate organic and inor-
ganic mass balances were con-
ducted on solutes.
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
The purpose of this cooperative agree-
ment was to determine the capability of a
nanofilter membrane to reject SOCs from
a potable water source.
The scope of work involved selecting a
potable water site, building a membrane
"Mention of trade names on commercial products
does not constitute endorsement or recom-
mendations for use
pilot plant, securing and preparing the
SOC feed, operating the pilot plant,
analyzing the data and reporting. Only
one nanofilter membrane was used for
this project because of economic con-
straints; however, the selected mem-
brane, a FilmTec N 70 nanofilter with
molecular weight cutoff (MWC) of 300,
had been used at four sites on other
projects because the N 70 controlled
permeate THMFP to less than the THM
MCL of 0.10 mg/L and was as productive
as any membrane that successfully con-
trolled THMFP.
Site Selection
The initial site selected for this project
was at Flagler Beach, Florida, so that the
project could be done at the same time
as another project investigating the long-
term cost and performance of membrane
processes to control THMFP at the same
site.The Flagler Beach water treatment
plant had, however, no means to accept-
ably discharge the SOC-contaminated
stream. Because complete containment
of the SOCs was not feasible, the SOC
project site was at the University of
Central Florida (UCF) in Orlando, FL.
After two attempts to use the UCF
irrigation water storage tanks, the pilot
plant was moved to a site adjacent to the
UCF wastewater treatment plant. A 4-
inch-diameter 206 foot-cased deep well
was drilled into the Floridan aquifer—the
same aquifer used by UCF and the
majority of Florida utilities for drinking
water. The SOC-contaminated membrane
streams were discharged to the UCF
wastewater treatment plant.
Pilot Plant Construction
A 14- by 12-foot by 3-inch concrete
pad was poured adjacent to UCF
-------
wastewater treatment plant and the Civil
and Environmental Engineering field
laboratory (CEEFL) building. A 10-foot
cube, steel research building was
assembled on the pad. The research
building had a 110/220 amp power line,
lighting, ventilation fans, a locked fence,
and raw water. A flow diagram of the
membrane pilot plant built for SOC
removal is shown in Figure 1. Well water
was pumped through one of two parallel
1 p prefilters, a totalizer, and back flow
prevention device. Following prefiltration,
H2S04 was added to control CaC03
scaling and the desired SOC was added.
The acid and SOC-containing water then
passed through a high pressure pump
that pushed the water through the
membrane. Chlordane, heptachlor, me-
thoxychlor, DBCP and EDB feed stock
was prepared by first dissolving the SOC
in an organic solvent, acetone or
methanol, and then diluting the SOC
solution in permeate water. Organic
solvents were necessary because the
pure SOCs were insoluble in water.
Alachlor was obtained as a water-soluble,
formulated compound and was directly
dissolved in water for SOC feed stock
preparation.
Operation
The membrane was installed in a
donated custom Mitco* skid, which
consisted of flow and pressure gauges on
feed, permeate, and concentrate lines;
the pressure vessel; and the high
pressure pump with concentrate and
pump recycle lines, all of which were
mounted on a steel frame. Flow and
pressure readings were monitored daily
by gauge readings and direct flow
measurement of the concentrate and
permeate streams. The membrane feed,
permeate, and concentrate stream SOC
concentration was monitored 13 times
during a 31-day period that was divided
into four different recovery periods and
one flushing period. The membrane pilot
plant was operated at approximate
recoveries of 10% (10%R), 30% (30%R),
30% with recycle (30% RR) and 50% with
recycle (50% RR). Samples were taken
after the end of each period of operation
to determine if any adsorbed SOCs could
be flushed from the membrane. 0
solutes in the membrane feed, perm-
and concentrate streams were monito
once during each recovery period. Tr
were THMFP, TOXFP, dissolved org
carbon (DOC), color, total hardness ('
calcium hardness (CaH), alkalinity (i
pH, total dissolved solids (TDS), sod
(Na), sulfates (S04) and iron (Fe).
The feed permeate and concenti
stream flows were typically 4.8, 4.3,
0.5 gpm for 10%R; 3.3, 2.3, and 1.0 £
for 30%R; 3.6, 2.3, and 1.3 gpm"
30%RR; and 2.8, 1.4, and 1.4 gpm
50%RR. The approximate pressure dn
and membrane feed stream velocities
each recovery were 62 psi and 1 f/sec
10%R, 93 psi and 0.6 f/sec for 30°.
107 psi and 1.1 f/sec for 30%RR, i
150 psi and 1.0 f/sec for 50% RR. "
membrane flux ranged from 10 g/sfd
30 g/sfd, increasing with recovery.
water mass transfer coefficient (M"
averaged 0.21 g/sfd-psi (0.021 day
The water production was very const
from the membrane, which operal
5137.7 hr out of a total 5202.5 availa
hr during the SOC project. Only 14.C
Surge
Tank
206'
Well
Stainless
Steel Screen
113 hp
Pump on
Bottom of
Well
Parallel
Filter Tanks
84 Sq. Ft of
Surface Area
Emergency Bypass
Totalizer
—<$—
Manifold
/
Back-Flow
Prevention
Oewce
Sealed
Mixing
Tank
H2SO4
Feed
55 Gallon
Nalgene
Tanks
Permeate
Permeate
Sample Port
A p%rte KSS
t Ce G«**
Concentrate
I Concentrate . * , A
n Flow Concentrate
& Gauge Pressure
Concentrate Gauge
Sample Port
t
N 70 Pressure Vessel
-------
of maintenance were needed for prefilter
replacement and small repairs. The re-
mainng 50.8 hr were spent waiting on
lighting installation which was not attribu-
table to the mechanical operation of the
membrane pilot plant.
Following NaCI injection, the transient
response of the membrane was deter-
mined to be accurately modeled by a first
order system with a time constant of 2
min. Although initial sampling for each
new SOC was done at least 4.0 hr after
operation had begun, 99.9% of any
permeate or concentrate concentration
change would be complete in 13.8 min
following initiation of the change.
The smallest molecular weight (MW)
SOC was EDB (187.9). EDB feed stream
concentration ranged from 260 to 22.4
iig/L during 785.1 hours of operation and
from 88.4 to 22.4 ng/L in the final 443.5
hr, after the operation was stabilized.
Some EDB rejection was observed for
the first four samples collected; however,
the membrane had been permanently
fouled at the initial UCF location and was
replaced after the second sample had
been collected. Only 66% of the EDB
had been accounted for when the fouled
membrane was used. Routine operation
of the membrane pilot plant was not
achieved until after the fourth sample was
collected. Some EDB may have ad-
sorbed onto the fouled membrane during
a period that was not representative of
normal operation. No EDB rejection was
observed for the final seven samples
taken over the last 443.5 hr of EDB
operation. Ninety four % of all the EDB
input to the membrane was recovered in
the concentrate and permeate streams
for the entire EDB operation.
DBCP (MW 236.4) was fed to the
membrane in concentrations varying from
41.5 to 83.5 pg/L over 667.1 hr of
operation. Partial rejection of DBCP by
the membrane varied from 19.6 to 60
ng/L in the permeate stream or 19% to
52%. DBCP permeate concentrations
varied inversely with the water flux and
could be described by a diffusion pro-
cess. The DBCP MTC varied from 2.79 to
7.43 f/day and averaged 4.27 f/day.
The membrane, under all operating
conditions, completely rejected the four
remaining SOCs: chlordane (MW 409.8),
heptachlor (MW 373.3), methoxychlor
(MW 345.7), and alachlor (MW 269.8).
The detection limit for each of these
SOCs was 0.6 iig/L. The absence of any
SOC concentration in the permeate indi-
cates they were sieved from permeate
and were too large to pass through the
yore of the membrane.
The cumulative recovery of SOC in the
membrane output was, in order of their
MW, 94% for EDB (MW 187.9), 96% for
DBCP (MW 236.4), 100% for alachlor
(MW 269.8), 91% for methoxychlor (MW
345.7), 92% for heptachlor (MW 373.3),
and 90% for chlordane (MW 409.8). Only
EDB was found in any flushing samples;
this amounted to less than 0.01% of the
total EDB and was only 0.2 ng/L in the
flushing sample taken 46 hr after EDB
feed was discontinued. No previously fed
SOCs were ever found in any succeeding
SOC analysis. The SOC mass balance
indicated the higher MW SOCs were
adsorbed onto the membrane and did not
release during operation. If adsorption is
a SOC removal mechanism, however,
then SOC breakthrough could occur fol-
lowing longer periods of operation.
The summary of the SOC-rejection
membrane project is shown in Table 1.
The average MTC for 30R and 30RR is
shown because recycling the concentrate
had little effect on the MTCs. The
membrane rejection of TOXFP, THMFP,
and DOC was greater than 90% when
acetone or methanol was not used to
prepare SOC feed stock. Permeate
TOXFP, THMFP, and DOC concentra-
tions averaged 35 ng/L, 6 iig/L, and 0.1
pg/L; this represented 93%, 95%, and
95% rejection, respectively. The recovery
of all DOC in the membrane output was
102%.
As shown in Table 1, the rejection of
the inorganic solutes increased by
species charge and molecular weight.
The rejection of the highest charged and
largest MW species (SO4-2) was 100%.
Rejection of the lowest MW and lowest
charged species (Na*) was 64%, the
least of any inorganic species monitored.
Recovery of inorganic species mass was
102% for all species except Fe and Alk
which were 104% and 98%.
The percent rejection versus MW for
inorganic solutes and organic SOCs is
shown in Figure 2. Membrane rejection of
SOCs is controlled by species MW. All
SOCs with MW greater than 269.8 were
completely rejected. The SOC with MW
187.8 was not rejected, and the SOC with
MW 236.4 was partially rejected. More
highly charged inorganic species with
MWs less than 187.8 (EDB) were re-
jected by the same membrane. The
permeate stream concentration of all
partially rejected species tended to
decrease as water flux increased and to
increase as feed stream concentration
increased, as would be expected in a
diffusion controlled process. Velocity of
the membrane feed streams correspond-
ed to Reynolds numbers of less than 113.
Flow velocity within the membrane varied
from 0.6 to 1.1 f/sec and had no effect on
permeate concentration.
Solute passage through the membrane
involved convection, sieving and diffu-
sion. The mass transport of a small
uncharged SOC that passed completely
through the membrane could be de-
scribed by convection. The mass trans-
port of any partially rejected organic or
inorganic species could be described by
diffusion. The mass transport of SOCs
too large to pass through the membrane
could be described by sieving. The
FilmTec N 70 nanofiltration membrane
had sieving properties of an ultrafilter and
diffusion properties of a reverse osmosis
membrane.
Conclusions
1. The membrane rejected certain
SOCs for a one month period from a
potable water source which indicates
SOC rejection by membranes is a
feasible potable water treatment
process.
2. The rejection of SOCs by the
membrane was dependent on SOC
MW and increased as SOC MW
increased.
3. SOCs with MWs of 269.8 or more
were completely rejected by the
membrane for all operating condi-
tions by sieving.
4. The rejection of DBCP, molecular
weight 236.4, increased as water flux
increased and recovery decreased,
and could be described by diffusion.
5. EDB, the smallest molecular weight
SOC (187.9), was not rejected by
the membrane, which indicated the
mass transport of EDB through the
membrane pores was by convection.
6. The SOC MW determined whether
diffusion could be used to describe
mass transport through the mem-
brane pores.
7. Charged inorganic solutes were
rejected by the membrane at much
lower molecular weights than were
the uncharged SOCs, possibly be-
cause of the electrostatic repulsion
between the ion and membrane.
8. SOC mass balances showed that
SOCs with MWs of more than 345.7
were not completely recovered and
were indicated to have adsorbed
onto the membrane.
9. Solute rejection by the membrane
increased as solute MW or charge
increased.
-------
Table 1. Summary of SOC Membrane Operation
Solvent
Parameter
H#
Species
EDB
DBCP
CWordane
Heptachlor
Methoxychlor
Alachlor
THMFP
TOXFP
DOC
Color
TDS
Alk
TH
CaH
SO4
Fe
Na
Pressure
psi
62
93
107
144
Rejection
%
0
35
100
100
100
100
95
93
95
97
85
78
88
89
700
87
64
Recovery
%
70
30
30 Recycle
50 Recycle
Solute
CP" MTC"
mgIL f/day
— —
0.0372 4.27
< 0.0006
< 0.0006
< 0.0006
< 0.0006 -
0.006
0.035 * -
0.7 0.095
2** -
36 0.363
20 0.647
20 0.239
75 0.226
<7
0.06 0.265
3 7.053
Flux
g/sfd
11
19
22
28
Recovery
%
94
96
90
92
97
700
_
-
702
—
702
98
702
102
102
104
702
* permeate concentration
m mass transfer coefficient
* asCI
* * as cpu
as CaC03
10. Over 90% of the THM and TOX pre-
cursors were rejected by the mem-
brane except when acetone was
used to solublize the hydrophobia
SOCs into feed stock.
11. Water flux was directly proportional
to feed pressure.
12. The membrane system was consist-
ly productive, operating 5138 hr with
only 65 hr of downtime.
13. The transient response of the N 70
membrane was accurately described
by a first order system with a time
constant of 2.0 min.
14. The partial rejection of any solute
could be described by diffusion.
Recommendations
1. The disposal of membrane concen-
trates containing SOCs should be
investigated.
2. Longer operating periods with higher
SOC feed stream concentrations
should be used to determine if sus-
tained rejection of higher MW SOCs
can be attained and to determine if
SOC adsorption is significant for dif-
ferent membrane types and mate-
rials.
3. Membranes differing in surface mate-
rials and pore size should be
investigated for SOC rejection at
higher operating pressures.
4. Rejection of SOCs by membrane
processes should be investigated in
water supplies of varying quality that
are actually and artificially contam-
inated by SOCs so that the effect of
solvent characteristics and SOC com-
petition can be determined.
5. An accurate model for permeate
solute concentration including mem-
brane pore size and distribution,
membrane material, solute and s<
vent mass transfer, recovery, pre
sure, solute size, solute charge ai
temperature should be developed :
that the mechanism of solu
rejection can be explained ar
permeate water quality predicted.
6. An assessment of SOC adsorptk
onto different membrane materia
should be conducted and necessa
SOC adsorption isotherms should t
developed for different membrar
materials in order that a comple
evaluation of SOC membrane adsorj
tion can be made.
7. The effect of turbulence within tr
membrane should be investigated
reduce membrane fouling and permi
ate solute concentration.
8. SOC rejection should be investigate
with a membrane array at recoverie
-------
•*d
I
100
so
60
40
20
Inorganic
Organic (SOC)
100 200 300
Solute Molecular Weight
400
500
Figure 2. Inorganic (A) and organic (*) percent solute rejection versus solute molecular weight
from the SOC investigation using the FilmTec N 70 membrane.
normally experienced by actual mem-
brane plants.
The full report was submitted in partial
fulfillment of Cooperative Agreement
CR813199 by the University of Central
Florida under the partial sponsorship of
the U.S. Environmental Protection
Agency.
-------
J. S. Taylor, S. J. Duranceau, L A. Mufford, D. K. Smith, and W. M. Barrett are with
the University of Central Florida, Orlando, FL 32816.
J. Keith Carswell is the EPA Project Officer (see below).
The complete report, entitled Synthetic Organic Compound Rejection by
Nanofiltration" (Order No. PB 89-194 2451 AS; Cost: $21.95, 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:
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
U.S.OFFICIAL MAIL"
S"9J
Official Business
Penalty for Private Use $300
EPA/600/S2-89/023
i •- i
HluAIc i „»«---
/j.c-i.-jr] -- fl 7 C
'» « , - U O •> \x
0°
*«•«
------- |