United States
Environmental Protection
Agency
Risk Reduction
EngineeringLaboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/022 Jan. 1990
4>EPA Project Summary
Cost and Performance of
Membranes for Organic
Control in Small Systems:
Flagler Beach and Punta Gorda,
Florida
J. S. Taylor, L. A. Mulford, W. M. Barrett, S. J. Duranceau, and D. K. Smith
A membrane pilot study was
conducted to determine if membrane
processes could remove trihalo-
methane (THM) precursors from
highly organic surface and ground-
waters and consistently maintain
water production for 1 yr at each
location. The scope of this 33-month
project involved: site selection, mem-
brane selection, 1 yr of membrane
pilot plant operation at each site, and
a cost comparison of the membrane
process and the conventional water
treatment process at each site.
The highly organic Florida waters,
a groundwater and a surface water,
were selected. Several membranes
were tested for pilot use by short-
term testing at each site. Although
four membranes controlled THMs to
less than the THM Maximum
Contaminant Level (MCL), the
FilmTec N 70* nanofilter was selected
at each site for long-term use
because of both productivity and
THM control. A three-stage
membrane pilot plant operated at
each site controlled THM formation
potential (THMFP) to less than 0.10
mg/L. Organic and inorganic water
quality, water production, and cost of
treatment were reported for
membrane utilization at both sites.
•Mention of trade names or commercial
products does not constitute endorsement
or recommendation for use.
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
The purpose of this project was to
determine if a membrane process could
maintain consistent water production
while keeping permeate THMFP below
the 0.10 mg/L THM MCL. The scope of
the project was to select both a
groundwater and surface water site that
had a highly organic raw water, select a
membrane for extended operation on
based on THM control and water
production, operate a membrane pilot
plant for 1 yr at each site, monitor
THMFP as well as other water quality
parameters and water production, and
compare the cost of membrane and
conventional processes at each site.
The groundwater site selected for 1 yr
of pilot plant operation was Flagler
Beach. The 0.4 mgd Flagler Beach water
treatment plant (FBWTP), which utilizes
conventional lime softening, is located on
the east coast of Florida near Daytona
Beach and serves a population of 3,000.
The THM concentration in the Flagler
Beach distribution system averages more
than 300 jig/L. Punta Gorda, located on
the west coast of Florida about 80 miles
-------
south of Tampa, was selected for the
surface water site and used Shell Creek
as a raw water source. At the start of the
1 yr of pilot plant operation at this site,
the Punta Gorda water treatment plant
(PGWTP) used an alum-coagulation
process that was being operated in a fill-
and-draw mode. While the pilot plant was
in operation, a new PGWTP, using a
continuous alum-coagulation process,
was placed in operation. At the PGWTP,
the average daily flow was 2.7 mgd for a
service population of about 17,000. At
present, the PGWTP uses chloramines
for disinfection, and THMs in the
distribution system average 80 jig/L.
Before the switch from a free chlorine
residual to chloramines, distribution
system THMs exceeded 300 ng/L.
Membrane Selection
Eight spiral-wound, thin-film composite
membranes were tested at Flagler Beach
for THM precursors and permeate
productivity. Single 4-in. diameter by 40-
in. length membranes were installed in a
small-scale test unit and tested at feed
pressures of 105 to 140 psi at a recovery
of 75%. Four of the membranes
produced a permeate with a THMFP of
less than the 0.10 mg/L THM MCL. Of
these four, the FilmTec N 70 membrane
was selected for the 1 yr pilot plant
operation because its solvent (water)
mass transfer coefficient (MTC) of 0.0137
day1 was the highest of all membranes
tested at this site. Membrane testing at
Flagler Beach showed that a membrane
molecular weight cutoff (MWC) of 500 or
less was needed to remove sufficient
THM precursors for the permeate
THMFP to be less than the 0.10 mg/L
THM MCL. Similarly, an MWC of 300 or
less was needed to reduce permeate
total hardness to 150 mg/L as CaC03.
Ten spiral-wound, thin-film composite
membranes were tested at Punta Gorda
for removal of THM precursors and
permeate productivity. With the use of
the small-scale test unit, the single
membranes were tested under similar
operating conditions using both raw and
alum-coagulated feed waters. Four of the
membranes were able to reduce the
THMFP of the feed waters to less than
the 0.10 mg/L THM MCL. Of these four
membranes, the FilmTec N 70 had the
highest solvent MTC (0.0106 day1 with a
raw-water feed, 0.0048 day1 with an
alum-coagulated feed) at this location and
was again selected for the 1 yr pilot plant
trial. Permeate solute concentrations
were lower for all membranes when the
feed had been alum coagulated first;
however, all membranes whose permeate
THMFP could meet the THM MCL using
alum-coagulated feed, could also meet
the THM MCL using raw-water feed.
Since the FilmTec N 70 membrane
showed greater permeate productivity
(higher solvent MTC) on raw-water feed
than on alum-coagulated feed, a raw-
water feed was chosen to begin the
Punta Gorda pilot plant operation. All
membranes with an MWC of 500 or less
were able to produce a permeate THMFP
that could meet the THM MCL at the
Punta Gorda site.
Pretreatment
The silt density index (SDI) was used
to determine pretreatment requirements
to prevent membrane fouling at Flagler
Beach. The average of three SDI tests
conducted on the Flagler Beach raw
water was 2.2, which is less than the 3.0
maximum recommended for membrane
plant feed waters. The solubility
calculations made to define scaling
problems indicated that calcium
carbonate was the salt limiting recovery.
Based on the manufacturer's recom-
mendations, an initial dose of 6 mg/L of
Pfizer FloCon 100 antiscalent was used.
A flow diagram of the membrane pilot
plant is shown in Figure 1.
The mini-plugging factor index (MPFI)
and the SDI were used at Punta Gorda to
determine pretreatment requirements.
Several different pretreatment schemes
were investigated, including:
-untreated raw water (R)
-raw water plus sand filtration (RSF)
-alum coagulated and settled water
(ACS)
-alum coagulated and settled water
plus sand filtration (ACSSF)
The lowest acceptable MPFI and SDI test
values for membrane processes were for
the RSF pretreatment option, which was
selected for use at pilot plant start-up.
Limiting salt calculations indicated that
calcium carbonate also controlled
recovery at Punta Gorda. A 5-mg/L dose
of FloCon 100 was initially selected to
control scaling.
Operation at Flagler Beach
The FBWTP personnel who operated
the pilot plant at Flagler Beach kept daily
records of pressure and flow. Pilot plant
repairs, makeup of feed chemicals, and
bi-weekly collection of samples were the
responsibility of personnel from the
University of Central Florida. The pilot
plant only operated when the FBWTP
operated, generally about 16 hr per day.
From November 1986 to November 1
the pilot plant operated for 5,098 hr,
64 needed for maintenance. Additi
operating time was lost because of re
delays.
Water production for the year of
plant operation at Flagler Bead
summarized in Table 1. The average 1
pressure was 141 psi, and the avei
recovery was 79%. The average w
flux from stage 1 (S1), stage 2 (S2),
stage 3 (S3) was 12.5, 15.3, and
g/sfd, respectively. Overall system
averaged 12.8 g/sfd. As shown in Fie
2(a), system flux was very consis
during the year of operation.
Average values of the concentrati
of selected water quality parameters
the raw water, the FBWTP finished we
and the membrane pilot plant perme
are listed in Table 2. The perme
THMFP averaged 20 ng/L and v
consistently low throughout the year
shown in Figure 2(b). Stage perme
concentrations were typically in the or
S2 < S1 < S3, which was the inverse
the stage order water flux (S3 < S1
S2) as one would expect in a diffusi
controlled process.
The membranes were cleaned tw
during the year at Flagler Beach. The f
cleaning at 280 hours was necess,
because iron fouled the FloCon 1
antiscalent and the antiscalent lost
ability to prevent calcium carbon;
scaling. The membranes were clean
with sulfuric acid, and a sulfuric acid fe
was substituted for the FloCon 100
prevent scaling. The membranes th
operated until 3,891 hr when the seco
cleaning was done to remove visit
biological growths in the pressure vesse
and transmission lines; it was not do
because of any change in water quality
production. If sulfuric acid had been us
initially for the antiscalent feed, there
no evidence that a cleaning to maint.
water quality or production would ha
been necessary during the year
operation.
Operation at Punta Gorda
The membrane pilot plant operated
total of 6,676 hr from November 1987
November 1988 at Punta Gorda. Pit
plant maintenance required 198 hr
downtime, and additional time was lo
with PGWTP shutdowns and repa
delays. The pilot plant was operated t
PGWTP personnel, with maintenance ar
other duties shared between PGWTP ar
University personnel.
Pilot plant operation was much
difficult at the surface water site. Th
-------
Supply
Pump
uptionai
Holding
lank
C
)
Optional
Sand Fitten
Alum
or
Raw Water
Feed Line
Concentrate
Line
Sample Point n Valve
High
Pressure
Pump
Permeate
Discharge
Pump
Figure 1. Flow diagram For the F/lmTec N 70 Membrane System.
pretreatment indices (SDI and MPFI) did
not accurately predict the extent of
membrane fouling that occurred. The
membranes were cleaned on 20
occasions because of low flux caused by
organic fouling. Several pretreatment
changes were made during the year in an
attempt to maintain the average system
flux above 10 g/sfd. The most significant
of these changes were: (1) the addition of
a second sand pre-filter, (2) a change
from an antiscalent feed to a dispersant/
antiscalent feed, (3) use of alum-
coagulated and settled water from the
PGWTP for the membrane feed, and (4)
use of a sulfuric acid feed to dissolve any
aluminum hydroxide colloids remaining in
the alum-coagulated water after settling.
The most successful pretreatment
configuration was found to be the use of
alum-coagulated and settled water from
the PGWTP, following by two sand
prefilters in series with sulfuric acid
addition and 5-u final filtration. The
average flux and average rate of flux loss
for this pretreatment configuration was 8
g/sfd and 0 05 g/sfd2, respectively. Under
these operation conditions, membrane
cleaning was required about every 16
days to avoid a production loss of greater
than 10%. Product recovery was also
varied from 80% down to 40% in an
attempt to maintain a higher velocity
across the membrane surface to scour
out foulants. Operation at 40% recovery
produced the lowest average flux (7.1
g/sfd), but also least rate of flux loss.
Water production for the year of pilot
plant operation at Punta Gorda is also
summarized in Table 1. As shown in
Figure 2(c), system flux at Punta Gorda
varied greatly because of numerous
membrane cleanings and changes in the
pretreatment configuration in an attempt
to stabilize water production.
Average values of the concentrations
of selected water quality parameters for
the raw water, the PGWTP finished water,
Table 1
Average Water Flux, MTC and Pressure Drop by Stage for Flagler Beach and Punta Gorda FilmTec N 70
Membrane Plants.
Flagler Beach
Location
Stage 1
Stage 2
Stage 3
System
Flux
glsfd
125
15.3
11 1
128
MTC"
1/day
0.015
0.009
0.008
0.005
Recovery
%
38
38
43
79
Pressure Drop
psi
57
101
100
141
"Mass Transfer Coefficient
Punta Gorda
Flux
glsfd
8.0
8.0
9.0
8.2
MTC"
1/day
0.003
0.003
0.040
0.003
Recovery
%
22
17
22
56
Pressure Drop
psi
134
132
119
152
-------
Table 2. Average Values for Raw, Finished Plant and Membrane Water Quality at Flagler
Beach and Punta Gorda FilmTec N 70 Membrane Pilot Plant Operations.
Flagler Beach
Parameter
THMFP (itg/L)
TOXFP (ng/L)
Color (cpu)
DOC (mg/L)
TDS (mg/L)
A/a (mg/L)
TH (mgIL CaCOs)
CaH (mg/L CaCOy)
Cl (mg/L)
Alk (mg/L CaCOJ
PH
Raw
367
1186
30
8.9
625
49
352
327
122
338
7.9
Finished
350
1105
5
7.6
530
49
111
91
122
98
8.3
Membrane
20
33
29
6.8
105
22
35
31
102
35
5.5"
Raw
880
2737
46
20.6
411
44
227
165
85
121
7.4
Punta Gorda
Finished
3821/80"
1414
3
6.4
473
57
222
161
105
116
8.1
Membrane
37
53
3
0.6
99
51
31
24
35
20
3.8"
t THMs formed with free chlorine present over 96 hours
" THMs formed in distribution system with chloramme disinfectant
" Prior to stabilization
and the membrane pilot plant permeate
are listed in Table 2. The feed and
permeate THMFP concentrations are
shown in Figure 2(d) for the year of
operation at Punta Gorda. The permeate
THMFP exceeded the THM MCL on only
one occasion when the new PGWTP was
put on-line. The permeate THMFP
averaged 37 ug/L, which was less than
the average THM concentration of 80
vig/L in the Punta Gorda distribution
system.
An upward shift occurred in the
concentrations of all organic and
inorganic permeate parameters when the
pretreatment was changed to alum-
coagulated and settled feed water
Although alum coagulation removed
many foulants that impeded water flux,
the presence of these foulants may have
resulted in the formation of a tighter
secondary layer on the membrane
surface that would have increased solute
rejection and decreased concentrations in
the permeate.
The order of stage flux before and
after the change to alum-coagulated and
settled-feed water was S1 > S2 > S3
and S3 > S1 = S2, respectively. The
stage order for permeate concentration
before and after the change to alum-
coagulated and settled-feed water was
typically S3 > S2 > S1 and 81 > 82 >
S3, respectively. The stage pressure
drops after the pretreatment change
indicated that less fouling material was
reaching S3, therefore S3 productivity
was increased and S3 permeate
concentrations were decreased. As at
Flagler Beach, the stage and system
solute concentrations were indicative of a
diffusion-controlled process.
Cost
With the use of information obtained
from the pilot plant operation, the
estimated capital and O&M costs for
installing a membrane water treatment
plant of equivalent capacity (0.7 mgd) to
the existing lime softening plant at Flagler
Beach are shown in Table 3. A
membrane plant (including concentrate
disposal) installed at the Flagler Beach
groundwater site would cost less to
operate but would require more to build
because the existing 0.70 MGD lime
softening plant is debt free. Installation of
a membrane plant (including concentrate
disposal) at Flagler Beach with a 2.7
MGD capacity to meet the future demand
for 20 years would essentially cost the
same to build and operate as an
equivalent capacity lime softening plant.
The membrane plants would produce
better water quality than the lime
softening plants.
Similar cost information for the surface
water site at Punta Gorda is given (Table
3). Here, the use of a membrane process
essentially requires the construction of a
complete alum coagulation, sedimenta-
tion, and filtration plant to be used as
pretreatment in front of the membranes.
Thus, the costs for the membrane
operation are considerably higher.
Operating a membrane plant on the
highly organic surface waters found in
Florida would require lower design flux
and recovery, more frequent membrane
cleanings, and very extensive pre-
treatment than would a plant at
groundwater site. The cost of membre
treatment for this type of surface wa
may be unreasonable unless futi
regulations for THMs and disinfecti
byproducts force further consideration.
Summary
A membrane plant, operati
noncontinuously for a year on a grour
water source at Flagler Beach, Floric
produced a permeate of high chemk
quality while maintaining consiste
production. The permeate THMFP w
always less than the current THM MCL
0.10 mg/L. On a unit cost basis, the cc
of constructing and operating equivale
capacity lime softening and membrai
plants would be nearly equal, and tt
membrane plant would produce superi
quality drinking water.
At the Punta Gorda, Florida, surfa<
water source site, the membrane pil
plant could not maintain consiste
production because of severe organ
fouling problems. The permeate THMF
concentration consistently averaged lei
than the current THM MCL, however, ar
was also less than the distribution systei
THMs produced by the existing alui
coagulation plant using chloraminatioi
Additional pretreatment involving alui
coagulation, pH control, and san
filtration was needed to improve produt
tion and lessen the rate of flux los
between membrane cleanings. The Punl
Gorda data indicate that a membran
process designed for a highly organi
surface water source must be based onf
lower design flux and recovery, mor
-------
I
3
1
I
1
I
0.
I
600
500
400
300
200
100
15
12
9
6
3
1500
1200
900
600
300
Operating
Year
Complete
Operating
Year
Complete
Permeate THMFP
Flux
Operating
Year
Complete
Punta Gorda
Feed THMFP
Punta Gorda
Operating
Year
Complete
Permeate THMFP
(A)
(B)
(C)
(D)
1000 2000 3000 4000
Hours of Operation
5000
6000
7000
Figure 2. Water flux and permeate THMFP for the FilmTec N 70 Membrane System at Flagler Beach and Punta Gorda, Florida.
frequent membrane cleanings, and exten-
sive pretreatment. Although constructing
and operating a membrane plant at Punta
Gorda was shown to be more than twice
as costly as the existing alum coagulation
process, the plant would produce a better
quality drinking water.
The full report was submitted in ful-
fillment of CR 813199 by the University
of Central Florida under the sponsorship
of the U.S. Environmental Protection
Agency.
Table 3. Capital and Operation and Maintenance (O&M) Costs for the Present (1988) and Future (2008) Flagler Beach and Punta
Gorda Water Treatment Plants and Equivalent Capacity Membrane Plants.
Present
Location Capacity
Flagler Beach
Punta Gorda
MGD
0.7
8.0
Conventional
O&M
$11000
gal
1.21
0.99
Capital
$
0
3,500,000
Membrane
O&M
$11000
gal
1 09
1.86
Capital
$
1,437,000
12,966,000
Future
Capacity
MGD
2.7
8.0
Conventional
O&M
$11000
gal
0.69
0.99
Capital
$
3,951 ,000
6,971.000
Membrane
O&M
$11000
gal
0.72
1.86
Capital
$
3,840,750
16,338,500
-------
J. S. Taylor, L A. Mulford, W. M. Barrett, S. J. Duranceau, and D. K. Smith are
with the University of Central Florida, Orlando, FL 32816.
J. Keith Carswell is the EPA Project Officer (see below).
The complete report, entitled "Cost and Performance of Membranes for Organic
Control in Small Systems: Flagler Beach and Punta Gorda, Florida,"
(Order No. PB 89-190 367/AS; Cost: $28.95, 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:
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
US.OFFiCiALMAiL
,,•:,; 4' M i W/ATI-
Official Business
Penalty for Private Use $300
EPA/600/S2-89/022
-SI'/ATI- _ r -.
,'ji£S3CC| II ^ *1 -
/» » j -• U «J »* -
V , /- a METER
v C.' \^s :;jro4'i41
00005833 S GE»C,
------- |