Novel Low Fouling Nanofiltration Membranes
Craig Bartels, PhD, Hydranautics, Oceanside, CA Warren Casey, PE, Hydranautics, Houston, TX
Abstract Nanofiltration (NF) has become a standard process to treat mildly brackish water sources that are high in hardness, iron or organic material which forms disinfection by-products. The goal of the membrane in these processes is to selectively remove certain ions, while passing others. Designing these membranes has become more complex in recent years as regulations on the finished water have become tighter, and there is pressure to reduce operating costs. Example of such applications are the 10.5 million gallon per day (mgd) Deerfield Beach and the 40 mgd Boca Raton projects in Florida. The permeate from each of these new plants is blended with existing lime softener effluent. To meet the desired hardness of the blended water, the nanofiltration permeate hardness had to fall within a limited range, 25-80 (Deerfield) or 50-80 (Boca Raton) ppm as CaCO3. In each project the nanofiltration membrane must also reduce trihalomethane formation potential (THMFP) below 40 ppb and meet a maximum pressure requirement (90 psi for Deerfield and 80 psi for Boca Raton). In the case of Deerfield, however, there was a requirement to have high iron rejection as well. As a result, a slightly higher rejection NF membrane was required for Deerfield to achieve the iron reduction targets, while a slightly looser NF membrane was required to achieve the hardness passage requirements of the Boca Raton project. Hydranautics has developed a unique NF membrane which is made by a process that allows the rejection to be tuned to a level that can meet the specific rejection required for these new projects. For the Deerfield project the membrane was made with an average calcium chloride rejection of 86%, while for the Boca Raton project the membrane was made with 80% rejection. As expected, the permeability of the NF membrane for Deerfield is lower, 7500 gallons per day (gpd) compared to the 7800 gpd element for Boca Raton. Information will be reported on the characteristics of these unique membranes, and how they are designed for these unique applications. In addition to meeting the water quality and initial pressure requirements, these applications also have very high levels of TOC in the water, up to 20 mg/l. The high fouling potential of this water also makes it difficult for the NF membrane to maintain stable performance over the life of the membrane. The unique low fouling feature of the ESNA1-LF nanofiltration membrane makes it ideally suited for difficult organic-laden feedwaters. The ESNA1-LF membrane has operated at the Deerfield plant since 2003 and has produced product water of 0.13 ppm iron, hardness of 27.3 ppm as CaCO3, THMFP of 27 ppb, and stable operating pressure. The membranes have not required chemical cleaning during this period. The ESNA1-LF2 membrane at Boca Raton plant has been operating since November 2004. The permeate from the NF membranes has an average hardness of 75 ppm as CaCO3 and THMFP of 16 ppb. Meeting these strict water quality requirements has proven that these new low fouling membranes can be tailored, even for very large-scale plants.
Novel Low Fouling Nanofiltration Membranes
NAMS ’06 Chicago, Ill
Craig R. Bartels, PhDWarren Casey
HydranauticsOceanside, CA
2
Commercial Use of Nanofiltration
37 mgd Mery sur Oise NF Plant (Desal 192 (2006) 303–314)
Pesticide RemovalPartial Ca Removal
9 mgd Boynton Beach NF Plant (AMTA 2005)
Partial Ca Removal 7 mgd Irvine Ranch Deep Aquafer
Organic RemovalTDS Passage
7 mgd Irvine Ranch Deep Aquafer7 mgd Irvine Ranch Deep Aquafer
Organic RemovalTDS Passage
3
New Nanofiltration Application Trends
• Larger Plant Sizes: 10 – 40 mgd• Specific Permeate Hardness Target• High Organic Levels = High Fouling
Potential • Disinfection By-Products Limits• Low Pressure Operation• Timing of Execution
4
New Low Fouling NF Membranes with Variable Hardness Rejection
Controlled hardness removal - eliminating the need for hybrid membrane designs (LF, LF2, LF3 versions)
Greatly reduces fouling potential caused from natural organic matter
Lowest cost per gallon produced – feed pressures of less than 100 psi saves energy cost
Significantly reduces operating costs by lowering power consumption, while providing a non-aggressive low TDS permeate water
5
Membrane Surface PropertiesSmooth Topography
• Surface roughness has been decreased to minimize sites for debris trapping
ESPA3 Surface
ESNA1-LF Surface
6
Membrane Surface Properties:Reduced Surface Charge
• Lower surface charge minimizes interaction with surfactants
-50
-40
-30
-20
-10
0
10
2 3 4 5 6 7 8 9 10
pH
ζ Po
tent
ial
ESNA1-LF
ESNA1
LFC1
Surface charge similar to LFC1
7
ESNA1-LF Salt Rejection(Surface water @ 13 gfd, 25 C)
83.8%
96.2% 96.4%
97.9%
89.9%
99.4%
85.6%
98.5%
75.0%
80.0%
85.0%
90.0%
95.0%
100.0%
Na Ca Mg Fe Cl SO4 SiO2 TOC
Feed Component Type
Rej
ectio
n (%
)
8
ESNA1-LF2: Salt Rejection(Surface Water @ 13 gfd, 25 C)
77.2%
93.5%95.0%
83.0%
92.5%
97.9%
75%
80%
85%
90%
95%
100%
Na Ca Fe Cl HCO3 SO4
Ion
Rej
ectio
n (%
)
9
Chemistry Modification of ESNA1Chemistry Modification of ESNA1--LF, LF, LF2 and LF3 to Achieve Desired LF2 and LF3 to Achieve Desired
Permeate HardnessPermeate HardnessHardness vs Iron Rejection
0
5
10
15
20
25
30
35
40
45
93 94 95 96 97 98 99
Membrane Nominal Calcium Rejection
Perm
eate
Cal
cium
(m
g/l a
s C
aCO
3)
0
0.05
0.1
0.15
0.2
0.25
0.3
Perm
eate
Iron
, mg/
l
Calcium pH=6.5 Calcium pH=7.0 Iron pH=6.5 Iron pH=7.0
ESNA1-LF
ESNA1-LF3
ESNA1-LF2
10
Typical Florida Feed Waters
11
Boca Raton Water Samples
12
ESNA1ESNA1--LF2 Pilot Data: Low Fouling LF2 Pilot Data: Low Fouling Membrane Performance ComparisonMembrane Performance Comparison
0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
0 5 10 15 20 25 30 35 40 45 50 55 60
Run Time (days)
Mas
s Tr
ansf
er C
oeff
icie
nt, M
TCw
(gfd
/psi
)
Membrane A ESNA LF
Feed TOC ~ 20 mg/LFeed TOC ~ 20 mg/L
Fouling of Stnd NF
Stable Performance of ESNA1-LF vs other NF
13
Deerfield Treatment Process
Holding Tank
5 um Cart Filters 769 gpm 322 gpmWell Waste
2145 gpm 1375 gpm 447 gpmProduct
Antiscalant Water25 C Acid RO System 1823 gpm482 ppm TDS ESNA1-LF Total250 ppm Hardness 85% Recovery 10.5 mgd285 ppm HCO3 5 Trains, 2 Stages1.5 ppm Fe 48 Vess x 24 Vess x 7 Elem20 ppm TOC 13 gfd Flux
14
City of Deerfield Beach, FL
RO System Design:10.5 MGD of PermeateESNA1-LF Membrane5 trains 48-24 array of 7M tubes 85% recovery13.0 gfd.
Pretreatment:AcidAntiscalantCartridge filtration.
Operation:Start-up November 2003Steady PerformanceNo cleaning in two years
15
Deerfield Beach Separation Objective
16
Deerfield Plant DataESNA1-LF Performance Trend
* Estimated from Conductivity
17
Salt Passage
0.001.002.003.004.005.006.007.008.009.00
10.0011.0012.00
12/03
/033/1
9/04
5/2/04
6/25/0
48/2
1/04
10/26
/0412
/1/04
1/7/05
2/8/05
3/11/0
54/1
3/05
5/12/0
56/1
4/05
7/22/0
59/1
/0510
/22/05
12/28
/052/2
1/06
3/24/0
6%
Skid 1 Stage 1ESNA1-LF Train 1Normalized Data
Deerfield Plant DataESNA1-LF Performance Trend
18
Deerfield Plant DataESNA1-LF Performance Trend
Salt Passage
0.001.002.003.004.005.006.007.008.009.00
10.0011.0012.00
12/03
/033/1
9/04
5/2/04
6/25/0
48/2
1/04
10/27
/0412
/1/04
1/7/05
2/8/05
3/11/0
54/1
3/05
5/12/0
56/1
4/05
7/22/0
59/1
/0510
/22/05
12/28
/052/2
1/06
3/24/0
6
Day
%
Skid 1 Stage 2ESNA1-LF Train 1Normalized Data
19
Deerfield Plant DataESNA1-LF Performance Trend
Perm Flow
0.00
200.00
400.00
600.00
800.00
1000.00
1200.00
1400.00
12/03
/033/1
9/04
5/2/04
6/25/0
48/2
1/04
10/26
/0412
/1/04
1/7/05
2/8/05
3/11/0
54/1
3/05
5/12/0
56/1
4/05
7/22/0
59/1
/0510
/22/05
12/28
/052/2
1/06
3/24/0
6
gpm
Skid 1 Stage 1ESNA1-LF Train 1Normalized Data
20
Deerfield Plant DataESNA1-LF Performance Trend
Perm Flow
050
100150200250300350400450500550600650700
12/03
/033/1
9/04
5/2/04
6/25/0
48/2
1/04
10/27
/0412
/1/04
1/7/05
2/8/05
3/11/0
54/1
3/05
5/12/0
56/1
4/05
7/22/0
59/1
/0510
/22/05
12/28
/052/2
1/06
3/24/0
6
Day
gpm
Skid 1 Stage 2ESNA1-LF Train 1Normalized Data
21
Deerfield Plant DataESNA1-LF Performance Trend
Differential Pres.
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
12/03
/033/1
9/04
5/2/04
6/25/0
48/2
1/04
10/26
/0412
/1/04
1/7/05
2/8/05
3/11/0
54/1
3/05
5/12/0
56/1
4/05
7/22/0
59/1
/0510
/22/05
12/28
/052/2
1/06
3/24/0
6
Day
psi
Skid 1 Stage 1ESNA1-LF Train 1Normalized Data
22
Boca Raton Treatment Process
Holding Tank
5 um Cart Filters 1136 gpm 450 gpmWell Waste
LSI = 1.9
3003 gpm 1867 gpm 686 gpmProductWater
25 C RO System 2553 gpm466 ppm TDS No Antiscalant ESNA1-LF2 Total265 ppm Hardness NO Acid 85% Recovery 40 mgd265 ppm HCO3 10 Trains, 2 Stages0.3 ppm Fe 72 Vess x 36 Vess x 7 Elem12 ppm TOC 12.2 gfd Flux
MediaFilter
23
City of Boca Raton, FLRO System DesignESNA1-LF2 (93% hrdnss rej)36.8 MGD permeate10 1st/2nd Stage Trains 72-36 array of 7M tubes85% recovery12.2 gfd
ESNA-LF3 (98% hrdnss rej)3.2 MGD permeate2 each 3rd Stage Trains36-18 array of 7M tubes50% recovery10.7 gfd
PretreatmentMulti-media
filters Cartridge filters No antiscalantNo acid addition
24
Boca Raton Separation Objective
25
Salt Passage
0
2
4
6
8
10
12
14
16
18
20
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
%Boca Raton Unit 7 Stage 1
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Nor
mal
ized
Sal
t Pas
sage
(%)
26
Salt Passage
0
3
6
9
12
15
18
21
24
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
%
Boca Raton Unit 7 Stage 2
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Nor
mal
ized
Sal
t Pas
sage
(%)
27
Perm Flow Norm.
0200400600800
100012001400160018002000220024002600
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
gpm
Boca Raton Unit 7 Stage 1
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Nor
mal
ized
Sys
tem
Flo
w (g
pm)
28
Perm Flow Norm.
0
50
100
150
200
250
300
350
400
450
500
550
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
gpm
Boca Raton Unit 7 Stage 2
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Nor
mal
ized
Sys
tem
Flo
w (g
pm)
29
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Differential Pres. Norm.
18
20
22
24
26
28
30
32
34
36
38
40
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
psi
Boca Raton Unit 7 Stage 1
Nor
mal
ized
Pre
ss D
rop
(psi
)
30
Boca Raton Plant DataESNA1-LF2/3 Performance Trend
Differential Pres. Norm.
10
12
14
16
18
20
22
24
26
9-Nov-04 17-Feb-05 28-May-05 5-Sep-05 14-Dec-05 24-Mar-06 2-Jul-06Date
psi
Boca Raton Unit 7 Stage 2
Nor
mal
ized
Pre
ss D
rop
(psi
)
31
Analysis of Fouled Membrane from Lead Element
SEM of Membrane Surface covered with foulant. 3000X
8.7N42.7C0.32Si0.8Fe
2229.8O5.55.9P8.28.2Ca
Ca3(PO4)2Atomic %Ion
EDAX of Membrane Surface covered with
foulant.
32
Boca Raton Plant DataPerformance Results
33
Conclusions
• Novel NF membrane chemistry allows controlled variation of the hardness rejection
• Modification of the surface results in a smoother, less charged surface which reduces fouling
• High rejection of NOM materials results in low disinfection by-products and meets Federal standards