novel low fouling nanofiltration membranes · 2019-01-07 · nanofiltration permeate hardness had...

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


18


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

%


19


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


20


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


21


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


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


%

Boca Raton Unit 7 Stage 2


Nor

mal

ized

Sal

t Pas

sage

(%)

27

Perm Flow Norm.

0200400600800

100012001400160018002000220024002600


gpm



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


gpm



Nor

mal

ized

Sys

tem

Flo

w (g

pm)

29


Differential Pres. Norm.

18

20

22

24

26

28

30

32

34

36

38

40


psi


Nor

mal

ized

Pre

ss D

rop

(psi

)

30


Differential Pres. Norm.

10

12

14

16

18

20

22

24

26


psi


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

novel low fouling nanofiltration membranes · 2019-01-07 · nanofiltration permeate hardness had...

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