Michael Bourke – Wigen Water Technologies

www.wigen.com

Potable Applications of NF/ROAesthetic

TDSHardnessSulfateColor

RegulatoryNitrateArsenicRadionuclidesFluorideSeleniumPesticidesHeavy Metals

Contaminant Removal Rates using RO & NF

Comparative Removal Rates NF RO

Monovalent Ions (Sodium, Potassium, Chloride, Nitrate, etc) <50% >98%

Divalent Ions (Calcium, Magnesium, Sulfate, Carbonate, Iron, etc)

>90% >99%

Microsolutes (<100 Mw) 0-50% 0-99%

Microsolutes (>100 Mw) >50% >90%

Feed Water

Membrane

Permeate

Concentrate

Pressure

Membrane separation is a process in which properly pretreated source water is delivered at moderate pressures against a semipermeable membrane. The

membrane rejects most solute ions and molecules, while allowing water of very low mineral content to pass through.

Feed Water

Concentrate

Permeate Membrane Material

Spacer Material

Permeate Carrier Material

The most common RO membrane material today is aromatic polyamide, typically in the form of thin-film composites. They consist of a thin film of membrane bonded to layers of other porous materials that are tightly wound to support and strengthen the

membrane.

NF/RO Membrane Operation

NF/RO System Components

1. Feed water characteristics- Cations- Anions- Silt Density Index (SDI)- Temperature- Oxidants

2. Pre-treatment requirements

- Mechanical and/or chemical- Solids removal (turbidity < 1 NTU)- Fe/Mn removal- Anti-scalant and sodium bisulfite dosing

3. Determine desired permeate quality & flow- Membrane selection- Recovery achievable/waste volume- Amount of bypass

4. O&M Requirements- Power & Pretreatment chemicals- Cartridge filter replacement- CIP Chemicals- Membrane Replacement

10-15% increase in normalized 10-15% increase in normalized differential pressuredifferential pressure

10-15% decrease in normalized 10-15% decrease in normalized permeate flowpermeate flow

10-15% decrease in permeate quality10-15% decrease in permeate quality

Prior to sanitizationPrior to sanitization

Regular Maintenance ScheduleRegular Maintenance Schedule

Every 3 to 12 monthsEvery 3 to 12 months

Cleaning Frequency?

Case StudiesCity of Wellman, IA

New RO System for Radium & Ammonia Removal and General Water Quality Improvement.

City of Creighton, NE Upgraded RO System to Improve Nitrate Removal.

• Background• Trial Objectives• Pilot Plant Selection• Results• Full-scale System Design

Wellman, Iowa

• Population ~1400• Groundwater supply• Greensand Filters• DW violations for:

- Nitrite- Combined radium

Raw Water Characteristics

Parameter Range (Ave)TDS, mg/L 1600 – 3620 (1914)

Ammonia, mg/L as N 0.2-4.2 (3.8)

Total Hardness, mg/L as CaCO3 780-1070

Sulfate, mg/L 91- 2230 (1219)

Combined Radium, pCi/L 2.0 – 21.3 (6.5)

Fluoride, mg/L 0.6 – 1.1

Silica, mg/L as SiO2 13 – 14

Iron, mg/L < 0.03 mg/L

Manganese, mg/L 0.006 – 0.055

Chloride, mg/L 6.5 – 85.6

Sodium, mg/L 150 - 764

TOC, mg/L 1.3 – 1.8

Trial Objectives

Three month trial required by IA DNR.Demonstrate RO system performance on a pilot

plant representative of a full-scale system.

Parameter (actual) Target

Combined Radium (2.0-21.3)

< 5.0 pCi/L*

Sulfate (910-2230) < 250 mg/L#

TDS (1600-3620) < 500 mg/L#

Hardness (780-1070) < 250 mg/L as CaCO3

Ammonia (0.2-4.2) As low as possible*EPA Primary DW Regulation#EPA Secondary DW Regulation

Pilot CriteriaRepresentative of Full-scale Design

Average flux ratesArray Length (6L) – representative flux per

elementMembrane element diameter/type

Representative Pre-treatmentFiltrationFe/Mn RemovalChemical Dosing

Representative Feed Water

Pilot Plant Set-up

S1 Feed(elements 1-3)

S1 Feed(elements 4-6)

S2 Feed

Concentrate

2-2:1-1, 3-Long Pilot Plant, Simulates 2:1, 6-Long System

Trial DesignDuration – cover minimum CIP frequencyData Collection

Automatic (pressure, flows, conductivity, temperature)

Normalized data to monitor system performance, early signs of fouling or membrane damage.

Manual (feed, permeate & concentrate samples)Membrane Autopsy

Detect/identify cause of fouling (lead and end elements)

Takes changes in pressure and temperature and then normalizes, or adjusts, the recorded permeate flow rate accordingly.

Data Normalization

Graphically shows the permeate flow rate without the effects temperature

Indicates the need for cleaning Helps troubleshoot system

System Flows vs. Time

3.00

8.00

13.00

18.00

26-Jun-09 06-Jul-09 16-Jul-09 26-Jul-09 05-Aug-09 15-Aug-09 25-Aug-09 04-Sep-09 14-Sep-09 24-Sep-09 04-Oct-09

Date

Flo

w (

gp

m)

Normalized Permeate Flow Permeate Flow Concentrate Flow Linear (Normalized Permeate Flow)

No decrease = minimal fouling

Potential MembraneDamage

Normalized Permeate Conductivity vs. Time

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

26-Jun-09 06-Jul-09 16-Jul-09 26-Jul-09 05-Aug-09 15-Aug-09 25-Aug-09 04-Sep-09 14-Sep-09 24-Sep-09 04-Oct-09

Date

No

rma

lize

d P

erm

ea

te C

on

du

cti

vit

y (

uS

/cm

)

Normalized Permeate Conductivity (uS/cm) Permeate Conductivity

Linear (Normalized Permeate Conductivity (uS/cm))

CIP Performed

TDS vs. Time

0

500

1000

1500

2000

7/14

7/21

7/28 8/4

8/11

8/18

8/25 9/1

9/8

9/15

9/22

9/29

Date

TD

S (

mg

/l)

Feed TDS

Permeate TDS

• 98.9% TDS Reduction• 16-28 mg/L

Hardness vs. Time

0

100

200

300

400

500

600

700

800

900

1000

7/14

7/21

7/28 8/4

8/11

8/18

8/25 9/1

9/8

9/15

9/22

9/29

Date

Har

dn

ess

(m

g/la

s C

aCO

3)

Feed Hardness

Permeate Hardness

• 99.9% Hardness Reduction• 0.9-2.0 mg/L as CaCO3

(slight increase in last week)

Sulfate vs. Time

0

200

400

600

800

1000

1200

1400

7/14

7/21

7/28 8/4

8/11

8/18

8/25 9/1

9/8

9/15

9/22

9/29

Date

Su

lfat

e (

mg

/l)

Feed Sulfate

Permeate Sulfate

Ammonia vs. Time

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

7/14

7/21

7/28 8/4

8/11

8/18

8/25 9/1

9/8

9/15

9/22

9/29

Date

Am

mo

nia

(m

g/l

as N

)

Feed Ammonia

Permeate Ammonia

• 99.94% Sulfate Reduction• 0.9-4.2 mg/L (slight increase

in last week)

• Below detection (<0.09 mg/L)

•First membrane in bank 1 and last in bank 2

•No visible signs of fouling.

•∆P and Flowrate within acceptable ranges

•Conductivity rejections of 97.3% & 97.1% below spec of 99.5% - possible chlorine damage.

•Fujiwara test was positive for halogen on membranes indicating oxidative attack.

• TDS, sulfate, hardness & ammonia reduced to well below targets.

• Combined radium (226/228) reduced to below detection <1.0 pCi/L (feed levels only ~2.0 pCi/L during trial).

• Increase in permeate flow and some salts determined to be due to chlorine oxidation. Possible chlorine peaks in feed or loss of sodium bisulfite dosing.

• No fouling experienced over trial period with 2.3 mg/L dose of Vitec 3000, and CIP frequency likely to be every 4-6 months.

• Two x 100 gpm RO skids

• 20% Bypass stream

• Design flux of 14.4 GFD & 75% recovery

• Array: 3:1, 6-Long

• Toray TMG20-400 membranes

• ORP meter on feed to shut down RO on detection of Cl2 residual.

• Waste to sewer.

July 2011

• Background• RO System Capabilities for NO3

Removal & Factors Impacting Performance

• Overhaul of City’s RO System• System Performance – Before & After

City of Creighton• Population ~1200• Groundwater supply• Raw Water Nitrate 15-20 mg/L

RO System History – First in NEInstalled in 1993 – first

RO system in Nebraska

Two skids each with two RO trains.

Array per RO train:3:2, 6-long

Feed: 130 gpm per train

Permeate: 100 gpm per train (76% recovery)

RO Concentrate120 gpm

RO Train 4

Greensand Filters

RO Train 3

RO Train 2

RO Train 1

Well Pumps

Bypass – 125 gpm

Finished Water 525 gpm

Permeate 400 gpm

RO System HistoryBypass: 50% reduced to 25% with increasing

raw water nitrate levels to stay in compliance.Trains 1 & 2 historically had significantly

more use:Membranes replaced most recently in 1 & 2

due to greater TDS and nitrate leakage.No improvement in Train 1 and 2

performance after membrane replacement.System placed on compliance order in early

2011 – given 90 days to get in compliance.

Projection conducted for Toray TMG20N-400C low energy RO membranes.

With 20 mg/L NO3-N in feed, theoretical permeate level was 1.67 mg/L.

Nitrate from trains 1 & 2 was >5.0 mg/L.Determined that reconditioned RO

membranes had been recently installed in trains 1 and 2.Typically used for hardness removalNot suitable for nitrate removal

Projection ResultsParameter Raw Feed PermeateNitrate, mg/L as N 20 1.67 (actual ~5.5)

Hardness, mg/L as CaCO3 223 2.5

Sulfate, mg/L 22 0.05

Calcium, mg/L 77 0.66

Magnesium, mg/L 12.9 0.11

Silica, mg/L as SiO2 13 0.21

Chloride, mg/L 10 0.04

Sodium, mg/L 15.3 0.17

TDS, mg/L 11.0 (actual ~140)

Contaminant Removal Rates using RO & NF

Comparative Removal Rates NF RO

Monovalent Ions (Sodium, Potassium, Chloride, Nitrate, etc) <50% >98%

Divalent Ions (Calcium, Magnesium, Sulfate, Carbonate, Iron, etc)

>90% >99%

Microsolutes (<100 Mw) 0-50% 0-99%

Microsolutes (>100 Mw) >50% >90%

Install Toray Low Energy Membranes (TMG20N-400C) in worst performing trains (1 & 2).

Fastest and lowest cost to get system back in compliance.

Future:Replace existing pumps with

more efficient low energy pumps.Replace membranes in trains 3 &

4.

Trains 1 & 2 Membranes Replaced

Trains 1 & 2 Membranes Replaced

Trains 1 & 2 Membranes Replaced

Previous RO Membranes:Operating Pressure: 150 psiPump Power: 20 HP per trainAnnual Power Cost*: $7,840 per train @ 10c/kWh

Low Energy RO Membranes:Operating Pressure: 110 psiPump Power: 15 HP per trainAnnual Power Cost*: $5,880 per train @ 10c/kWh

Annual Power Savings: $7,840 (25% reduction)

*Assuming 60% plant utilization

Operating Costs: c/1000 galPower 10.4Chemicals# & cartridge filters 14.9Membrane replacement (5 years) 16.5Total* 41.8

*Assuming 60% plant utilization, 75% recovery & 20% bypass.

#Bisulfite, antiscalant, CIP chemicals

• Determined that reconditioned membranes were not effectively removing nitrate and resulting in MCL violations.

• Replacement of train 1& 2 membranes immediately brought system back in to compliance.

• Low energy membranes will save City ~$8000 per year in pumping power.

• Don’t assume any RO membrane can remove >90% nitrate!

Questions?

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