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Ground Water Applications of MembranesMarch 30, 2011

Presented by:Bill Legge, P.Eng.GE Water & Process TechnologiesZENON Membrane Solutions

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Outline

• Overview • Common applica tions• Treatment requirements• Process design• Case studies

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Membrane Basics

How do membranes work?

Contaminants such as bacteria and viruses can not pass through the membrane’s pores

Water molecules and dissolved salts pass freely through the membrane pores

Semi permeable membrane wall with microscopic pores

Types of MembranesLow PressureMF & UF Removes:

Turbidity

Viruses

Bacteria

Protozoa

• Organics

High Pressure

NF & RO Removes:

Turbidity

Inorganics

Virus

Bacteria

Protozoa

Organics

Microfiltration(MF)

Ultrafiltration(UF)

Nanofiltration(NF)

Reverse Osmosis(RO)

Smallest Pore Size

Removal • Partial RemovalLegend

Turbidity and Microorganism Removal

Nominal pore size = 0.02 - 0.04 µm

Absolute pore size = 0.10 µm

Non-specific removal of: turbidity, bacteria , viruses by size exclusion

Cryptosporidium Parvum (4-7 µm) Giardia Lamblia (6-16 µm)

Unsupported immersed Ideal for large scale

potable, tertiary, desalination pre-treatment , and media filter retro-fit

Reinforced immersed Challenging raw water

quality MBR

500 Series 1000 Series 1500 Series

Unsupported pressurized Ideal for small scale

potable, tertiary, and desalination pre-treatment applications

Ideal for industrial process water, make-up and reuse applications

GE Ultrafiltration Membranes

Membrane Modulesare inserted into frames to form a Membrane Casset te

Membrane Casset tes are inserted into concrete tanks to form a Membrane Train

ZeeWeed® 1000 – Building Block Design

Air Compressorsand Air Dryer

Process Pumps

CIP Tank

Backpulse Tank

CIP Pumps

BlowersAir Compressors

Cleaning Chemicals

Membrane Tanks

Process Pumps

Typica l Immersed Configura tionPlan View

Future Tra in

5 (6) tra ins6 x 60 module cassettes16 (20) MGD

Overall dimensions:~ 45’ x 155‘

Immersed Operating Modes

PERMEATION MODE• Water passes through the membrane• Particles larger than the pore size of membrane are rejected• Particles accumulate in the tank

BACKWASH MODEPerformed when recovery reaches setpoint to remove solids from tank

• Reverse flow of treated water or ‘backpulse’• Aeration• Drain the tank and refill

Permeation and BackwashingPermeation~30-90 minutes< 5 minutes

Backwash

Raw Water

•a ir scour•backpulse• tank dra in• refill

•permeate down

Treated Water

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Applica tions in Groundwater Trea tment

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Common Membrane Applica tions

• Iron and manganese removal

• Arsenic removal

• Pre-trea tment to NF/RO

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Membranes for Iron & Manganese Removal

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Why remove iron & manganese

Iron:produces undesirable colour & tastesta ins laundry and plumbing reddish brownpromotes growth of iron bacteria

Manganese:produces undesirable colour & tastesta ins laundry and plumbing blackleads to accumula tion of microbia l growths

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How much iron & manganese to remove

• In most jurisdictions, the following aesthetic objectives apply for drinking water

• Iron ≤ 0.3 mg/L

• Manganese ≤ 0.05 mg/L

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Chemistry of Oxida tion

• Under reducing conditions such as GW, both Iron and Manganese can be present in dissolved form

• Dissolved iron and manganese cannot be removed by a UF/MF membrane as they a re smaller than the pore size of the membrane

• Addition of oxidant converts dissolved Iron and Mninto precipita tes which can be removed by UF/MF membranes

Fe (II) (soluble) Fe(OH)3 (Insoluble)Mn (II) (soluble) MnO2 (Insoluble)

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Chemistry of Oxida tion

• Iron is rela tively easier to oxidize and can be oxidized by aera tion under most circumstances

• Manganese is more difficult to oxidize and requires a stronger oxidizing agent such as potassium permanganate.

• Oxida tion efficiency improves with increase in pH

• Waters with low pH may require some base addition

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Oxida tion + membrane filtra tion

Air

PermeatePump

Reject

Contact Chamber(optional)

Flash Mixer

Oxidant

Feed

pH Adjustment(optional)

Air

UF/MF Membrane

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Case Study: Seekonk, MA

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Seekonk, MA – Trea tment objectives

High iron and manganese levels exceeding objectives

Parameters Raw Water Treated Water UnitsTurbidity < 2.0 <0.1 NTUIron 0.06 – 0.2 <0.1 mg/LManganese 2.5 – 3.5 <0.03 mg/L

Temperature 0.5 - 25 oC

pH 7.0 – 8.5

Alkalinity 95 - 108 mg/L as CaCO3

Hardness 92 - 124 mg/L as CaCO3

Giardia >4 log removalCryptosporidium >4 log removal

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Seekonk, MA – Oxidation + UF

PermeatePump

Reject

Flash Mixer

KMnO4NaOH

Feed

Air

4.3 mgd

FeedPumps

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Seekonk, MA – Immersed UF Tanks

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Seekonk, MA - Iron removal

0

0.02

0.04

0.06

0.08

0.1

0.12

26-Mar 31-Mar 5-Apr 10-Apr 15-Apr 20-Apr 25-Apr 30-Apr 5-May

Tota

l Iro

n (m

g/L)

Raw Water Permeate

Removal Objective: 0.1 mg/L

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Seekonk, MA - Manganese removal

0.001

0.01

0.1

1

10

26-Mar 31-Mar 5-Apr 10-Apr 15-Apr 20-Apr 25-Apr 30-Apr 5-May

Tota

l Man

gane

se (m

g/L)

Raw Water Permeate

Removal Objective: 0.03 mg/L

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Membranes for a rsenic removal

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Arsenic Removal

• Arsenic is a carcinogen and has other hea lth effects such as cardiovascular disease, diabetes, and neurologica l effects

• USEPA’s Primary Drinking Water Regula tion requires a Maximum Contaminant Level (MCL) of 0.010 mg/L

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Chemistry of Oxidation/Coagula tion

• Under reducing conditions, such as GW, arsenic is predominantly present as the triva lent species arsenite As(III) as opposed to arsenate As(V)

• As(III) and As(V) are soluble and cannot be removed by a UF/MF membrane as they are smaller than the pore size of the membrane

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Chemistry of Oxidation/Coagula tion

• As(III) must be oxidized to As(V) as As(V) is more readily removed by coagula tion

• Oxidation can be achieved using an oxidant such as potassium permanganate

• As(V) is then adsorbed onto ferric hydroxide floc for removal by a UF/MF membrane

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Arsenic Removal

Feed Water

RejectAir

PermeatePump

FlocculationChamber

(5 min HRT)

KMnO4Cl2ClO2

Flash Mixer

As 3+ , As 5+

FeCl3

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Case Study: Scottsda le, AZ

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Arsenic RemovalChaparra l WTP, Scottsdale, AZ – 30 MGDZeeWeed® 500

Overview

•Treatment for DOC and arsenic removal

•Commissioned Fall 2006

•Ferric chloride (15-20 mg/L)

•GAC downstream for geosmin, MIB and THM precursor removal

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Arsenic removalScottsdale, AZ Pilot #1 - Arsenic Removal

0

5

10

15

20

25

30

35

40

15-Jul 12-Aug 9-Sep 7-Oct 4-Nov 2-Dec

Arse

nic

Conc

entr

atio

n (u

g/L)

feed - natural As feed - spiked As(V) feed - spiked As (III) permeate

5 mg/L 10 mg/L0 mg/L 15 mg/L

MDL = 1 ug/L

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Membranes for NF/RO pre-trea tment

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Why use NF/RO

For groundwaters conta ining high levels of dissolved sa lts or organics:

tota l dissolved solidsnitra tessulphatessodiumorganics

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RO vs. NF

Reverse Osmosis Membrane

8” dia. x 40” long

Design same as NF

Components same as NF

Operation same as NF

(200 – 250 psi)

99.7% salt rejection

Nanofilt rat ion Membrane

8” dia. x 40” long

Design same as RO

Components same as RO

Operation same as RO

(90 – 120 psi)

95 – 96% rejection divalent ions (Ca, SO4)

50 – 60% rejection monovalent ions (Na, Cl)

“LooseRO”

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Spira l Wound Membrane

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Reliable Pretrea tment is Critica l

High ra te of fouling

High frequency of cleaning

Lower recovery ra tes

High opera ting pressure

Poor product quality

Reduced membrane / resin life

Reduced plant productivity

Spira l wound membranes are sensitive and require a continuous supply of high quality water

Ineffective pretrea tment can result in:

Bacteria, mineral salts and silt on a SDI filter paper

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Typica l Potable Water Flowsheet

UF/MF

Blend

NF/RO

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UF/MFAdvantages for Pretrea tment

• Positive barrier to particula tes and colloida l particles – no breakthrough

• Significantly reduced fouling and cleaning frequency and extended NF/RO membrane life

• Reliable production of high qua lity water• Higher NF/RO flux• Smaller footprints• Lower chemica l requirements

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Conclusion

• Membranes are exceptional for turbidity and pathogen removal.

• With appropria te pretrea tment, membranes are effective in removing Fe, Mn, As

• UF/MF membranes as pre-trea tment to the NF/RO, effective for removal of dissolved contaminants

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Questions