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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
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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