Reverse Osmosis
Presented by
Dick Youmans, CWT
David H. Paul, Inc.
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Outline for this Presentation
1)
Define Osmosis and Reverse Osmosis
2)
Types of Membranes and Their Characteristics
3)
Manufacturing Process for the “Membrane”
4)
Demonstration: Rolling One Of Our Own
5)
Understand Water Flow Through an Element
6)
Understand Water Flow Through Pressure Vessels
3
Definition of Osmosis
Osmosis is the process where a solvent
(usually water) passes from a dilute
solution into a more concentrated one by
moving through a semipermeable
membrane which selectively allows the
passage of the solvent, but restricts the
passage of the solute (dissolved solids).
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Osmosis
Time = Zero
Equilibrium Time
Less
Concentrated
Pure
Concentrated
Solution
Water
Solution
Pure
Water
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Osmosis
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Osmosis
Time = Zero
Equilibrium Time
Less
Concentrated
Pure
Concentrated
Solution
Water
Solution
Pure
Water
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Types of Pressures Involved
1) Osmotic Pressure
2) Applied Pressures
A) Hydrostatic or Head
Pressure
B) Pump or External
Pressure
3) Net Driving Pressure
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Osmotic Pressure
Time = Zero
Equilibrium Time
<1000
ppm
1000
ppm TDS
Pure
Water
TDS
Pure
Water
Osmotic
Pressure
10 psi
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Approximate Osmotic Pressures
• TDS in ppm
• Osmotic Pressure in psi (bar)
100 ppm
1 psi (.069Bar)
1,000 ppm
10 psi (.69 Bar)
5,000 ppm
50 psi (3.45 Bar)
10,000 ppm
100 psi 6.9 Bar)
15,000 ppm
150 psi (10.35 Bar)
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Net Osmotic Pressure
Time = Zero
1000
ppm
1000
ppm
TDS
TDS
Equilibrium Time
1000
1000
ppm
ppm
TDS
TDS
Osmotic
Pressure
10 psi
10 psi
Net Osmotic Pressure is 0 psi
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Applied Pressure
Time = Zero
Equilibrium Time
2.3 feet
2.3 feet
2.3 feet
2.3 feet
Pure Water
Pure Water
Pure Water
Pure Water
Hydrostatic Pressure
1 psi
No
Change
1 psi
Net Pressure is 0 psi
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Applied Pressure
Time = Zero
Equilibrium Time
4.6 feet
Pure Water
2.3 feet
Pure Water
3.45 feet
3.45 feet
Pure
Water
Pure
Water
Hydrostatic Pressure
Hydrostatic Pressure
1 psi
1.5 psi
2 psi
Net Pressure is 1 psi
1.5 psi
Net Pressure is 0 psi
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Osmosis Stopped
Time = Zero
Equilibrium Time
7 psi
1000
ppm
7 psi
300 ppm
TDS
1000 ppm
2.3 feet
300 ppm
TDS
TDS
Osmotic Pressure
3 psi
10 psi
Applied Pressure
8 psi
1 psi
11 psi
11 psi
TDS
Totals
Net Driving Pressure
0 psi
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Reverse Osmosis
Equilibrium Time
Time = Zero
100 psi
1000
ppm
TDS
300
ppm
2.3 feet
TDS
Osmotic Pressure
3 psi
10 psi
Applied Pressure
101 psi
1 psi
Totals
104 psi
11 psi
Net Driving Pressure
93 psi
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Definition of Reverse Osmosis
Reverse Osmosis occurs when
sufficient external pump pressure is
applied to the more concentrated
solution to overcome osmotic and
hydrostatic pressures to reverse the
osmotic reaction causing water to
flow from the concentrated solution
to the dilute solution.
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Definition of
Net Driving Pressure
Reverse Osmosis Unit
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Feed Water
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Permeate Flow
80 GPM
Flow
100 GPM
1
2
Concentrate Flow
NDP = Feed Water Pressure (1) + Osmotic
Pressure of Permeate (3) - Permeate Back
Pressure (4) - Osmotic Pressure of Feed
Water (2)
20 GPM
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Major Types of Membranes Configurations
1) Tubular (inside out)
2) Hollow Fiber (outside in)
a) Shell & Tube Heat Exchanger
3) Spiral Wound
a) Cellulose Acetate
b) Thin Film Polyamide Composite
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Spiral Wound RO Membrane Element
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Cellulose Acetate Membranes
1) More Expensive than Thin Film
Membranes
2) Typical salt rejection of 96%
3) Typical operating pressures of 400
to 700 PSI
4) Optimum pH operating range of 4.8
to 6.5
5) Good Chlorine Tolerance
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Thin Film Composite Membranes
1) Less expensive than cellulose acetate
membranes
2) Typical salt rejection of 97 to 98%
3) Typical operating pressures of 200 - 300 PSI
4) Wide pH operating range of 2 - 10
5) Very Low Chlorine Tolerance
6) Less susceptible to compaction due to lower
PSI
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Reverse Osmosis Membrane
Sheet Components
Cellulose Acetate Membrane
(Asymmetric)
Dense Skin
Porous Support
Backing Material
Thin Film Composite Membrane
Semipermeable Membrane
Porous Support
Backing Material
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How Do RO Membranes Reject
Three Modes of Rejection
1) Ionic Charge
2) Molecular Weight
3) Physical Size
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Rolling Your Own Reverse Osmosis
Membrane Element
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Materials Needed
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Fold Membrane in Two With 1/2 Inch Difference. Insert
the Permeate Carrier
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To Simulate Glue Lines, Tape the Edges of the
Folded Sheet to Form the Envelope or “ Leaf ”.
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Tape Permeate Tube to “ Leaf “, Lay Feed Water
Spacer on Top and Roll Your Element
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Continue Rolling Until Finished
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Pick a Colored Tape and Wrap a Shell
Around Your Element
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Install the Brine Seal & Your Done.
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Reverse Osmosis Membrane Element
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Reverse Osmosis
Water Flow Definitions
Permeate Flow Out
Feed Water In
Concentrate Flow Out
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Reverse Osmosis
Versus Traditional Filtration
1) Filtration
Water Flow in
Water Flow out
2) Reverse Osmosis (Cross Flow Filtration)
Permeate Flow Out
Water Flow In
Concentrate Flow Out
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Does Reverse Osmosis
Require Pretreatment?
1) Settling Basins for Silt & Mud
2) Filtration for suspended solids
3) Ion Exchange for Hardness Salts
4) Demineralization for Anions & Cations
5) Activated Carbon Filters for Organics
Permeate Quality Required Dictates Pretreatment
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Reverse Osmosis
Typical Residential Well Water Installation
Well Water
Cloth Filter
Carbon Filter
Reverse
Osmosis
Drinking Water
Concentrate
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Reverse Osmosis
Putting Elements into a Pressure Vessel
Pressure Vessel
Element
Feed
Water
In
Inter-connectors
Permeate Out
Element
Element
Brine
Seals
Element
Concentrate
Out
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Reverse Osmosis
What is a Pressure Vessel?
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Reverse Osmosis
Putting Elements into a Pressure Vessel
Pressure Vessel
Element
Feed
Water
In
Inter-connectors
Permeate Out
Element
Element
Brine
Seals
Element
Concentrate
Out
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Water Flow Through Pressure Vessels
Feed Water
*Concentrate to Drain*
Permeate to Storage
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Concentrate Waste Disposal in the United States
Evaporation
Ponds, 2%
Spray Irrigation,
2%
Zero Liquid
Discharge, 0%
Deep Well
Injection, 9%
Discharge to
Sewer, 42%
Source: Concentrate Disposal, by Irving Moch, Jr.
AMTA’s Pretreatment Solutions, Winter 2006/2007
Surface Water
Discharge, 45%
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Single Stage Reverse Osmosis Unit
(50% Recovery)
Permeate 50 GPM
Feed
100
GPM
Concentrate 50 GPM
42
Two Stage Reverse Osmosis Unit
(75% Recovery on a 4 -2 Array)
50 GPM
75 GPM
5 TDS
6.7 TDS
25 GPM
10 TDS
100
GPM
100
TDS
25 GPM
380 TDS
50 GPM
1st Stage
195 TDS
2nd Stage
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Two Stage Reverse Osmosis Unit
(75% Recovery on a 6 - 3 Array)
2nd Stage
1st Stage
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Two Stage Reverse Osmosis Unit
(75% Recovery on a 30 - 15 Array)
2nd Stage 1st Stage
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Two Pass Reverse Osmosis Unit
(25% Recovery )
50 GPM
25 GPM
5 TDS
0.25 TDS
100 GPM
100 TDS
25 GPM
10 TDS
50 GPM
195 TDS
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Two Pass Reverse Osmosis Unit
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Two Pass Reverse Osmosis Units
1) Booster Pump Between Passes
2) Storage Tank Between Passes
3) Caustic Soda Feed Between Passes
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Two Pass / Two Stage Reverse Osmosis Unit
4 -2 Array 1st Pass / 2 – 1 Array 2nd Pass
1st Pass 2nd Pass
2nd Stage
2nd Stage
1st Stage
1st Stage
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Hopefully, Time for Questions
Thank You,
Dick Youmans, CWT
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