Reverse Osmosis

Presented by
Dick Youmans, CWT
David H. Paul, Inc.

2
 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).

4
 Osmosis

Time = Zero Equilibrium Time

Less
Concentrated Pure Concentrated
Solution Solution Pure
Water
Water

5
Osmosis

6
 Osmosis

Time = Zero Equilibrium Time

Less
Concentrated Pure Concentrated
Solution Solution Pure
Water
Water

7
Types of Pressures Involved
1) Osmotic Pressure
2) Applied Pressures
A) Hydrostatic or Head
Pressure
B) Pump or External
Pressure
3) Net Driving Pressure
8
 Osmotic Pressure
Time = Zero Equilibrium Time

<1000
ppm
1000 Pure
ppm TDS TDS Pure
Water
Water

Osmotic
Pressure
10 psi

9
 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)
10
 Net Osmotic Pressure
Time = Zero Equilibrium Time

1000 1000 1000 1000

ppm ppm
ppm ppm
TDS TDS
TDS TDS

Osmotic
Pressure
10 psi
10 psi
11
Net Osmotic Pressure is 0 psi
 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 No
1 psi Change
1 psi
Net Pressure is 0 psi 12
 Applied Pressure
Time = Zero Equilibrium Time

4.6 feet
Pure Water 3.45 feet 3.45 feet
2.3 feet Pure Pure
Water Water
Pure Water

Hydrostatic Pressure Hydrostatic Pressure

1 psi 1.5 psi

2 psi 1.5 psi

Net Pressure is 1 psi Net Pressure is 0 psi

13
 Osmosis Stopped
Time = Zero Equilibrium Time
7 psi 7 psi

1000 300 ppm 1000 ppm 300 ppm

ppm 2.3 feet
TDS TDS TDS
TDS

Osmotic Pressure 3 psi 10 psi

Applied Pressure 8 psi 1 psi
Totals 11 psi 11 psi
Net Driving Pressure 0 psi 14
 Reverse Osmosis
Time = Zero Equilibrium Time
100 psi

1000 300
ppm 2.3 feet
ppm
TDS
TDS

Osmotic Pressure 3 psi 10 psi

Applied Pressure 101 psi 1 psi
Totals 104 psi 11 psi
Net Driving Pressure 93 psi 15
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.
16
 Definition of
Net Driving Pressure
Reverse Osmosis Unit
Feed Water 3 4 Permeate Flow

Flow 80 GPM

100 GPM 1 2
Concentrate Flow
20 GPM
NDP = Feed Water Pressure (1) + Osmotic
Pressure of Permeate (3) - Permeate Back
Pressure (4) - Osmotic Pressure of Feed
Water (2) 17
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
18
Spiral Wound RO Membrane Element

19
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
20
 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 21
 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 22
How Do RO Membranes Reject

Three Modes of Rejection

1) Ionic Charge
2) Molecular Weight
3) Physical Size

23
Rolling Your Own Reverse Osmosis
Membrane Element

24
Materials Needed

25
Fold Membrane in Two With 1/2 Inch Difference. Insert
the Permeate Carrier

26
To Simulate Glue Lines, Tape the Edges of the
Folded Sheet to Form the Envelope or “ Leaf ”.

27
Tape Permeate Tube to “ Leaf “, Lay Feed Water
Spacer on Top and Roll Your Element

28
Continue Rolling Until Finished

29
Pick a Colored Tape and Wrap a Shell
Around Your Element

30
Install the Brine Seal & Your Done.

31
Reverse Osmosis Membrane Element

32
 Reverse Osmosis
Water Flow Definitions

Permeate Flow Out

Feed Water In
Concentrate Flow Out

33
 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

34
 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

35
 Reverse Osmosis
Typical Residential Well Water Installation
Well Water

Cloth Filter

Carbon Filter

Drinking Water
Reverse
Osmosis
Concentrate
36
 Reverse Osmosis
Putting Elements into a Pressure Vessel
Pressure Vessel Inter-connectors Permeate Out

Element Element Element Element

Feed Concentrate
Water Brine Out
In Seals

37
 Reverse Osmosis
What is a Pressure Vessel?

38
 Reverse Osmosis
Putting Elements into a Pressure Vessel
Pressure Vessel Inter-connectors Permeate Out

Element Element Element Element

Feed Concentrate
Water Brine Out
In Seals

39
Water Flow Through Pressure Vessels
Feed Water

*Concentrate to Drain*
40
Permeate to Storage
 Concentrate Waste Disposal in the United States

Evaporation Zero Liquid

Ponds, 2% Discharge, 0%
Spray Irrigation, Deep Well
2% Injection, 9%

Discharge to Surface Water

Sewer, 42% Discharge, 45%

Source: Concentrate Disposal, by Irving Moch, Jr.

AMTA’s Pretreatment Solutions, Winter 2006/2007 41
 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
195 TDS

1st Stage 2nd Stage 43

Two Stage Reverse Osmosis Unit
(75% Recovery on a 6 - 3 Array)

2nd Stage

1st Stage

44
 Two Stage Reverse Osmosis Unit
(75% Recovery on a 30 - 15 Array)
2nd Stage 1st Stage

45
 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
46
Two Pass Reverse Osmosis Unit

47
Two Pass Reverse Osmosis Units

1) Booster Pump Between Passes

2) Storage Tank Between Passes

3) Caustic Soda Feed Between Passes

48
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

49
Hopefully, Time for Questions

Thank You,

Dick Youmans, CWT

50