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 Pure Solution Water Solution Water
5 Osmosis
6 Osmosis
Time = Zero Equilibrium Time
Less Concentrated Pure Concentrated Pure Solution Water Solution 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 Net Osmotic Pressure is 0 psi 11 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 0 psi Net Pressure is 1 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
NDP = Feed Water Pressure (1) + Osmotic 20 GPM 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 Pretreatment35 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