1. Desalination by Reverse Osmosis
Leili Abkar

2. Why Desalination ?

3. Desalination Technology
Membrane
Electric
EDR
Pressure MF RO NF UF
Thermal
MSF
MED
TVC
Desalination : is a process that removes or separate salt from saline water. it produces fresh water at the expenses of energy consumption.
It is mainly classified in two groups : membrane and thermal desalination.
As you may know , thermal desalination uses heat to boil water and vaporize water then condensation of water give fresh water , main process are MED, TVC, and MSF .
Membrane desalination, uses a semi pre- meabale membrane to pass water across the membrane.

4. Pressure Driven MembraneMF
0.7 bar UF
1-7 bar NF
bar RO
7-69 bar
∆P=
Suspended particles can be removed by MF
Viroses can be removed by UF
MULTIPLE CHARGED IONS BY NF
SINGLE CHARGED IONS BY RO
Mid-size organic substances,
multiple charged ions
Bacteria, parasites, particles
High molecular substances( ions and proteins), viruses
Low molecular substances, single charged ions

5. Reverse Osmosis History
Dr. Sourirajan - 1962
Abbe Nollet -1748
Reverse Osmosis History

6. 1748 : Abbe Nollet observed the phenomenon of Osmosis
1994 : TriSep introduce first “low fouling” membrane,
1995 : Hydranautics introduces first “ energy saving” polyamide membrane,
2002: Koch Membrane System introduces first 18 inch diameter “MegaMagnum” module,

7. Year
Pressure (psi)
Relative Flux
Rejection (%)
Membrane Material
1970’s
435 1 97
Cellulose acetate
1980’s
290
1.9 99
Cross-linked polyamide composite
1987
220
3.0
99.7
Cross-linked aromatic polyamide composite
1988
145
4.2
1996
110
5.6
1999 75
8.0

8. Osmosis and Reverse Osmosis Phenomenon
Water with low concentration has higher chemical potential

9. Thin-film, composite membranes
RO Membrane Structure
RO membranes
Asymmetric membranes
Thin-film, composite membranes
Reverse osmosis membrane separations
Chemical nature of the membrane material (almost always a polymer)
Physical structure

10. RO Membrane Structure

11. Membrane Module Objective :
Pack large amount of membrane area into relatively small volume
Economical
Smaller footprint

12. Membrane Module Tubular Spiral wound Hollow fibre
Plate & frame
Tubular
Spiral wound
Hollow fibre
There are 4 basic forms of membrane modules :
Plate and frame : usually are used for high suspended solids , ad not in water purification . Consist of a flat sheet membrane , typically two membranes are placed back to back ; then stacked within a frame work for support and there are spacer placed between each plate keep them from sticking together and provide open channel for water to flow trough.
Tubular module : typically for high solids, found in the food and biological industries, resemble the heat exchanger shell and tube , with feed water in the tubes and permeate water in the shell.
Howllow fiber RO membrane formed in a very small diameter tubes, they resemble human hair and can be as flexible and flow of water is outside in , and the thin layer of RO membrane is on the outside of the membrane.

13. Membrane Module

14. How Does Reverse Osmosis Work ?

15. Performance Parameters
Salt rejection%
Salt passage %
Salt Rejection = Conductivity of Feed Water – Conductivity of Permeate Water Conductivity of Feed ×100
Salt Passage % = (1- Salt Rejection%)
How effective the RO membranes are removing contaminants
A well-designed RO system with properly functioning RO membranes will reject 95% to 99%

16. Performance Parameters
Recovery %
Recovery% = Permeate Flow Rate Feed Flow Rate ×100
The higher the recovery
Less water to drain as concentrate
Saving more permeate water
Recovery is too high
Scaling
Fouling
The % Recovery depends on
Feed water chemistry
RO pre‐treatment
Industrial RO runs anywhere between 50%- 85 %

17. Performance Parameters
Concentration Factor%
High concentration factor
High scaling potential
Brackish water
3,000 mg/L and CF=5
Brine Salinity = 3,000*5= 15,000 mg/L
Sea Water
35,000 mg/L and CF = 2
Brine Salinity = 35,000*2= 70,000 mg/L
Concentration Factor = 1 1−Recovery %
Recovery
Concentration factor
50% 2
75% 4
80% 5
83% 6
87.5% 8

18. Performance Parameters
Flux= Permeate Flow Rate # of RO elements in system x Surface area of each RO element
Flux
Feed Water Source
GFD
TDS (mg/L)
Sea Water
8-12
35,000
Brackish Surface Water
10-14
1,000-5,000
Brackish Well Water
14-18
5,000-15,000
RO Permeate Water
20-30
<1,000

19. Operating Condition TFC membrane pH = 2-11 Temperature < 45 C

20. How to Design RO System Manually
Calculate osmotic pressure of feed water
Directly related to operating pressure
Determine Silt Density Index (SDI)
Fouling indication
Must be < 5 to use membrane
Choose the proper membrane

21. Flux×Active Membrane Area Permeate water flow rate
No. Membrane
Flux×Active Membrane Area
Permeate water flow rate
No. Pressure Vessels
1-7
No. Membrane

22. Design Software

23. Different Design Passes Passes Stages

24. Different Design – 2 Stage

25. Water Treatment Plant

26. Minimum Required Water Quality Analysis
Source Water
Minimum Required Water Quality Analysis
Water quality and quantity
Historic data

27. Guideline for RO Feed Water
Pre-treatment
Objective :
Make the feed water compatible with RO membrane
Poor Pre-treatment:
Fouling
Biofouling
Scaling
Guideline for RO Feed Water

28. Pre-treatment Chemical Mechanical

29. Pre-treatment Example A:
Selection of pretreatment may impact post treatment. A good example would be if acid is used to lower the pH of the feed water (for reducing scaling potential), the carbonate will convert to the CO2 which may need to be removed with a degasifier process in the post treatment.
Example B:
If chlorination is used to control microbiological growth in the pretreatment, overfeeding will cause degradation of Thin-Film Composite RO elements.

30. Pre-treatment Sufficient pre-treatment Conclusion
Membrane cleaning 3-4 times per year
Membrane life last over 5 years
Conclusion
No single solution for pre-treatment,
Depends on source water quality, seasonal and historical changes

31. Post treatment Choice and sequence of post treatment Objective :
Make the permeate water compatible with distribution system
Post-treatment
Stabilization,
Disinfection,
Corrosion control,
Degasification and/or air stripping processes
Carbon dioxide and hydrogen sulfide gases
Choice and sequence of post treatment
Regulatory requirements,
The design of the system,
Finished water quality criteria,
Water chemistry

32. Membrane Desalination Cost

33. Membrane Desalination Cost
1. Price includes all costs to consumers for treatment
and delivery.
2. Cost is based on a family of four using 100 gallons
per day per person, for a total monthly use of
12,000 gallons. Cost is based on the average of the
“To Consumer” cost shown.
3. Brackish is moderately salty-1,000-5,000mg/L
total dissolved solids (TDS).
4. Seawater contains 30,000-35,000mg/L TDS.
5. Cost is for typical urban coastal community in the
USA. Costs for inland communities may be higher.
6. Combined supply costs are for the traditional supply
augmented with 50% of desalted brackish water, or
10%. of desalted seawater.

34. Largest SWRO Desalination Plant - 2013
Sorek Desalination plant
Capacity: 627,000 m³/d
Located at south of Tel Aviv. 
Capital Cost: $500 million USD
Provides 20% of the Country water demand
 16" SWRO membranes in a vertical arrangement