This document summarizes a plant chemistry report on reverse osmosis systems. It covers topics like water properties, sea water impurities, the anatomy and principles of reverse osmosis systems. It also discusses common problems like boron removal, high pH scaling issues, membrane oxidation, and fouling causes like suspended solids, microbiological growth, and silica. Troubleshooting methods involving pressure vessel probing and single element performance tests are presented.

1. Plant Chemistry
Reveres Osmosis System
Prepared By : -
Umar Farooq
Senior Chemist / Shift Supervisor
MSC ( Chemistry ) MBA ( Marketing )
umar7325@yahoo.com
107301@se.com.sa
SEC Shoaiba Makkah
Saudi Arabia

2. Part
One
• Water Chemistry/Properties of Water
• Sea water impurities/ relative settling velocities of sand and silt.
• Definition & Simulation of Reveres Osmosis system
• Anatomy of Spiral Wound Element
• Principle of Reveres Osmosis/ Particle size and separation process
Part
Two
• What is Boron / Boron removing process
• Suspected problem during high pH operation
• Pressure vessel probing / Membrane Oxidation
• Ro System Normalization / Water analysis detail
• Causes of Mechanical leakage / Ro Element
Part
Three
• Membrane Fouling / Causes of Membrane fouling
• Topical fouling material /Suspended Solid, Coagulant
• Microbiological Fouling /Silica Fouling
• Membrane Degradation /Iron Fouling
• RO Troubleshooting Matrix /Factors which influence fouling
• Scaling / Causes of membrane scaling

3. Why Water is Unique
Water is only substance that exist in form of solid , liquid
and steam
Specific heat = 1calorie/gram
It expand = 1600 time
Three Isotopes = H2O , D2O , T2O
Heat of fusion = 144Btu / Lbs.
Heat of vaporization = 980 Btu / Lbs.
Freezing Expand = 1/9
Depending upon pressure ,its boil with in the temperature
= 35-704F*

4. Properties of Water
 It is chemical compound expressed by the formula
H2O.
 It is formed by two item of hydrogen and one atom of
oxygen
 Due to different electro negativities of hydrogen and
oxygen.H20 Molecule is electrically charged .
 When the other molecule combine with it then will be
formed hydrogen bonding
 Water is the best solvent . It dissolved different
substance In it and the process of dissolving
Is desolation
Model of hydrogen bonds
Between modules of water

5. Sea Water
 It is store house of impurities
 It contain 3.6% by weight of solids.
 Normally 75% impurities of sea water are Br, I , So4 , and Ca
,Mg , K , etc.
 Cat ion and Anion Salts in Sea water
Cations Anions
Calcium Ca++ Bicarbonate (HCO3
-),
Magnesium Mg+ + Carbonate (CO3
2-),
Sodium Na+ Sulfate SO4
2-
Iron Fe2+ (ferrous) Chloride Cl -
Aluminum AI3+ Nitrate NO3
-
Potassium K+ Fluoride F-

6. Relative velocities of sand and silt particles in
still water
Particle Diameter, mm Order of Magnitude Time Required to Settle 1 Foot
10.0 Gravel 0.3 Seconds
1.0 Coarse Sand 3 Seconds
0.1 Fine Sand 38 Seconds
0.01 Silt 33 Minutes
0.001 Bacteria 35 Hours
0.0001 Clay Particles 230 Days
0.00001 Colloidal Particles 63 Years

7. Simulation of Revers Osmosis System
Seawater supply
Pump D M F
Cartridge
filter
H P Pump
Booster
Pump
1st pass R O
E R D
2 ND pass R O
2 ND pass
Feed pump
Permeate
Transfer
pump
Potabilisation
Backwash
water Tank
Out fall
To SWCC
Shoaiba II
Storage Tank
S MBS
Anti sealant
Anti
Scalant
Caustic soda
Acid
Coagulant
Polym
er
Back
wash

8. What is Desalination
Reverse osmosis is a membrane process where salty source
water is supplied under
pressure to a semi-permeable membrane resulting in the
passage of fresh water through the membrane while the
membrane prevents the passage of the
dissolved minerals leaving them in the concentrated brine.
SWRO – means Seawater Reverse Osmosis unit also called
1st PASS RO.
BWRO – means Brackish Water Reverse Osmosis unit also
called 2nd Pass RO
ERD – means Energy Recovery Device.
PERMEATE – means the purified water passing through the
RO membranes. Also called product water.

9. Reverse Osmosis Membrane

10. The RO Membrane
 The membrane layer which makes the separation is extremely thin
(approximately 200 nanometer) (approximately 45 micron thick)
 It is supported on a porous polysulphone backing layer which gives the
membrane layer some strength
 The polysulphone is itself supported on a non-woven polyester backing fabric
(approximately 100 micron thick)
 Most RO membranes are made of cellulose acetate or polyamide composites
cast into a thin film as a sheet (or sometimes as fine hollow fibers)
 For potable water
 Applications the membrane type typically selected are thin film sheets made
from polysulphone with an ultra-thin (3 micron) polyamide salt rejecting layer

11. Anatomy of a spiral wound element
 The pressurized feed water flows in an axial direction through the feed
/brine spacer mesh.
 The pressure forces some of the feed water through the membrane layer,
leaving the majority of the dissolved salt on the feed side of the membrane
 The water crossing the membrane is called permeate.
 The permeate is collected in the permeate spacer material.
 The permeate spacer material is located between 2 sheets of membrane
 The 2 sheets of membrane plus the permeate spacer is collectively called
a leaf.

12. Spiral Wound Membrane Cutaway

13. Principle of Reveres Osmosis
The reverse osmosis process can be used to purify water by removing
dissolved minerals, and virtually 100% of colloidal and suspended matter to
produce high quality water of improved color, taste and other properties at
low cost compared to other purification processes.

14. Particle Size and Separation Process

15. Temperature Effect
Increasing Water Permeability Salt Rejection
Feed Temperature
Water permeability will increase about 3% per 1degC
 Highest water temperature must be considered for warranty exposure
 Highest operating pressure should be checked at lowest operating temperature.

16. Salinity Effect
Increasing Water Permeability Salt Rejection
Feed Salinity
Salt rejection decreases at lower feed salinity
(<400mg/l as NaCl) due to RO membrane negative charge effect.

17. pH Effect
Increasing Water Permeability Salt Rejection
Feed pH Almost same
•Salt rejection is rather constant over a broad pH range.
•Salt rejection will decrease at extremely high and low feed pH

18. What is Boron
Predominant reason for limiting Boron in water.
1)For Human
 Reproductive dander ( represent )
 Teratogenic properties ( suspected )
 WHO preliminary limit < 0.5mg/l
 EU guideline <1.0mg/l
2) Damage to Plant Crops
 Leaf damage ( Citrus tree is very sensitive)
 Reduce fruit yield
 Induce premature ripening
 Boron Concentration in sea water: 4.5-5.5mg/l
 Sea water distillation water by RO membrane does not meet requested Boron
revel.

19. Boron Removing Process

20. Boron Removing Process

21. Common Causes of RO System Problem
1) Suspected Problem during High pH operation.
Scaling problem is caused by excessive high pH operation ,
too low anti-Scalant dosing or too high recovery operation.
Scaling substance : CaCO3, Mg(OH)2
pH control, anti-Scalant dosing and correct recovery operation
are very important.
- Correct pH measurement,
- Good and enough pH meter calibration
- Correct anti-Scalant dosing
- Check anti-Scalant dosing rate and
consumption very frequently.
- 2nd pass brine pH & conductivity checking

22. Common Causes of RO System Problem
2) Membrane Oxidation
If composite polyamide RO membrane element are exposed to the oxidizing chemical
such as free chlorine ,chloramines, bromine, ozone, or other oxidizing chemicals,
irreparable damage is happened to the membrane ,normally evinced by decrees of
salt rejection.
Lead and element are typically more effected than the other in case of oxidizing
chemical present in RO feed water.
If several specific condition are assembled, chlorine generating problem might be
occurred.
Dissolved Oxygen.
NaHSO3 (SBS)
Heavy Metal ion
( Cu, Co, Mn, etc. Low concentration ,ppb order ,is enough)
High Salinity chlorine ion

23. Common Causes of RO System Problem
3) Chlorine Generation Mechanism under existing of Heavy Metal :
Even if RO feed water does not contain Chlorine, Chlorine will be generated
Following substances are required to generate chlorine.
1. Dissolved Oxygen, 2. NaHSO3 (SBS)
3. Chloride Ion 4. Heavy Metal Ion(Cu, Co, Mn. etc.)
Following chemical reactions in the process of generating chlorine (ex. with Copper).
SO3 2- + Cu 2+ SO3- + Cu + *1
SO 3 - + O2 SO 5- *1
SO 5- + SO3 2- SO5 2- + SO 3- *1
SO5 2- + Cl - ClO - +SO4 2- *1
(ClO - :Chlorine, Cl2 )
Reference
*1 : C. H. Barron and H. A. O’Hern, Chemical Eng. Sci.397-404

24. Common Causes of RO System Problem
4) High Permeate TDS
Poor permeate quality can be caused by the following:
 Changes in operating conditions
 Damage to membrane (oxidants, hydrolysis, etc..)
 Fouling
 Mechanical Leakage
5) Causes of Mechanical Leakage
 O-ring leak
 Interconnector or Permeate Tube crack
 Glue Line failure
 Membrane de lamination
 Membrane fracture
 Membrane mechanical abrasion
 Membrane degradation through chemical exposure

25. Membrane De lamination
Membrane
Delamination

26. Pressure Vessel Probing
A flexible tube is inserted through the permeate port of a
vessel to measure the permeate concentration at known
intervals through the vessel.
 Performed on vessels identified by the Pressure
Vessel Profile.
 Locates the elements or o- rings which are the source
of high salt passage

27. RO System Normalization

28. Calculation of Production
PERMEATE FLOW
% RECOVERY = ---------------------------------------- X 100
FEED FLOW
FEED TDS - PERMEATE TDS
% REJECTION = --------------------------------------- X 100
FEED TDS
PERMEATE TDS
% PASSAGE = --------------------------------------- X 100
FEED TDS

29. Water Analysis Details

30. Fouling
The deposition of suspended particles on the membrane
surface.
oFoul ant on the membrane surface increases the resistance to the flow of water through the membrane.
oFouling causes lower productivity at constant net pressure or
higher net pressure at constant productivity.
oSometimes higher salt passage will be caused by fouling.
Membrane fouling is caused by.
Improper pretreatment system
 pretreatment condition upset
Chemical dosing system upset
Improper material selection (piping, valve, pump, etc.)
 Improper flushing after shutdown
Scaling by excess recovery ratio
Biological contamination in feed water
Feed water chemistry change

31. Typical fouling materials
• Suspended Solid, Colloid, silt, clay
• Hydrates of metal oxides (Iron,
manganese, copper, aluminum,
etc.)
• Pretreatment coagulant
• Scale (Silica, calcium carbonate,
calcium sulfate, etc.)
• Organic chemicals (anti scalant,
cationic polymer, nonionic polymer,
etc.)
• Biological contamination and its
growth
Membrane Degradation

32. Membrane Fouling
Cause of Trouble : Fouling (Suspended Solid, Coagulant )
( SS leakage from pretreatment )
Fouling Amount : 62.4g
(Dry weight )
Ash Ratio : 75.9%
(SiO2:32%, Al:9.7%, Fe:4.8%)

33. Type's of Membrane Fouling
Silica Fouling
Microbiological
Fouling
Iron Fouling

34. RO Troubleshooting Matrix

35. RO Troubleshooting Matrix

36. Typical causes of DP increase
Upstream
Suspended solids, colloid, bacteria, silt, clay, iron corrosion and
pretreatment coagulant in the feed water
Downstream : scaling
Any stage mainly lead position : Biological fouling
Bio Fouling Control
 Prevent contact with direct sunlight wherever possible
 Disinfect make-up water
 Regularly maintain and disinfect filters
 Application of Biocides

37. Types of Scaling
• Scaling occurs
primarily in the
downstream
elements
because of he
higher
concentrations
existing in this
portion of the RO
system.
Mineral Scale
• Common Scaling
include
• calcium sulfate,
• calcium
carbonate.
• Silica
Calcium Sulphate
• Less common
Scaling include
• Calcium
Phosphate
• Calcium Fluoride
• Barium sulfate
Calcium Carbonate

38. Scaling caused by
Too much high recovery
High pH operation
Lower antiscalent dosing
Water chemistry change
Single element weight
checking
Single performance
checking
Single element
test on site

39. Single Element Performance Test on site
RO element outside visual checking
Single element weight checking
Single element performance checking
Measuring RO element weight after 30 min vertical standing
water drain.
New element weight : around 15 -16kg
(depend on water drain condition)
Weight checking will help to know fouling tendency in the pressure vessel.
RO element outside visual checking
Single RO element performance measuring equipment on site is very helpful
To check RO membrane performance more reliably.
To check RO membrane performance before / after cleaning.
To carry out pre-cleaning test (if single element cleaning test is available)