1.
REVERSE OSMOSIS SYESTEM
(University of Engineering and Technology, Lahore)

2.
Presenters
• Awais Yaqoob(2011-ch-32)
• Mujahad Ali(2011-ch-24)
1
• Engineer Haq Nawaz(2011-ch-44)
• Adeel Matloob(2011-ch-46)
2
• Rizwan Liaquat(2011-ch-72)
• Hafeez-ur-Rehman(2011-ch-80)
3

3.
Synopsis
Ion-Exchange Unit
Reactions Involved Merits and Demerits
Activated Carbon Bed
Factors Affecting its Performance Regeneration of Bed
Introduction to Reverse osmosis
Key Terms RO arrangements

4.
Advantages And Disadvantages of RO
Comparison b/w RO and other purification
techniques Conclusion
Basic Equations for RO Calculations
RO System Design Guidelines Steps to Design RO Membrane System
Cartridge Filter
Flow Meters Conductivity Meters

5.
Reverse Osmosis
• Reverse Osmosis is a technology used to remove majority of
contaminants from water by pushing water under high pressure
through a semi permeable membrane
• It is a process where you demineralize or deionize water

6.
Osmosis
• To understand purpose and process of RO, you must first
understand naturally occurring process of Osmosis
• It is a process where a weaker saline solution will tend to
migrate to a stronger saline solution
• For example, Plant root absorbs water from soil & Kidney
absorbs water from blood
• In diagram, salts are more concentrated in salty water so natural
flow of salts will be from right side to left side and water will
flow from right side to left side

7.
Reverse Osmosis
• RO is other way round of naturally occurring Osmosis
• Water is pushed through semi permeable membrane under high
pressure, thus leaving behind contaminants
• Pressure depends upon salt concentration of feed water.
• More the salts, more will be the applied pressure

8.
Cont.…
• Two types of water coming out of RO
– Permeate (containing less contaminants)
– Concentrate, reject or brine (containing more contaminants)
• Ro system employs cross filtration rather than standard
filtration where the Contaminants are collected within the filter
media.

9.
Salt Rejection %
• It tells you how effective the RO membranes are removing
contaminants.
• A well designed RO system with properly functioning RO
membranes will reject 95% to 99% of most feed water
contaminants
s𝑎𝑙𝑡 𝑅𝑒𝑗𝑒𝑐𝑡𝑖𝑜𝑛 %
=
𝐶𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝐹𝑒𝑒𝑑 − 𝐶𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒
𝐶𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝐹𝑒𝑒𝑑
• The higher the salt rejection, the better the system is
performing
• The lower the salt rejection meaning either filter needs to be
cleaned or replaced

10.
Salt Passage %
• It is the inverse of Salt rejection.
• It tells the amount of salt passing through RO system
Salt Passage % = (1-Salt rejection%)

11.
Recovery %
• It is the amount of water that is being
recovered as permeate
Recovery % =
𝑃𝑒𝑟𝑚𝑒𝑎𝑡𝑒 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 (𝑔𝑝𝑚)
𝐹𝑒𝑒𝑑 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 (𝑔𝑚𝑝)
* 100
• Industrial RO typically run anywhere from
50% to 85%

12.
Concentration Factor
• The concentration factor is related to RO system recovery
• The more water you collect as permeate, the more concentrated
salts you collect in concentrate stream which may lead to scaling
and fouling
Concentration Factor =
1
1−𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 %

13.
1 & 2 Stage RO System
• In 1 stage RO system, feed enters RO system as one stream
and leaves as concentrate and permeate.
• In 2 stage, concentrate from 1st becomes the feed water to the
2nd stage. Permeate water from 1st stage is collected and mixed
with permeate water from 2nd stage.

14.
1 stage RO

15.
2 Stage RO

16.
Single Pass RO & Double Pass RO
• In double pass RO, permeate from 1st pass becomes the feed to
2nd pass
• By going through 2 RO systems, a much higher quality
permeate can be achieved
• It also removes Carbon Dioxide by injecting Caustic Soda
between 1st and 2nd pass
• By adding Caustic Soda, we convert CO2 to carbonates and
bicarbonates which are removed in 2nd pass.

17.
Single Pass RO

18.
Double Pass RO

19.
Activated Carbon Bed
Presented By:
Mujahad Ali(2011-ch-24)

20.
Activated Carbon Bed
• Activated carbon is a form of carbon processed to have small,
low-volume pores that increase the surface area available
for adsorption.
• Due to its high degree of micro-porosity, just one gram of
activated carbon has a surface area in excess of 500 m2

21.
Activated Carbon Bed
• Active charcoal carbon filters are most effective at
removing chlorine, sediment, volatile organic
compounds (VOCs), taste and odor from water.
• They are not effective at removing minerals, salts, and
dissolved inorganic compounds.
• Typical particle sizes that can be removed by carbon filters
range from 0.5 to 50 micrometers.

22.
Factors Affecting the Operation
• Molecular weight
• pH
• Contaminant concentration
• Particle size
• Flow rate
• Temperature

23.
Molecular Weight
• As the molecular weight increases, the activated carbon
adsorbs more effectively because the molecules are less
soluble in water.
• The pore structure of the carbon must be large enough to allow
the molecules to migrate within.
• A mixture of high and low molecular weight molecules should
be designed for the removal of the more difficult species.

24.
pH
• Most organics are less soluble and more readily adsorbed at a
lower pH
• As the pH increases, removal decreases.
• Increase the size of the carbon bed by twenty percent for every
pH unit above neutral.

25.
Contaminant Concentration
• The higher the contaminant concentration, the greater the
removal capacity of activated carbon.
• The contaminant molecule is more likely to diffuse into a pore
and become adsorbed.
• Higher contaminant concentration may require more contact
time with the activated carbon.

26.
Particle Size
• Activated carbon bed is commonly available in 8 by 30 mesh
(largest), 12 by 40 mesh (most common), and 20 by 50 mesh
(finest).
• The finer mesh gives the best contact and better removal, but
at the expense of higher pressure drop.
• 8 by 30 mesh gives two to three times better removal than the
12 by 40, and 10 to 20 times better kinetic removal than the 8
by 30 mesh.

27.
Flow Rate
• The lower the flow rate, the more time the contaminant will
have to diffuse into a pore and be adsorbed.
• Adsorption by activated carbon is almost always improved by
a longer contact time.
• Whenever considering higher flow rates with finer mesh
carbons, watch for an increased pressure drop.

28.
Temperature
• Higher water temperatures decrease the solution viscosity and
increase diffusion rate.
• Higher temperatures can also disrupt the adsorptive bond.
• Generally, lower temperatures seem to favor adsorption.

29.
Regeneration of Bed
• The economics of the adsorption process greatly depend on the
reuse of activated carbon.
Various regeneration techniques are used such as;
• Thermal regeneration
• Chemical regeneration
• Wet air oxidation

30.
Presented By:
2011-ch-44
32
Water Softener

31.
33
• What is ion exchanger?
• Applications
• Formation of ion exchanger
• Hardness types and removal
• Resins types
• Regeneration
• Advantages & Disadvantages of ion exchanger
Water Softener/Ion Exchanger

32.
34
Ion exchange is an adsorption phenomenon where the mechanism
of adsorption is electrostatic.
What is ION Exchange?

33.
35
• Ca , Mg (hardness removal) exchange with Na or H.
• Fe, Mn removal from groundwater.
• Demineralization (exchange all Cations for H all anions for
OH)
Applications

34.
36
Resins are formed by polymerization process .
• Typical procedures involve heating aqueous solutions
of alumina and silica with sodium hydroxide.
• Equivalent reagents include sodium aluminate and sodium
silicate.
Formation of Resins

35.
37
1) Temporary hardness
2) Permanent hardness
Hardness

36.
Removal of Temporary Hardness
38
(1)Boiling Method:
Ca ( HCo3)2 ---> CaCo3 + Co2 + H2o
Mg ( HCo3)2 ---> MgCo3 + Co2 + H2o
(2)Clark’s Method:
Ca (HCo3)2+ (Ca(OH)2 ---> 2CaCo3+ 2 H2o

37.
Removal of Permanent Hardness
39
(1)Reaction with Washing Soda
Na2Co3 + Caso4 ---> CaCo3 + Na2so4
(2) Ion Exchange Method:
Caso4 + Na2 – zeolite ---> Ca - zeolite + Na2so4

38.
Resin Classification
40
 Cationic resin
 Anionic resin

39.
Cationic Resin Vs. Anionic Resins
41
• Those that exchange positive ions, called cation exchange
resins.e.g Ca+2, Mg+2
• Those that exchange negative ions, called anion exchange
resins.e.g Cl-1, SO4-2,

40.
42
Regeneration and its Types
Counter-current
Regeneration
Co-current Regeneration

41.
Co-current Regeneration
43

42.
Counter-current Regeneration
44

43.
Regeneration Reaction
45
Ca- zeolite + NaCl ---> Na2 – zeolite + CaCl2

44.
Advantages of Soft Water
46
• Longer appliance life for washing machines
• Less use of household cleaning products, such as detergents.
• Your clothes last longer and remain brighter longer if they are
washed in soft water.
• Your plumbing will last longer. Hard water can cause a build
up of scale from mineral deposits
• Your skin is softer when you bathe with soft water

45.
Advantages of Ion Exchange Column
47
• It is compact and has a low capital cost
• The chemicals used are safer for the operator to handle and
operation
• It can be almost totally automated
• It can be used for production of good quality water

46.
Disadvantages
48
• Adsorption of Organic Matter
• Iron Fouling
• Bacterial Contamination

47.
Cartridge Filter

48.
Cartridge Filter
• Fabric or Polymer-Based
• To remove Particulate material
• Designed along a central core
• Pleats/ Foldings

49.
Top Cap
Bottom
Cap
Pleated
Media

50.
Working of
Cartridge
Filter
• Pressurized Fluid
• Passage through
the Pore
• Suspended Solid
material
• Clogging
• Pressure drop

51.
Application
• Filtration of surface water or ground water
under the influence of surface water.
• Prefiltration prior to subsequent treatment.
• Solids removal.

52.
Rotameter

53.
Rotameter
• Variable area meters
• Cross Sectional area
• Floating

54.
Working of
Rotameter
• Volumetric
Flow rate
increases drag
force
• Cone shaped
area decreases
the buoyancy
force
• Equilibrium
with the float

55.
Why to use Cartridge Filter
and Rotameter

56.
Cartridge Filters
Cartridge Filters are less expensive then the other sediment filters
Minimum maintenance is involved
Can filter out anything about 5 to 10 micrometre in size
Can be both the surface and depth type filters
Ease in cleaning

57.
Rota Meter
Relatively Simple Device to manufacture
Requires no External power or fuel to run
Scale of rotameter is almost linear
Clear glass is used which is highly resistant to shock

58.
RO System

59.
REVERSE OSMOSIS SYSTEM DESIGN
Presented By:
Rizwan Liaquat(2011-ch-72)

60.
Basic Equations for RO Calculations
Water Transport
Solute Transport
Correlation of Operating Conditions

61.
Water Transport
• Water transport through the membrane is expressed as a
permeate flux.
• The permeate flux is proportional to the net driving pressure
(NDP).
Where

62.
CONTD…
• The product flow rate can be obtained by multiplying the
permeate flux by total membrane area.
• The pressure drop is calculated by the average flow rate
(feed and concentrate) as follows:
In which a and b are coefficients, specific for element and
feed spacer configuration. The values for these coefficients are
obtained experimentally.

63.
Solute Transport
• Solute transport through an RO membrane is expressed as a
solute flux.
• This solute flux is proportional to the concentration difference
across the membrane.
• The average feed concentration (feed and concentrate) is
used in the feed side to calculate solute transport.
• And the rate of solute transport is defined by rejection or salt
passage as follows:
In which: B, solute permeability, R, rejection, SP, salt passage

64.
Correlation of Operating Conditions
• RO membrane system performance (flux and rejection or salt
passage) is influenced by operating conditions such as operating
pressure, temperature, feed concentration etc.
• AS = Specific flux at operating conditions,
• An= Specific flux at nominal conditions
• SPS= Salt passage at operating conditions,
• SPn= Salt passage at nominal conditions
• (JV) S= Permeate flux at operating conditions, (JV) n,= Permeate flux
at nominal conditions
• TCF = Correlation factor of temperature (1; on specific flux, 2; on salt
passage)
• SCF= Correlation factor of feed concentration (1; on specific flux, 2;
on salt passage)
• FF= Fouling factor

65.
RO System Design Guidelines
Fouling Tendency with Operating Conditions
Recommended Range of Element Operating Conditions (Design
Guideline)

66.
Fouling Tendency with Operating Conditions
• Membrane fouling is caused by particles and colloidal
materials which are present in the feed water and become
concentrated at the membrane surface.
• The Silt Density Index (SDI) of pretreated feed water is an
index of the fouling potential of particle or colloidal materials
in the RO system.
• The concentration of the fouling materials at the membrane
surface increases with increasing permeate flux, increasing
element recovery and decreasing concentrate flow rate.
• Therefore the average permeate flux of the RO system
should be low if a strong fouling environment is
anticipated.

67.
Recommended Range of Element Operating
Conditions
The maximum lead element permeate flux
The maximum average permeate flux
The maximum recovery (system and element)
The maximum feed flow rate
The minimum concentrate flow rate

68.
Steps to Design RO Membrane System
System Design Information and Feed Water
Selection of Element Type and Average Permeate Flux
Calculation of Number of Total RO Elements
Decision of Recovery Rate
Decision of Number of Stages
Decision of Number of RO Elements per Pressure Vessel
Decision of Element Arrangement
Relations between Nominal Performances and Field Results

69.
System Design Information and Feed Water
Water source and pretreatment required
Customer/process required product flow rate
Application of water being treated
Expected recovery rate
Annual water temperature
Required product water quality, operating
pressure limit, etc.

70.
CONTD…
• The RO membrane system highly depends on the available
feed water.
• Therefor, the System design information should be
thoroughly studied and considered in selection of the RO
system design.
• If the required permeate water quality is so high that the
quality cannot be achieved by 1pass RO system, and then
a 2 pass RO system should be considered.
• As an alternative to the 2 pass RO, an ion exchange resin
system may also be a viable design option

71.
Selection of Element Type and Average
Permeate Flux
• According to the feed water source, pretreatment and feed
water salinity, the type of RO membrane element is
selected.
• Once the water source, pretreatment and RO element type
are fixed by the designer, the recommended value of the
average permeate flux (also called “design flux”) is
determined by pilot experiment data or customer’s
experience.

72.
Calculation of Number of Total RO Elements
• The relationship between the number of total elements, the
product flow rate and the average permeate flux is expressed
as follow equation:
• In Which:
• NE= Total element numbers
• Qp= Product flow rate
• JV,ave= Average permeate flux
• (MA)E= Membrane area of element

73.
Decision of Recovery Rate
• In an RO membrane system, a recovery rate as high as
possible is desirable
• A high recovery rate can also cause some problems as
follows:
 Possibility of scale formation increase because of the increase
of concentration factor
 Osmotic pressure increase because of the increase of
concentration factor
 Concentrate flow rate decrease
 Permeate water quality deterioration because of average feed
concentration increase

74.
CONTD…
• Generally recovery rate is decided by scale formation and
by feed pressure limit.

75.
Decision of Number of Stages
• The number of RO stages defines how many pressure
vessels are in series in the RO membrane system.
• Every stage consists of a certain number of pressure vessels in
parallel.
• The number of stages is a function of the system recovery
rate, the number of elements per vessel, and the feed water
quality

76.
CONTD…

77.
Decision of Number of RO Elements per
Pressure Vessel
• RO membrane elements can be coupled together in series
in the pressure vessel, typically 1-8 elements per one
pressure vessel.
• In deciding the number of RO elements per pressure
vessel, plant size is usually considered first.
• In a large-scale plant (> 40 m3/h), 6-8 elements per pressure
vessel are usually adopted, and in a smaller plant, 3-5
elements per pressure vessel.
• In all cases, the space required to install or remove the RO
elements should be considered in the plant design.

78.
CONTD…
• By increasing the number of RO elements per pressure
vessel, almost all RO design parameters will change.

79.
Decision of Element Arrangement
• For the decision of element arrangement, the system
design parameters should be consistent with the design
flux guideline.
• To decide the array, several calculations for case study
should be done by computer program and these results
should be compared.

80.
Relations between Nominal Performances and
Field Results
• A higher nominal flow rate element will require lower
feed pressure.
• At different test conditions and /or different membrane
area, feed pressure will be defined by water permeability.
• A higher salt rejection element will produce a permeate
of lower salinity.
• A lower relative salt passage element (multiplier of
nominal permeate flux by nominal salt passage) will
produce a permeate of lower salinity.

81.
Advantages And Disadvantages of RO
Advantages:
1. Low Energy Requirements.
RO performs a separation without a phase change. Thus, the energy
requirements are low
2. Less Space requirements.
RO systems are compact, and space requirements are less than with other
desalting systems, e.g. distillation
3. Easy to Understand
RO equipment is standardized - pumps, motors, valves, flowmeters, pressure
gages, etc. Thus, the learning curve for unskilled labor is short.

82.
4. Little labor required:-
Many RO systems are fully automated and designed to start-up and shutdown
automatically through interlocks. Thus, RO plants usually require little labor.
5. Easy maintenance:-
Due to their modular design, maintenance is easy. maintenance can be
performed without shutting down the plant.
Also the expansion of plant is an easy option.
6. Remove unpleasant smell:-
RO removes dissolved minerals and other contaminants that cause to smell
unpleasant.

83.
7. Efficient for plumbing system:-
Removal of dissolved minerals, metals and other particles benefits plumbing
systems, Nothing in the water to corrode pipes.
8. Removes bacteria and pathogens in drinking water
Biological contaminants present in tap water are harmful bacteria that can
cause diseases. And if you happen to drink the water, you may acquire fatigue,
diarrhea, excessive gas, bloating, loss of interest in food and weight loss.
9. Better taste and smell
In this process, 98% of chemicals are removed from your drinking water so it
will not taste of chlorine anymore.

84.
10. Reduces the risk of having diseases and illnesses
Chlorine, asbestos, mercury and lead are some of the toxins that can be
found in tap water. Reverse osmosis offers defense between the body
and the other 2100 known toxins.
11. Children- friendly
Drinking pure water is very important to children’s developing immune
systems. Water filters such as reverse osmosis systems provide the healthiest
water for them.

85.
Disadvantages
1. Purification Limits
Many RO systems come with carbon pre-filters. That’s because
chlorine and Volatile Organic Chemicals (VOC’s) are smaller than
water molecules so they can’t be filtered on the reverse osmosis
membrane.
2. Speed and Efficiency
These systems can only produce 15 (gpd). It works against
standard osmotic pressure so the reverse osmosis process is fairly
slow. And requires 3 to 10 gallons of untreated water to make a
single gallon of purified water, which is wasteful and expensive.

86.
3. Maintenance:-
The maintenance of RO system must be done regularly. its filters must be
cleaned to avoid the fouling of the membranes. The pre-filters must be
changed annually, while the RO membrane should be replaced every 2-3 years.
4. Pressure limitations:-
The applied pressure must exceed the osmotic pressure to separate the solute
from the solvent.
The max pressure for seawater devices is 800 - 1000 psig,
For brackish water varies from 400 - 600 psig.
Due to the high pressure requirement RO is usually not applicable for
concentrated solutions.

87.
5. Pretreatment Required:-
Because all RO membranes and devices are susceptible to
fouling, the RO process usually cannot be applied without
pretreatment.
6. Compatibility of feed Stream:-
RO feed streams must be compatible with the membrane and
other materials of construction used in the devices.

88.
7. High Temperature
Usually at high temperature the RO process is favorable but the
problem at high temperature is the increase in pore size of the
membrane so it requires optimum conditions for temperature.
8. High Conductivity
As Conductivity is directly proportional to total dissolved solids
so It means high conductivity liquids require more treatment and
hence more time required for the RO purification system.

89.
• Comparison b/w RO and other purification techniques
The given below are some techniques comparable with Reverse
Osmosis
1. Ion Exchange
2. Distillation
3. Activated Carbon
4. Precipitation
5. Ultraviolet Radiation
6. Boiling

90.
Disease
Element Causing
Disease
Reverse Osmosis
RO
Ion Exchange Distillation
Activated
Carbon
Precipitation
Ultra-
Violet
Boiling
Cancer Initiation Chlorine # x B # x x X
pH In-equilibrium Alkali Fume # A # x x x X
Cancer Initiation Chloroform # x B # x x X
Bacteria Infections
Disease
Bacteria # x # B x # #
Virus Infections Disease Viruses # x # x x # #
Intoxication, Liver
Disease
Agricultural Chemicals # x # # x x X
Hepatitis Dioxin # x # B x x X

91.
Cancer Radioactive Material A A B x x x X
Anorexia Taste and Odor # x x # x x X
Calculus, Enteritis Precipitate # x # B # x X
Poisoning Organic Substances # x B # X x X
Cancer Initiation Fluoride A A # x x x X
Cancer Initiation Fluorescence # x x x x x X
Neuritis Arsenic A A A x x x X
Calculus Calcium A A A x x x X

92.
Notalgia Cadmium A A A x x x X
Nephrosis, Leading
Poisoning
Lead A A # X x x X
Organic Phosphorus
Poisoning
Phosphorus A A # X x x X
Electrolyte In-equilibrium Potassium A A A X x x X
Hypersensitive Heart
Disease
Sodium A A # X x x X
Digestive System Disease Sulphur A A A X x x X
Digestive System Disease Magnesium A A # # x x X
Where #=98-99% Removal ; A =96-99% Removal; B =Partial Removal; x =Can not Remove