See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/283734409

REPORT On Reverse Osmosis Desalination

Research · November 2015

DOI: 10.13140/RG.2.1.4855.7521

CITATIONS READS

0 2,712

1 author:

Ansa Aman Ullah

COMSATS Institute of Information Technology, Lahore,Pakistan
1 PUBLICATION   0 CITATIONS   

SEE PROFILE

All content following this page was uploaded by Ansa Aman Ullah on 13 November 2015.

The user has requested enhancement of the downloaded file.

 12/26/2014
CHEMICAL ENGINEERING DEPARTMENT

REPORT ON REVESRE OSMOSIS

COURSE: MASS TRANSFER OPERATIONS LAB

SUPERVISOR: ENGR. MUHAMMAD ABDUL QYYUM

SUBMITTED BY:

ANSA AMAN ULLAH CHE-SP12-010(B)

SIDRA YASIN CHE-SP12-084(B)

MUHAMMAD USMAN JAVED CHE-SP12-060(B)

COMSATS INSTITUTE OF INFORMATION AND TECHNOLOGY,

LAHORE CAMPUS
 2

CONTENTS
1. MASS TRANSFER OPERATION ................................................................... 4
1.1 CLASSIFICATION .............................................................................................................. 4
1.2 SIMILARITIES BETWEEN VARIOUS MASS TRANSFER OPERATIONS .................... 4
1.3 COMPARARISON OF VARIOUS MASS TRANSFER TECHNIQUES ............................ 5
1.4 COMPARISON OF REVERSE OSMOSIS WITH OTHER MASS TRANSFER
TECHNIQUES .................................................................................................................................. 6

2 WATER ............................................................................................................... 9
2.1 CHEMICAL COMPOSITION: ............................................................................................ 9
2.2 CHEMICAL NATURE: ....................................................................................................... 9
2.3 WATER SOURCES AND CONTAMINANTS: .................................................................. 9
2.4 POTABLE WATER ........................................................................................................... 12
2.5 BOILER-FEED-WATER-[27] ........................................................................................... 12
2.5.1 BFW Contaminants , Their Effect and Possible Treatment : .......................................... 13

3 WATER TREATMENT .................................................................................. 16

3.1 PRETREATMENT[29] ...................................................................................................... 16
3.1.1 PRETREATMENT OF WATER PRIOR TO RO-TREATMENT[30] .......................... 16
3.2 TREATMENT TECHNIQUES[30] .................................................................................... 17

4 RO-MASS TRANSFER TECHNIQUE .......................................................... 20

5 WHEN WILL BE THE RO IS PREFERRED OVER OTHER
SEPARATION TECHNIQUES [31]: .................................................................... 22
6 OSMOSIS .......................................................................................................... 22
7 REVERSE OSMOSIS ...................................................................................... 23
7.1 OBJECTIVES ..................................................................................................................... 24
7.2 BLOCK SCHEMATIC DIAGRAM FOR RO-OPERATION............................................. 24
7.3 FLOW MECHANISMS THROUGH RO-MEMBRANES ................................................. 25
7.3.1 CROSS-FLOW FILTRATION ...................................................................................... 25
7.3.2 DEAD-END FILTRATION ........................................................................................... 26
7.4 BASIC DEFINITIONS AND TERMS................................................................................ 27
7.4.1 RECOVERY................................................................................................................... 27
7.4.2 REJECTION ................................................................................................................... 28
7.4.3 SALT PASSAGE ........................................................................................................... 29
7.4.4 FLUX.............................................................................................................................. 29
7.4.5 CONCENTRATION POLARIZATION ........................................................................ 29
7.4.6 BETA.............................................................................................................................. 30
7.4.7 FOULING....................................................................................................................... 31
7.4.8 SCALING ....................................................................................................................... 31
7.5 DESIGN CONSIDERATIONS/FACTORS FFECTING RO ............................................. 32
7.5.1 TOTAL DISSOLVED SOLIDS ..................................................................................... 32
7.5.2 TEMPERATURE ........................................................................................................... 33
7.5.3 PRESSURE .................................................................................................................... 34
7.5.4 FEED WATER FLOW ................................................................................................... 34
7.5.5 CONCENTRATE FLOW ............................................................................................... 34
 3

7.5.6 BETA.............................................................................................................................. 35
7.5.7 RECOVERY................................................................................................................... 35
7.5.8 FLUX.............................................................................................................................. 36

8 MEMBRANE[35] ............................................................................................. 36
8.1 MODULES[37] .................................................................................................................. 37
8.1.1 TUBULAR MODULES : ............................................................................................... 37
8.1.2 FLAT SHEET MODULES : .......................................................................................... 38
8.1.2.1 SPIRAL WOUND MODULE .................................................................................... 38
8.1.3 COMPARISON OF CHARACTERISTICS OF VARIOUS MODULES [35] ............. 39
8.2 GENERALLY USED MEMBRANES ............................................................................... 39
8.2.1 Cellulose Acetate Membranes[37].................................................................................. 39
8.2.2 Thin Film Composite Membranes[37] ........................................................................... 40
8.3 FOULING FACTORS AND METHODS TO AVOID : ..................................................... 41

9 APPLICATIONS [34]: ..................................................................................... 42

10 EXPERIMENTAL ANALYSIS [39]............................................................... 42
10.1 PROCEDURE: ................................................................................................................... 42
10.2 OBSERVATIONS AND CALCULATIONS: .................................................................... 42
10.2.1 OBJECTIVE 1 :.......................................................................................................... 42
10.2.2 OBJECTIVE 2:........................................................................................................... 43
10.2.3 OBJECTIVE 3: To Check The Performance Of RO-apparatus ................................. 43
10.2.4 OBJECTIVE 4: TO Study And Compare The RO Feed Water, Permeate And
Retentate 43
10.2.5 OBJECTIVE 5:To study the effect of pressure on RO performance by qualitative
analysis of permeate and retentate. ............................................................................................ 43
10.3 RESULTS AND DISCUSSIONS: ...................................................................................... 44
10.3.1 Comparison Of Properties Of Various Types Of Water ............................................. 44
10.3.2 RO Water Analysis ..................................................................................................... 45
RO WATER ANALYSIS ........................................................................................................... 45

11 REFERENCES: ................................................................................................ 46
 4

REPORT ON REVERSE OSMOSIS TECHNIQUE

1. MASS TRANSFER OPERATION [1]
Mass transfer operation is the one in which the following phenomena must exist:
1. Two or more phases must come in contact with each other.
2. Materials should flow from one phase to other.
3. A part of the total flow must be by molecular motion or molecular diffusion.

1.1 CLASSIFICATION
The mass transfer operations have been classified according to the phase contact
in table below:

1.2 SIMILARITIES BETWEEN VARIOUS MASS TRANSFER

OPERATIONS
There are many similarities between the various mass transfer operations. They are:
1. Phase equilibrium is reached after a sufficiently long period of contact.
2. Rate of transfer is calculated by deviation from equilibrium concentration.
3. Equilibrium exists at phase interphase or there is no resistance to mass
transfer at the interface, with some exceptions.
4. Material transfer is due to combined effect of molecular diffusion and
turbulence.
 5

1.3 COMPARARISON OF VARIOUS MASS TRANSFER

TECHNIQUES

Distillation [2] Evaporation[2]

Mixture of components are separated on Separate single component (usually
the basis of their different volatility water) from nonvolatile component
Vapors consist of at least two Vapors consist of one component
components

Distillation [2] Absorption[2]

Vapor is produced in each stage by Feed is a mixture of gases
partial vaporization
Diffusion is both from liquid to gas and Diffusion is unidirectional
gas to liquid
Ratio of Liquid to gas flow rate is low Ratio of Liquid to gas flow rate is high

Absorption Adsorption
Bulk phenomena Surface phenomena
Molecule dissolve in bulk of fluid[3] Molecule binds on surface of solid[3]
Concentration of adsorbed material is Concentration of absorbed material is
high on surface[4] uniform throughout the bulk[4]

Evaporation Drying
It is used when large amount of It is used when small amount of
water/liquid is present in water[6] water/liquid is present in water[6]
To obtain saturated solution or recovery Final product is free flowing powder of
of valuable product[6] individual particles, agglomerates and
granules[5]
Vapor is of single component[7] Vapors may of multicomponent

Liquid Liquid Extraction [8] Leaching[8]

Liquid extraction Solid extraction
LLE is used to separate two miscible Is used to dissolve soluble matter from
liquids by the use of solvent which its mixture with an insoluble solid
prefer to dissolve one of them
 6

Distillation [9] Extraction[9]

Constituent of liquid mixtures are Constituent of liquid mixtures are
separate by using thermal energy separate by using insoluble solvent

Constituent of liquid mixtures are Constituent of liquid mixtures are

separate due to difference in their separate due to difference in their
boiling point solubility
It give almost pure product It does not give product. further
treatment is necessary
Require thermal energy Require mechanical energy for mixing
and separation

1.4 COMPARISON OF REVERSE OSMOSIS WITH OTHER

MASS TRANSFER TECHNIQUES

Reverse Osmosis Ion Exchange

Continuous process[10] Batch process[10]
More Sensitive to incoming suspended particles Less Sensitive to incoming suspended
Pretreatment is required[10] particles(1)
Sensitive for temperature variation Less Sensitive for temperature
Salt passage is increased with increase in variation[10]
temperature[10]
RO removes compound on basis of their sizes It removes ions and doesn’t remove
Small ions or molecule (Na,Cl,CO2) are partially nonionic [10]
removed[10]
RO is partially demineralized process[10] Complete demineralized process[10]
High energy efficient Regeneration of chemical is main running
Electrical energy is used for pumping [11] cost[11]

Reverse Osmosis Electrodialysis

Driving force is pressure [12] Driven force is electrical energy [12]
Sensitive for temperature variation (15 C to 25 C) Operation at elevated temperature up to 50
Salt passage is increased with increase in C [12]
temperature [12]
Can remove neutral toxic components such as It cannot remove toxic components such as
bacteria and viruses [12] bacteria and viruses and may require post
treatment[13]

more sensitive to membrane fouling Less sensitive to membrane fouling

pretreatment is required[13] Less raw water pretreatment[11]
No generation of chlorine gas[13] Generation of chlorine gas at anode cause
corrosion problem in surrounding of
plant[13]
Energy loss in RO is caused by friction Energy loss is caused by friction of ions on
experienced by water molecule on their pathway their pathway through membrane from
through membrane matrix [12] dilute to brine solution [12]
 7

Energy loss is independent of feed salt Both the energy consumption and required
concentration [12] membrane area is increased with increase
of salt concentration [12]

[10]

Reverse Osmosis Distillation

Low energy consumption[15] High energy consumption[15]
Output is higher than distillation Low yield[14]
It does not remove dissolved gases in It remove dissolve gases in water(CO2 AND
water(CO2 AND O2) [10] O2)[14]
Require less time for desalination[15] Require more time than RO for
desalination[15]

Reverse Osmosis Evaporation

Is also use to obtain concentrated liquid To obtain saturated solution or valuable
food/beverages[16] product
It is used to concentrate heat sensitive By evaporation heat sensitive material can
liquid(reduce heat damage to food color and damage[16]
taste[16]
Energy efficient Use thermal energy to vaporize liquid[16]
As only pressure energy is used[16]
It particularly use full to obtain pre-concentrator
Before evaporation [16]
Not suitable for viscous fluids[16] Used for evaporation of slurries
It is useful to concentrate the solution up to the Evaporation is used to concentrate the solute
point where osmotic pressure become up to its dryness[17]
excessive[17]
 8

[18]

Reverse Osmosis Ultrafiltration

Both have same working principle[19]
The main difference is between them the size of particle that can pass through
membrane[19]
Allow smallest particle to flow Limits the flow of macromolecule
Water molecule, some salts and volatile (proteins, starch and gums)
component[19] [19]
Osmotic pressure is greater for small solute Osmotic pressure is low for
molecule[20] macromolecule
[20]
Operating pressure is high than Operating pressure is lower than reverse
ultrafiltration[20] osmosis[20]

[21]
 9

2 WATER
2.1 CHEMICAL COMPOSITION:
Water molecule consist of one oxygen atom covalently bonded to two hydrogen
atoms. It has the following structure:

Fig. water molecule with hydrogen bonding [22].

2.2 CHEMICAL NATURE:

Water is a polar molecule, and although electrically neutral it has a polar nature
such that the molecule has a region of negative charge near the O atoms and positive
charge near the H atom. This dipolar nature gives water important properties such as
its ability to act as a solvent. The polar nature of water leads to H bonding of water
molecules and other molecules. Hence due to this chemical nature, many substances
(solutes) dissolved in water to varying degrees, depending on specific chemical
properties, are found.

2.3 WATER SOURCES AND CONTAMINANTS:

The sources of water that are potentially useful to humans fall into four categories,
namely, oceans, lakes, surfaces, and sub surfaces. [23]

Water, being a universal solvent, normally contains many impurities that it picks up
from its surroundings. The common impurities found in fresh water are: [24]

Means of
Constituent Chemical Formula Difficulties Caused
Treatment
imparts unsightly
appearance to water;
coagulation,
non-expressed in deposits in water lines,
Turbidity settling, and
analysis as units process equipment, etc.;
filtration
interferes with most
process uses
chief source of scale in softening;
calcium and magnesium heat exchange equipment, demineralization;
Hardness salts, expressed as boilers, pipe lines, etc.; internal boiler
CaCO3 forms curds with soap, water treatment;
interferes with dyeing, surface active
 10

etc. agents

foam and carryover of

lime and lime-soda
solids with steam;
bicarbonate(HCO3 ), embrittlement of boiler softening; acid
-

carbonate (CO32-), and steel; bicarbonate and treatment; hydrogen

Alkalinity -
hydroxide(OH ), zeolite softening;
carbonate produce CO2 in
expressed as CaCO3 demineralization
steam, a source of
dealkalization by
corrosion in condensate
anion exchange
lines
Free
H2SO4 , HCI. etc., neutralization with
Mineral corrosion
expressed as CaCO3 alkalies
Acid
aeration,
corrosion in water lines,
Carbon deaeration,
CO2 particularly steam and
Dioxide neutralization with
condensate lines
alkalies
hydrogen ion
concentration defined pH varies according to
as: acidic or alkaline solids pH can be increased
PH 1 in water; most natural by alkalies and
waters have a pH of 6.0- decreased by acids
pH = log
8.0
[H+]
adds to solids content of
water, but in itself is not demineralization,
usually significant, reverse osmosis,
Sulfate SO42-
combines with calcium to electrodialysis,
form calcium sulfate evaporation
scale
demineralization,
adds to solids content and
reverse osmosis,
Chloride Cl - increases corrosive
electrodialysis,
character of water
evaporation
adds to solids content, but
is not usually significant
industrially: high demineralization,
concentrations cause reverse osmosis,
Nitrate NO3-
methemoglobinemia in electrodialysis,
infants; useful for control evaporation
of boiler metal
embrittlement
adsorption with
cause of mottled enamel
magnesium
in teeth; also used for
hydroxide, calcium
Fluoride F- control of dental decay:
phosphate, or bone
not usually significant
black; alum
industrially
coagulation
 11

adds to solids content of

demineralization,
water: when combined
reverse osmosis,
Sodium Na+ with OH-, causes
electrodialysis,
corrosion in boilers under
evaporation
certain conditions
hot and warm
process removal by
magnesium salts;
scale in boilers and
adsorption by
cooling water systems;
highly basic anion
Silica SiO2 insoluble turbine blade
exchange resins, in
deposits due to silica
conjunction with
vaporization
demineralization,
reverse osmosis,
evaporation
aeration;
Discolors water on coagulation and
precipitation; source of filtration; lime
Fe2+ (ferrous) deposits in water lines, softening; cation
Iron
Fe3+ (ferric) boilers. etc.; interferes exchange; contact
with dyeing, tanning, filtration; surface
papermaking, etc. active agents for
iron retention
Manganese Mn2+ same as iron same as iron
usually present as a result
of floc carryover from
clarifier; can cause improved clarifier
Aluminum AI3+
deposits in cooling and filter operation
systems and contribute to
complex boiler scales
corrosion of water lines, deaeration; sodium
Oxygen O2 heat exchange equipment, sulfite; corrosion
boilers, return lines, etc. inhibitors
aeration;
Hydrogen cause of "rotten egg" chlorination; highly
H2S
Sulfide odor; corrosion basic anion
exchange
cation exchange
corrosion of copper and with hydrogen
Ammonia NH3 zinc alloys by formation zeolite;
of complex soluble ion chlorination;
deaeration
refers to total amount of lime softening and
dissolved matter, cation exchange by
Dissolved determined by hydrogen zeolite;
none
Solids evaporation; high demineralization,
concentrations are reverse osmosis,
objectionable because of electrodialysis,
 12

process interference and evaporation

as a cause of foaming in
boilers
refers to the measure of
undissolved matter, subsidence;
determined filtration, usually
Suspended
none gravimetrically; deposits preceded by
Solids
in heat exchange coagulation and
equipment, boilers, water settling
lines, etc.
refers to the sum of
see "Dissolved
dissolved and suspended
Total Solids none Solids" and
solids, determined
"Suspended Solids"
gravimetrically

2.4 POTABLE WATER

 Potable water is water that has been either treated, cleaned or filtered and
meets established drinking water standards or is assumed to be reasonably
free of harmful bacteria and contaminants, and considered safe to drink or
use in cooking and baking.[25]
 Potable water is fresh water that is sanitized with oxidizing biocides such as
chlorine or ozone to kill bacteria and make it safe for drinking purposes.[26]
 By definition, certain mineral constituents are also restricted. For example,
the chlorinity will be not more than 250 ppm chloride ion in the United
States or 400 ppm on an international basis.
 Examples of potable water would be that from treated municipal water
systems, water that has been UV filtered or purified by reverse osmosis.[25]

2.5 BOILER-FEED-WATER-[27]

Feed-water composition depends on the quality of the make-up water and the
amount of condensate returned to the boiler.

The principal difficulties caused by water in boiler are:

 Scaling
 Foaming and priming
 Corrosion
Proper treatment of boiler feed water is an important part of operating and
maintaining a boiler system. As steam is produced, dissolved solids become
concentrated and form deposits inside the boiler. This leads to poor heat
 13

transfer and reduces the efficiency of the boiler. Dissolved gasses such as
oxygen and carbon dioxide will react with the metals in the boiler system
and lead to boiler corrosion. In order to protect the boiler from these
contaminants, they should be controlled or removed, through external or
internal treatment.

2.5.1 BFW Contaminants, Their Effect and Possible Treatment:

Following table constitutes the list of the common boiler feed water contaminants, their effect
and their possible treatment.

IMPURITY RESULTING IN GOT RID OF BY COMMENTS

Soluble Gasses
Water smells like
Found mainly in
Hydrogen Sulphide rotten eggs: Tastes Aeration, Filtration,
groundwater, and
(H2S) bad, and is corrosive and Chlorination.
polluted streams.
to most metals.
Filming, neutralizing
Corrosive, forms Deaeration,
amines used to
Carbon Dioxide (CO2) carbonic acid in neutralization with
prevent condensate
condensate. alkalis.
line corrosion.
Deaeration & Pitting of boiler
Corrosion and chemical treatment tubes, and turbine
Oxygen (O2) pitting of boiler with (Sodium blades, failure of
tubes. Sulphite or steam lines, and
Hydrazine) fittings etc.
Suspended Solids
Tolerance of approx.
Sludge and scale Clarification and 5ppm max. For most
Sediment & Turbidity
carryover. filtration. applications, 10ppm
for potable water.
Found mostly in
surface waters,
caused by rotting
vegetation, and farm
run offs. Organics
Carryover, foaming, break down to form
Clarification; organic acids.
deposits can clog
Organic Matter filtration, and
piping, and cause Results in low of
chemical treatment
corrosion. boiler feed-water
pH, which then
attacks boiler tubes.
Includes diatoms,
molds, bacterial
slimes,
 14

iron/manganese
bacteria. Suspended
particles collect on
the surface of the
water in the boiler
and render difficult
the liberation of
steam bubbles rising
to that surface.
Foaming can also be
attributed to waters
containing
carbonates in
solution in which a
light flocculants
precipitate will be
formed on the
surface of the water.
It is usually traced to
an excess of sodium
carbonate used in
treatment for some
other difficulty
where animal or
vegetable oil finds
its way into the
boiler.

DissolvedColloidalSolids
Foaming, deposits in Coagulation & Enters boiler with
Oil & Grease
boiler filtration condensate
Forms are
bicarbonates,
Scale deposits in sulphates, chlorides,
boiler, inhibits heat and nitrates, in that
Hardness, Calcium transfer, and thermal Softening, plus order. Some calcium
(Ca), and Magnesium efficiency. In severe internal treatment in
salts are reversibly
(Mg) cases can lead to boiler.
boiler tube burn soluble. Magnesium
thru, and failure. reacts with
carbonates to form
compounds of low
 15

solubility.

Foaming, carbonates Deaeration of make- Sodium salts are

form carbonic acid up water and found in most
in steam, causes condensate return. waters. They are
Sodium, alkalinity,
condensate return Ion exchange; very soluble, and
NaOH, NaHCO3, Na2CO3
line, and steam trap deionization, acid cannot be removed
corrosion, can cause treatment of make- by chemical
embrittlement. up water. precipitation.
Tolerance limits are
Hard scale if
Sulphates (SO4) Deionization about 100-300ppm
calcium is present
as CaCO3
Priming, or the
passage of steam
Priming, i.e. uneven from a boiler in
delivery of steam "belches", is caused
from the boiler by the concentration
(belching), carryover sodium carbonate,
of water in steam sodium sulphate, or
lowering steam sodium chloride in
Chlorides, (Cl) Deionization
efficiency, can solution. Sodium
deposit as salts on sulphate is found in
super heaters and many waters in the
turbine blades. USA, and in waters
Foaming if present where calcium or
in large amounts. magnesium is
precipitated with
soda ash.
Deposits in boiler, in Most common form
Iron (Fe) and Aeration, filtration,
large amounts can is ferrous
Manganese (Mn) ion exchange.
inhibit heat transfer. bicarbonate.
Silica combines with
many elements to
produce silicates.
Silicates form very
tenacious deposits in
Hard scale in boilers Deionization; lime boiler tubing. Very
and cooling systems: soda process, hot-
Silica (Si) difficult to remove,
turbine blade lime-zeolite
deposits. treatment. often only by fluoric
acids. Most critical
consideration is
volatile carryover to
turbine components.
 16

3 WATER TREATMENT
Water treatment removes constituents through a combination of physical and
chemical means and are known as physiochemical unit processes. [28]

It is performed in two steps:

1. Pretreatment
2. Treatment

3.1 PRETREATMENT [29]

Pretreatment can be classified into four groups: physical, chemical, biological and
electrical strategies. Pretreatment can remove soluble salt (hardness) collides (silt,
Fe, Al, silica) solid (suspended solids and particulate organics) biological material
and dissolved organic material.
.

3.1.1 PRETREATMENT OF WATER PRIOR TO RO-TREATMENT [30]

To control the RO membrane fouling, all the organic, colloidal, and biological
matter needs to be removed from feed water to the RO system. Hence a proper pre-
treatment process capable of producing a substantial reduction in fouling potential of
membrane is very important to the functioning of a RO filtration process.

Conventional pretreatment methods and their limitations

Conventionally disinfection, coagulation, flocculation, sedimentation, and deep bed

filter application are used together as a pretreatment approach after which SDI (silt
density index) measurements are used as a criterion to evaluate the efficiency of the
pretreatment.

However, minute changes occurring in a conventional treatment can have adverse

effect on the RO filtration process. Factors such as chemical overdose, improper
 17

chemical use in pretreatment will result in irreversible fouling, power consumption

and increased cleaning operations.

RO system-pretreatment techniques

Due to these limitations many sea-water reverse osmosis (SWRO) plants are using
membrane filtration such as micro-filtration (MF) and ultra-filtration (UF) as
pretreatment techniques.

Advantages of UF-pretreatment technique over conventional methods

Application of UF as a pretreatment technique results in the usage of fewer

chemicals, less floor space and higher water recovery than conventional methods. It
also eliminates the need for cartridge filter/sludge disposal with similar energy
requirements as conventional pretreatment processes.

3.2 TREATMENT TECHNIQUES [30]

When the pretreatment of the process fluid (water) is efficiently done, its treatment
can now be performed. A list of treatment techniques is given, in which various
chemical and physical techniques are employed for the treatment of the process
fluid, of one is the reverse osmosis technique which is the most effective and energy
efficient technique to be employed.
18
19
 20

4 RO-MASS TRANSFER TECHNIQUE

Reverse Osmosis is a technique employed in mass transfer operations because of the
following reasons or concerns:
 21

 The pressure-driven “transport of water from a solution through a

membrane” is known as reverse osmosis.[31]
 In the reverse osmosis (RO) process, water passes through a membrane,
leaving behind a solution with a smaller volume and a higher concentration
of solutes.[31]
 This is the selective mass-transfer as proposed in “Homogeneous Solution-
diffusion Model”[32] which assumes that both solute and the solvent
dissolves in the upstream face of the membrane then cross through the
membrane by molecular diffusion and are released into the permeate bulk in
contact with the downstream face.[31]
 Membrane separation process:

Figure# 2.
Reverse osmosis systems [33]
 The equilibrium concentrations of components of mixtures often differ
across the boundary between one phase and another as in RO the boundary is
membrane itself.
 These differences can be used to effect separations by the enrichment of one
phase relative to the other, by ‘differential transfer of mass’ of particular
components across the phase boundary.
 The net driving force for mass transfer in reverse osmosis is the difference
between the net applied differential pressure DPa, and the differential
osmotic pressure, DPo, which resists the flow in the desired "reverse"
direction. Therefore it can be described by the standard rate equation, with
the rate of mass transfer being equal to the driving force multiplied by the
appropriate mass-transfer coefficient[32]:
Dw/dt = KA [DPa- DPo]
where dw/dt is the rate of mass transfer, K is the mass transfer coefficient, A
the area through which the transfer is taking place. DP is therefore the
difference in the applied pressure on the solutions at each side of the
membrane and DP is the difference in the osmotic pressures of the two
solutions, as in Fig.2.
 Moreover, membranes used in such techniques also involve mass-transfer in
their formation as ultimate membrane structure results as a combination of
 22

phase separation and mass transfer, variation of the production conditions

giving membranes with different separation characteristics.

5 WHEN WILL BE THE RO IS PREFERRED OVER

OTHER SEPARATION TECHNIQUES [31]:

 Whilst effective product separation is crucial to economic operation in the

process industries, certain types of materials are inherently difficult and
expensive to separate. Important, examples include:

(a)Finely dispersed solids, especially those which are compressible, and which
have a density close to that of the liquid phase, have high viscosity, or are
gelatinous.
(b) Low molecular weight, non-volatile organics or pharmaceuticals and
dissolved salts.
(c)Biological materials which are very sensitive to their physical and chemical
environment.

 Since highly effective and energy efficient.

 Moreover, they potentially offer the advantages of ambient temperature
operation, relatively low capital and running costs, and modular construction.

REVERSE OSMOSIS
[34] Reverse osmosis is a demineralization process that relies on a semi
permeable membrane to effect the separation of dissolved solids from a liquid.
The semi permeable membrane allows liquid and some ions to pass, but retains
the bulk of the dissolved solids.

To understand how RO works, it is first necessary to understand the natural process

of osmosis.

6 OSMOSIS
Osmosis is a natural process where water flows through a semi permeable
membrane from a solution with a low concentration of dissolved solids to a
solution with a high concentration of dissolved solids.
Picture a cell divided into 2 compartments by a semi permeable membrane. This
membrane allows water and some ions to pass through it, but is impermeable to
most dissolved solids. One compartment in the cell has a solution with a high
concentration of dissolved solids while the other compartment has a solution with a
low concentration of dissolved solids. Osmosis is the natural process where water
will flow from the compartment with the low concentration of dissolved solids to the
compartment with the high concentration of dissolved solids. Water will continue to
flow through the membrane until the concentration is equalized on both sides of the
 23

membrane. At equilibrium, the concentration of dissolved solids is the same in both

compartments, there is no more net flow from one compartment to the other.
However, the compartment that once contained the higher concentration solution
now has a higher water level than the other compartment. The difference in height
between the 2 compartments corresponds to the osmotic pressure of the solution that
is now at equilibrium.

Osmotic pressure (typically represented by n (pi)) is a function of the

concentration of dissolved solids.
For example:
 Brackish water at 1,500 ppm TDS would have an osmotic pressure of about
15psi.
 Seawater, at 35,000 ppm TDS, would have an osmotic pressure of about 350
psi.

7 REVERSE OSMOSIS

Reverse osmosis is the process by which an applied pressure, greater than the
osmotic pressure, is exerted on the compartment that once contained the high-
concentration solution. This pressure forces water to pass through the membrane in
the direction reverse to that of osmosis. Water now moves from the compartment
with the high-concentration solution to that with the low concentration solution. Due
to this, relatively pure water passes through membrane into the one compartment
while dissolved solids are retained in the other compartment. Hence, the water in the
one compartment is purified or “demineralized,” and the solids in the other
compartment are concentrated or dewatered.

.
 24

Due to the resistance of the membrane, the applied pressures required to achieve
reverse osmosis are significantly higher than the osmotic pressure.
For example
 For 1,500 ppm TDS brackish water, RO operating pressures can range from
about 150 psi to 400 psi.
 For seawater at 35,000 ppm TDS, RO operating pressures as high as 1,500
psi may be required.

7.1 OBJECTIVES
 Reverse osmosis can be used to either purify water
 Or to concentrate and recover dissolved solids in the feed water (known as
"dewatering").
7.2 BLOCK SCHEMATIC DIAGRAM FOR RO-OPERATION

 Raw water prior to its treatment is fed to three cartridge filters in series for
pretreatment at a flow rate enough for its flow across the filters.
 Since RO membrane is sensitive to TDS removal, any suspended solids and
colloids will damage the membrane. Moreover, these are also undesirable for
the feed pump, hence filters are used to remove any undesired suspended
solids and colloids.
 Because an RO feed pump requires a certain volume and pressure of make-
up water to the suction side of the RO feed pump so as not to cavitate the
 25

pump, Low pressure switch along with the Auto-control-valve is installed

at the outlet of first filter.
 This switch helps in maintaining the suction pressure of influent stream to
RO feed pump as well as for flow across the filters. When somehow the
pressure becomes not sufficient for flow across next filter, low pressure
switch yield signal to the controller, it will further send order to auto control
valve to be closed, this results in pressure built-up at that end thus
maintaining sufficient pressure.
 The pretreated water from the filters is then fed at required operating
pressure to the membrane module (spiral-wound) through the RO-feed
pump. Here Diaphragm booster pump is used which acts centrifugally to
provide the desired operating pressure safely.
 The feed water is then treated through Spirally-wounded flat sheet membrane
resulting in two effluents streams, one permeate and the other
retentate/concentrate.
 Spiral-wound modules allow the efficient packaging of flat sheet membrane in
a convenient cylindrical form. Moreover their other features making the
apparatus efficient will be discussed later under the heading of spiral-wound
modules.
 High pressure switch is situated at the permeate stream to check for
membrane performance i.e.: senses high pressure at that stream and send
information to the controller thus indicating that the membrane efficiency
has lowered due to its damage.
 A Combination valve is installed at the effluent of retentate stream for the
protection of diaphragm booster pump and membrane. It is performing two
functions simultaneously: measure the flow along with controlling it at this
side. Moreover, it is a type of throttling valve which remains partially open
at normal operation so that helps in maintaining the pressure at the feed side
of the membrane. Its throttling action also provide scouring action to the
scales on the membrane thus helps in effective mass transfer across the
membrane.
 Permeate is either stored in the Storage tank or further sent to Taste and
Odor removal unit (if necessary for further purification).

7.3 FLOW MECHANISMS THROUGH RO-MEMBRANES

Following are the two mechanisms through which the feed stream follow through
the membranes:

7.3.1 CROSS-FLOW FILTRATION

In cross-flow filtration, feed water passes tangentially over the membrane surface
rather than perpendicularly to it. Water and some dissolved solids pass through the
membrane while the majority of dissolved solids and some water do not pass
through the membrane. Hence, cross-flow filtration has one influent stream but
yields two effluent streams.
 26

7.3.1.1 Advantage Of Cross Flow

Cross-flow helps to minimize fouling or scaling of the RO membrane. In an effort to
keep the membrane surface free of solids that may accumulate and foul or scale the
membrane, tangential flow across the membrane surface aids in keeping the surface
clean by scouring the surface; minimum flow rates across the membrane surface are
required to effectively scour the surface.

In practice, however, the scouring action of cross flow is not always enough to
prevent all fouling and scaling. Periodically, the membranes will need to be taken
off line and cleaned free of material that has accumulated at the surface.

A simplified block diagram showing how cross-flow RO actually works.

The diagonal line inside the rectangle represents the membrane. This diagram shows
how the influent stream, with an applied pressure greater than the osmotic pressure
of the solution, is separated into two effluent streams. The solution that passes
through the membrane is called permeate or product, and the solution retained by
the membrane is called the concentrate, reject, waste, brine, or retentate. The
flow control valve on the concentrate stream provides the back-pressure needed to
cause reverse osmosis to occur. Closing the valve will result in an overall increase in
pressure driving force, and a corresponding increase of influent water that passes
through the membrane to become permeate.

7.3.2 DEAD-END FILTRATION

Dead end filtration involves all of the feed water passing through the membrane,
leaving the solids behind on the membrane.
 27

Dead end filtration is a batch process. That means that the filter will accumulate and
eventually blind off with particulates such that water can no longer pass through.
The filtration system will need to be taken off line and the filter will need to be
either cleaned or replaced.

7.4 BASIC DEFINITIONS AND TERMS

7.4.1 RECOVERY

“Recovery (referred as “conversion”) is a term used to describe what volume

percentage of influent water is “recovered” as permeate.”
Equation to calculated recovery:
% Recovery = (permeate flow / feed flow) * 100
A system recovery of 75% means that for every 100 gpm influent, 75 gpm will
become permeate and 25 gpm will be retained as concentrate.
 At 75% recovery, the concentrate volume is one-fourth that of the
influent volume. If assumed that the membrane retains all the
dissolved solids, they would be contained in one-fourth of the volume
of influent water. Hence, the concentration of retained dissolved
solids would be four times that of the influent stream. This is called
the "concentration factor."
 At 50% recovery, the concentrate volume would be one-half that of
the influent water. In this case, the dissolved solids would be
concentrated by a factor of two, so the concentration factor would be
2.
Higher recovery results in the need to dispose of less reject water. Higher
recovery also results in lower-purity permeate.
At the influent end of the membrane, the influent concentration is 100 ppm, while
the recovery is 0%, and the membrane passes 2% total dissolved solids (TDS). The
permeate right at this spot would be about 2 ppm. As the influent water passes
across more and more membrane area, more water is recovered. At 50% recovery,
the concentration factor is 2, so the influent water now has a concentration of about
200 ppm. The permeate water at this point would now have a concentration of 4
ppm. At 75% recovery, the concentration factor is 4, so the influent water now has a
concentration of about 400 ppm. The permeate water at this point would have a
concentration of 8 ppm. Hence, higher recovery results in lower product purity.
 28

In practice, the recovery of the RO system is adjusted using the flow control valve
located on the RO concentrate stream .Throttling the valve will result in higher
operating pressure, which forces more water through the membrane as opposed to
down along the feed/concentrate side of the membrane, and results in higher
recovery.
The recovery of an RO system is fixed by the designer.
 Exceeding the design recovery can result in accelerated fouling and scaling
of the membranes, because less water is available to scour the membrane on
the concentrate side.
 Falling below the design recovery will not adversely impact membrane
fouling or scaling, but will result in higher volumes of wastewater from the
RO system.

7.4.2 REJECTION

“Rejection is a term used to describe what percentage of an influent species a

membrane retains.”
For example
98% rejection of silica means that the membrane will retain 98% of the influent
silica. It also means that 2% of influent silica will pass through the membrane into
the permeate (known as "salt passage").
Formula to calculate rejection
% Rejection = [(Cf- Cp)/ Cf]* 100
Cf= influent concentration of a specific component
Cp= permeate concentration of a specific component
Rejection of a particular species is also based on the following characteristics:
 The rejection of multi-valent ions is generally greater than for mono-valent
ions
 Degree of dissociation: the greater the dissociation, the greater the rejection,
for example, weak acids are rejected better at higher PH
 Molecular weight: in general, the greater the molecular weight, the greater
the rejection, for example, the rejection of calcium is marginally better than
the rejection of magnesium.
 Polarity: in general, the greater the polarity, the lower the rejection, for
example, organics are rejected better than water.
 29

 Degree of hydration: in general, the greater the degree of hydration, the

greater the rejection, for example, chloride is rejecter better than nitrate.
 Degree of molecular branching: in general, the more branching, the greater
the rejection, for example, isopropanol is rejected better than normal
propanol.
The rejection of gases is 0%, means that the concentration in the permeate stream
will be the same as it is in the influent and concentrate streams.
7.4.3 SALT PASSAGE

It is essentially the opposite of rejection:

% Salt Passage = 100 - % Rejection
7.4.4 FLUX

“Flux is defined as the volumetric flow rate of a fluid through a given area.”
 In terms of RO: flux is expressed as gallons of water per square foot of
membrane area per day (gfd).
 The flux of water through an RO membrane is proportional to the net
pressure driving force applied to the water.

7.4.5 CONCENTRATION POLARIZATION

The flow of water past an RO membrane is similar to that of the flow of water
through a pipe.
The flow in the bulk solution is convective, while the flow in the boundary layer is
diffusive and is perpendicular to the convective flow of the bulk solution. There is
no convective flow in the boundary layer.
 30

Consider the flow along the surface of a membrane. The same boundary layer forms
as with flow through a pipe. However, with a membrane system, because there is a
net flow out through the membrane, there is convective flow to the membrane, but
only diffusional flow away from the membrane. Since diffusion is slower than
convection, solutes rejected by the membrane tend to build up on the surface and in
the boundary layer. Thus, the concentration of solutes at the membrane surface is
higher than in the bulk solution. This boundary layer is called "concentration
polarization."
Concentration polarization has a negative effect on the performance of an RO
membrane.
 It acts as a hydraulic resistance to water flow through the membrane.
 The buildup of solutes increases the osmotic pressure within the boundary
layer, effectively reducing the driving force for water through the membrane.
 The higher concentration of solutes on the membrane surface than in the bulk
solution, leads to higher passage of solutes than would be predicted by the
feed water concentration.
For example,
Assume that the bulk concentration of silica is 10 ppm, while the concentration at
the membrane surface is 11.5 ppm. If the rejection is 98%, the silica concentration
that would be expected to be in permeate based on the bulk concentration is 0.20
ppm. However, the membrane "sees" 11.5 ppm, so the actual salt passage is 2% of
11.5 ppm, or 0.23 ppm. Actual rejection is still 98%. Apparent rejection is 97.7%.

7.4.6 BETA

"Concentration polarization factor"

“It is the ratio of the concentration of a species at the membrane surface to that in
the bulk solution.”
 The higher the Beta number, the more likely the membranes are to foul
or scale. Since Beta measures the ratio of concentration at the surface to that
in the bulk solution, the higher the beta number, the higher the relative
concentration at the surface. If the concentration at the surface gets high
enough, saturation may be reached and scale will begin to form.
 Beta is a function of how quickly the influent stream is dewatered
through the RO system. If water is removed too quickly from the influent
stream, Beta will increase, as a relatively high volume of dissolved solids is
 31

left behind on the membrane because of the high volume of water that
permeates through the membrane.

7.4.7 FOULING

Membrane fouling is a result of deposition of suspended solids, organics, or

microbes on the surface of the membrane, typically on the feed /concentrate side.
Fouling is increased by high membrane flux and low cross flow velocity both
conditions that increase concentration polarization.
 Higher flux translates into water being removed through the membrane at a
faster rate, leaving behind solids that now accumulate more rapidly in the
concentration polarization boundary layer.
 Cross-flow velocity affects the thickness of the boundary layer. Lower cross-
flow velocity corresponds to a thicker boundary layer. A thicker boundary
layer allows for greater accumulation of solids in the layer, and the solids
spend more time in the layer due to the increased thickness of the boundary
layer, setting up the potential for accelerated fouling of the membrane.
A fouled membrane exhibits two major performance issues:
 Higher than normal operating pressure.
 Higher than normal pressure drop.

7.4.8 SCALING

Scaling of RO membranes is a result of precipitation of saturated salts onto the

surface of the membrane.
 Calcium scales, including carbonate, sulfate, fluoride, and phosphate,
 Reactive silica, which is measured in the RO reject and is a function of
temperature and pH
 Sulfate-based scales of trace metals, such as barium and strontium.
Scaling is increased by high membrane flux and low cross-flow velocity.
 Higher flux brings more solutes into the concentration polarization boundary
layer quicker. If the concentration of the solutes in the boundary layer
reaches saturation, these solutes will scale the membrane.
 32

 Lower cross-flow velocity corresponds to a thicker boundary layer. This

increases the residence time for solute within the boundary layer, increasing
the chance that saturation will be achieved and scale will form.
A scaled membrane exhibits three major performance issues:
 Higher than normal operating pressure
 Higher pressure drop,
 Lower than expected salt rejection

7.5 DESIGN CONSIDERATIONS/FACTORS FFECTING RO

Operating conditions affect the performance of an RO system.

These conditions include:
 Total dissolved solids
 Temperature
 Pressure
 Feed water flow
 Concentrate flow
 Beta
 Recovery
 Flux
 PH

7.5.1 TOTAL DISSOLVED SOLIDS

The total dissolved solids (TDS) concentration affects both the system flux and the
salt rejection of an RO system.
 As feed TDS increases, the driving force for water decreases, due to the
increase in osmotic pressure of the feed. This results in a decrease in system
flux.

 As the driving force for water decreases, the amount of water passing
through the membrane relative to the amount of salt decreases, resulting in a
higher TDS concentration in the permeate.
 33

7.5.2 TEMPERATURE

Temperature influences system flux and rejection performance.

 For every 1°C change in temperature, there is a 3% change in water flux.
This occurs because the lower viscosity of warmer water allows the water to
flow more readily through the membranes.

 Salt rejection decreases slightly with increasing temperature. Salt diffusion

through the membrane is higher at higher water temperature.

Temperature changes are dealt with by adjusting the operating pressure:

 Lower pressure in the warmer summer months.
 Higher pressure in the colder winter months.
 34

7.5.3 PRESSURE

Operating pressure directly affects water flux and indirectly affects salt
rejection.
 Operating pressure directly affects the driving force for water across the
membrane, higher pressure will result in higher flux.

 Salt transport is unaffected by pressure. So, the same amount of salt passes
through the membrane at low or at high feed water pressure. More water has
passed through the membrane at higher pressure, the absolute salt
concentration in permeate is lower, so it appears as if the salt passage
decreases and the salt rejection increases as pressure increases.

7.5.4 FEED WATER FLOW

At higher feed water flow rates, contaminants such as colloids and bacteria that may
be present in the source water, are sent to the membrane more rapidly, resulting in
faster fouling of the membrane. This is why lower flow rates are recommended for
water sources that contain high concentrations of contaminants.

7.5.5 CONCENTRATE FLOW

 At lower concentrate flow rates, good cross-flow velocity is not maintained,

and contaminants, such as colloids and scale-formers, have a much greater
 35

chance of fouling or scaling a membrane. This is because the concentration

polarization boundary layer is thicker at lower cross-flow velocities than it
would be at higher concentrate flow rates.
 The potential for fouling or scaling a membrane can be very high at low
concentrate flow rates.

7.5.6 BETA

Beta is the ratio of the concentration of a species at the membrane surface to that in
the bulk solution
Beta affects both the flux through an RO membrane and the salt rejection.
 The increase in Beta due to concentration polarization at the membrane
surface results in increased osmotic pressure and decrease is water flux and
increase in salt passage.

7.5.7 RECOVERY

 As the recovery increases, the water flux decreases slowly until the recovery
is so high that the osmotic pressure of the feed water is as high as the applied
pressure, in which case, the driving force for water through the membrane is
lost and the flux ceases.

 As the osmotic pressure of the feed /concentrate stream approaches the

applied pressure, the driving force for water is decreased, but the driving
force for salt is unaffected. Less water passes through the membrane relative
to the amount of salt passing through the membrane. Thus, it appears as if
the salt passage increases and salt rejection decreases with increasing
recovery. Salt rejection becomes 0% at about the same time that the flux
ceases.
 36

7.5.8 FLUX

Flux is affected by several operating variables:

 Flux is directly proportional to operating pressure.
 Flux is directly proportional to water temperature.
 Flux decreases slightly as recovery increase until the osmotic pressure of the
feed water equals the driving pressure, at which point productivity ceases.
 Flux decreases with increasing feed concentration of dissolved solids.
 Flux is relatively constant over a range of pH, although for some newer
polyamide membranes, flux is also a function of pH.

8 MEMBRANE [35]
“Membrane is thin interphase that restricts the passage of different components in a
specific mode and over a wide range of particle sizes and molecular weights, from
ions to macromolecules.”

The efficiency of a membrane is determined by two parameters:

 Permeability(the rate at which a given component is transported through the

membrane)
 Selectivity(the ability to separate in specific way a given component from
others)

The transport of different species through membrane is a non-equilibrium process,

and separation of the different components is due to the difference in their transport
rate.

Reverse osmosis membranes are characterized by a high degree of semi-

permeability, high water flux, mechanical strength, chemical stability and
economically acceptable cost. [36]
 37

8.1 MODULES [37]

Membrane can have two different configurations:

 Tubular
 Flat sheet

8.1.1 TUBULAR MODULES:

 38

8.1.2 FLAT SHEET MODULES:

8.1.2.1 Spiral Wound Module [35]:

Is utilized in the apparatus, under consideration, used in laboratory, its general
configuration is detailed as:

They consist in an arrangement of two rectangular membranes placed back to back

and sealed on three sides. They are rolled around a collector tube connected to the
fourth side which remains open. The solution to be treated is brought to one end of
this cylinder and the product circulates between both membranes to the collector
tube. Following figure shows the general flow pattern:
 39

8.1.3 COMPARISON OF CHARACTERISTICS OF VARIOUS MODULES

[35]

8.2 GENERALLY USED MEMBRANES

8.2.1 CELLULOSE ACETATE MEMBRANES [37]

 Lower Cost than Thin Film Membranes.

 Typical salt rejection of 96%.
 Typical operating pressures of 400 PSI.
 Optimum pH operating range of 4.8to 6.5.
 Good Chlorine Tolerance.

8.2.1.1 Characteristics of Cellulose Acetate RO Membranes: [34]

 40

8.2.2 THIN FILM COMPOSITE MEMBRANES: [37]

 More expensive than cellulose acetate membranes

 Typical salt rejection of 97 to 99%
 Typical operating pressures of 200 PSI
 Wide pH operating range of 2 -10
 Very Low Chlorine Tolerance
 Less susceptible to compaction due to lower PSI

8.2.2.1 Characteristics of Polyamide Membranes [34]

 41

8.3 FOULING FACTORS AND METHODS TO AVOID:

[38]
 42

9 APPLICATIONS [34]:
 Desalination of seawater and brackish water for potable use.
 Generation of ultrapure water for the microelectronics industry.
 Generation of high-purity water for pharmaceuticals.
 Generation of process water for beverages (fruit juices, beer, bottle water).
 Processing of dairy products.
 Concentration of corn sweeteners.
 Waste treatment for the recovery of process materials such as metals for the
metal finishing industries, and dyes used in the manufacture of textiles.
 To purify water for use as boiler makeup to low- to medium-pressure boilers, as
the product quality from an RO can directly meet the boiler make-up
requirements for these pressures.

10 EXPERIMENTAL ANALYSIS [39]

10.1 PROCEDURE:
1. Collect the sample of different types of water like distilled water, tap
water and filtered water in different sample bottles.
2. Switch on the reverse osmosis plant to collect the sample of reverse
osmosis water.
3. Insert pH meter, conductivity meter and TDS meter to determine pH,
conductivity and TDS in different samples of water.
4. Keep on running the RO plant and also keep on taking different samples
after a specific interval of time and check its properties.
5. Note down all the readings in the table and compare what is the
difference.
6. Also note what the effect of time on RO water properties.
7. Draw the graphs between Time VS TDS, conductivity and pH in case of
reverse osmosis water.

10.2 OBSERVATIONS AND CALCULATIONS:

Room temperature = ᵒC

10.2.1 OBJECTIVE 1:

To study and compare the properties of tap water, reverse osmosis

water and distilled water.

Tap Water Distilled Water RO Water

TDS Conductivity pH TDS Conductivity pH Time TDS Conductivity pH
(ppm) (mho) (ppm) (mho) (min) (ppm) (mho)
 43

In addition to this, following objectives can also be achieved by performing further

observations and calculations:

10.2.2 OBJECTIVE 2:

Same calculations as mentioned above can also be performed for “The Purification
of Water for Drinking Purposes"

10.2.3 OBJECTIVE 3:

To Check the Performance of RO-apparatus

10.2.4 OBJECTIVE 4:

TO Study and Compare the RO Feed Water, Permeate and Retentate

RO WATER ANALYSIS

NO. Feed Permeate Retentate

of
Obs TDS Conductivity p Time TDS Conductivity p TDS Conductivity p
(ppm) (mho) H (sec) (ppm) (mho) H (ppm) (mho) H
.

10.2.5 OBJECTIVE 5:

To study the effect of pressure on RO performance by qualitative

analysis of permeate and retentate.

RO WATER ANALYSIS

NO. Operatin permeate retentate

of g
Obs pressure TDS Conductivity pH TDS Conductivity pH
(ppm) (mho) (ppm) (mho)
.
 44

10.3 RESULTS AND DISCUSSIONS:

The experiment is performed on the RO apparatus in the Mass Transfer Lab,

Chemical Engineering Department, ciit Lahore for the qualitative comparison of Tap
Water, Reverse Osmosis Water, and Distilled Water.
Following results were obtained during the experiment performed under the
observation of Muhammad Abdul Qyyum as the resource person:

Room temperature = 25 ᵒC

10.3.1 Comparison of Properties of Various Types of Water

No. Tap Water Distilled Water RO Water

of
Obs TDS Conductivity pH TDS Conductivity pH Time TDS Conductivity pH
. (ppm) (mho) (ppm (mho) (sec) (ppm (mho)
) )
1- 370 56 5.9 1 1.6 5.7 573 133 19.6 5.0

2- - - - - - - 600 157 23.3 5.4

 It is clearly seen from the readings obtained that the distilled water has the
least TDS and conductivity with a pH 5.7.
 Although the distilled water should have zero TDS and correspondingly the
conductivity, but we had a slight increase in the values, the possible reasons
for a slight increase in our values may be the human error while taking the
readings through respective meters and/or may be due to the in-accuracy of
the instruments used.
 In comparison to distilled water, tap water as well as RO water should have
greater values for corresponding parameters, and we have obtained the same
results experimentally as well.
 Tap water fed to the RO apparatus resulted in the decrease in the values of its
prescribed parameters as expected from the RO system.
 The values for the RO water suggest that the conductivity of the water
decreases along with the TDS removal through RO membrane since it is a
function of TDS.
 Moreover, the pH value of the RO water has been lowered from the feed pH.
The reason is the increase acidic nature of the permeate water due to the
presence of CO2.
 45

In addition to these readings, retentate reading was also obtained so that one can
have better understanding of the performance of the apparatus as well as to
examined experimentally the how the RO-system works.

10.3.2 RO Water Analysis

RO WATER ANALYSIS

NO Raw Water Permeate Retentate

. of Time
Obs TDS Conductivity pH (sec) TDS Conductivity pH TDS Conductivity pH
. (ppm) (mho) (ppm (mho) (ppm (mho)
) )

1- 370 56 5.9 573 133 19.6 5.0 341 58.7 5.9

 Above table shows the comparison of various parameters of Raw water,

permeate and the retentate.
 It has been shown that the raw water TDS got distributed in the two effluent
streams, permeate and the retentate as per conditions of the process.
 Permeate is obtained with minimum amount of TDS while the membrane
rejecting remaining TDS to the retentate stream as concentrate.
 As a result of this distribution of TDS over the two streams, the conductivity
of the two streams changes accordingly.
 Now as concerning with the pH, results show that the pH of permeate has
been lowered from the feed water pH, while the retentate pH remained same
as it would be.
 The reason for the low pH of the permeate is the presence of CO2 which also
passes through the membrane resulting in an increase acidic nature of the
permeate thus yielding low pH.
 46

11 REFERENCES:
1. Salil K. Ghosal, Siddhartha Datta, shyamal K sanyal. Introduction to
Chemical Engineering.Page#218,219
2. A. P. Sinha, Parameswar De. Mass Transfer: Principles and Operations.
Page#256
3. Janusz Pawliszyn. Applications of Solid Phase Micro extraction. Page#95
4. AK Srivastava and PC Jain.Chemistry. Volume (1 and 2).Page#393
5. Xiao Dong Chen, Arun S. Mujumdar.Drying Technologies in Food
Processing. Page#113
6. Nicholas P Cheremisinoff. Handbook of Chemical Processing Equipment.
Page#94
7. Lawrence K. Wang, Yung-Tse Hung, Nazih K. Shammas. Advanced
Physicochemical Treatment Processes. Page#567
8. Evangelos Tsotsas, Arun S. Mujumdar. Modern Drying Technology,
Computational Tools at Different Scales. Page#92
9. Nirali Prakashan.Mass Transfer-II.Chapt 2
10. Nicholas P. Cheremisinoff.Handbook of Water and Wastewater Treatment
Technologies. Page#401
11. Fergus G. Priest, Graham G. Stewart. Handbook of Brewing.Second Edition.
Page#129
12. R.D. Noble, S.A. Stern. Membrane Separations Technology: Principles and
Applications. Page#230
13. H Strathmann.Ion-Exchange Membrane Separation Processes.Page#28
14. Andrew T. Weil.Natural Health, Natural Medicine: The Complete Guide to
Wellness and Self-Care for Optimum Health.
15. Sourcebook of Alternative Technologies for Freshwater Augmentation in
West Asia. Page #161
16. J.A. Howell. The Membrane Alternative: Energy Implications for Industry:
Watt Committee.Page#56.
17. Jack Watson .Separation Methods for Waste and Environmental
Applications.Page#329
18. Kerry J. Howe, David W. Hand, John C. Crittenden, R. Rhodes Trussell,
George Tchobanoglous.Principles of Water Treatment. (8.1 topic)
19. Dennis R. Heldman, Richard W Hartel .Principles of Food
Processing.Page#154
20. Takeshi Matsuura .Synthetic Membranes and Membrane Separation
Processes.Page#3
21. M J Lewis .Physical Properties of Foods and Food Processing Systems.
Page#441
 47

22. Hidenao Fukuyama, Denis Le Bihan.Water: The Forgotten Biological

Molecule. Penthouse level, suntec tower 3 8 temasek boulevard Singapore:
Pan Stanford Publishing.30-Nov-2010.Page#10.
23. Zahid Amjad.The science and technology of industrial water treatment.
Alliance House, 12 Caxton Street, London SW1H 0QS, UK: IWA
Publishing.2010.Pag#3
24. Carl R. Branan.Rules Of Thumbs For Chemical Engineers.4th edition.30
Corporate Drive,Suite 400,Burlington,MA 01803,USA.Gulf professional
publishing.2005.page#161-162
25. http://housewares.about.com/od/glossary/g/Potable-Water-Definition.html
26. http://www.corrosion-doctors.org/Corrosion-by-Water/Types-of-
water.htm.
27. ‘Water treatment handbook’ Vol. 1-2, Degremont, 1991
‘Industrial water conditioning’, BeltsDearborn, 1991
http://www.thermidaire.on.ca/boiler-feed.html
28. John c. Crittenden, Rhodes Trussell, David W. Hand, Kerry J. Howe, George
tchobanoglous. Water treatment principles and design. Edition 3. Hoboken,
New Jersey: John Wiley & Sons, inc.2012.
29. KaustubhaMohanty, Mihir K. Purkait.Membrane Technologies and
Applications.Page#168
30. Isabel C. Escobar, Andrea Schäfe.Sustainable Water for the Future: Water
Recycling versus Desalination. Sustainability Science And
Engineering.Volume#2.Redarweg 29 , Amsterdam, the Netherlands Linacre
house,Jordanhill,oxford OX2 8DP, UK.2010
31. J.M. Coulson, J.F.Richardson, J.H. Harker, J.R. Backhurst.Chemical
Engineering: Particulate Technology and Separation Processes.Volume
2,5th Ed.
32. Zeki Berk.Food Process Engineering And Technology. Professor (Emeritus)
Department of Biotechnology and Food Engineer TECHNION Israel
Institute of Technology. Israel
33. R.L. Earle with M.D. Earle. Unit Operations in Food Processing. Web
Edition, 2004.Publisher: The New Zealand Institute of Food Science &
Technology (Inc.).
34. Jane Kucera.Reverse Osmosis: Design, Processes, and Applications for
Engineers. Scrivener Publishing: 3 Winter Street, Suite 3 Salem, MA
01970.2010
35. Enrico Drioli, Efrem Curcio and Enrica Fontananova. Mass Transfer
Operation-Membrane Separations: Chemical Engineering and Chemical
Process Technology.Institute on Membrane Technology, ITM-CNR, C/O
Dept. Of Chemical Engineering and Materials, University Of Calabria, Italy.
 48

36. C.S. Slater, J.D. Paccione.ChE-laboratory: A reverse osmosis system for an

advanced separation process laboratory. Manhattan College.Riverdale,NY
10471.page#139
37. Engr. Muhammad Abdul Qyyum. Reverse Osmosis: An Alternative to ion-
exchange. Department of Chemical Engineering, ciit Lahore.
38. Lawrence K. Wang, Jiaping Paul Chen, Yung-Tse Hung, Nazih K.
Shamma.Membrane and Desalination Technologies.
39. Engr. Ahmed Ali Khan. Lab Manual: Chemical Engineering Mass Transfer
Operations. COMSATS Institute Of Information Technology, Lahore
Campus: Department Of Chemical Engineering

View publication stats