D.Mishra
Dy. Manager(Chem.)
NTPC-Sipat
dileepmishra@ntpc.co.in
94258-23647
Impurities in raw water
and
their effects
sources of raw water
Water treatment depends on the water source:
Three choices:
Surface water
Groundwater
Groundwater under the direct influence of surface
water (GWUDI)
The definition of the last source (GWUDI) is groundwater that has physical evidence of surface water
contamination (e.g., insect parts, high turbidity), or contains surface water organisms (e.g., cryptosporidium,
giardia), or has chemical water quality parameters similar to surface water (e.g., T, conductivity, TDS, pH, color).
Variation In Raw Water Quality
Geographical
Seasonal
Contaminants In Raw Water
•Suspended particles
•Dissolved inorganic salts
•Dissolved organic compounds
•Micro-organisms
•Pyrogens
•Dissolved gases
Suspended particles
•Silt, pipe-work debris, colloids.
Determination
•Fouling index
•Turbiditimetry
Dissolved In-organics
•Calcium & magnesium salts.
•Co2 (carbonic acid).
•Sodium salts.
•Silicates.
•Ferrous and ferric compounds.
•Chlorides.
•Aluminum.
•Phosphates.
•Nitrates.
Measurement
•TDS
•Water conductivity x 0.7
Dissolved Organics
•Decay of vegetable matter (humic and fulvic acids)
•Farming, paper making, and domestic & industrial wastes.
Measurement
•KMno4 test
•COD
•TOC
Micro-organisms
•Amoebae
•Bacteria
•Paramecia
•Rotifers
•Diatoms
•Algae
•Pyrogens
•Cellular fragments of bacterial cell walls (fever causing).
Dissolved gases
•Oxygen
•Carbon dioxide
Impurities, their effects and means of treatment
S.N
o.
Constituent
Chemical
formula
Effects
Treatment
1.
Turbidity
Noneexpressed in
analysis as
units (NTU).
Imparts unsightly appearance to water.
Deposits in water lines, process
equipments etc., Interferes with most
process uses.
Coagulation, settling, and
filtration.
2.
Hardness
Ca and Mg
salts
expressed as
CaCO3.
Scaling in heat exchange equipments,
boilers, pipelines, etc.
Softening, Demineralization,
Internal boiler water treatment.
3.
Alkalinity
HCO3, CO3,
and OH
expressed as
CaCO3.
Foaming and carryover of solids with
steam. Embrittlement of boiler steel.
HCO3 and CO3 produce CO2 in steam
leading to corrosion in condensate lines.
Lime and lime-soda softening.
Acid treatment. H-zeolite
softening. Demineralization.
Dealkalization by anion exchange.
4.
Free mineral
acids
H2SO4, HCl,
etc. expressed
as CaCO3.
Corrosion.
Neutralization with alkalies.
Impurities, their effects and means of treatment
5.
Carbon dioxide
CO2
Corrosion in water lines and particularly
steam and condensate lines.
Aeration. Deaeration.
Neutralization with alkalies.
6.
pH
H-ion
concentration.
pH = - log
(H+)
pH varies according to acidic or
alkaline solids in water. Most natural
waters have a pH of 6 to 8.
PH can be increased by alkalies
and decreased by acids.
7.
Sulphate
SO4 2-
Adds to solids content of water. With Ca
forms CaSO4 scale.
Demineralization.
8.
Chloride
Cl-
Adds to solids content and increases
corrosive character of water.
Demineralization.
9.
Nitrate
NO3-
Adds to solids content.
Demineralization.
Impurities, their effects and means of treatment
S.No
.
Constituent
Chemical
formula
Effects
Treatment
10.
Fluoride
F-
Cause of mottled enamel in teeth. Used
for dental decay. Not significant
industrially.
Adsorption with Ca(OH)2,
Mg(OH)2, Ca3(PO)4, or bone black.
Alum coagulation
11.
Sodium
Na+
Adds to solids content of water. When
combined with OH-, causes corrosion in
boilers.
Demineralization.
12.
Silica
SiO2
Scale in boilers and CW systems.
Deposition on turbine blades.
Hot process removal by Mg salts.
Strong base anion exchange resins
in conjunction with
demineralization.
13.
Iron
Fe2+, Fe3+
Deposits in water lines, boilers etc.
Aeration, Coagulation and
filtration. Lime softening, Cation
exchange.
14.
Manganese
Mn2+
Deposits in water lines, boilers etc.
Aeration, Coagulation and filtration.
Lime softening, Cation exchange.
15.
Aluminum
Al3+
Usually present as a result of floc
carryover from clarifier. Deposits in CW
system and complex boiler scales.
Improved clarifier and filter
operation.
16.
Oxygen
O2
Corrosion of water lines, heat exchange
equipment, boilers, return lines, etc.
Dearation. Sodium sulphite.
Hydrazine. Corrosion inhibitors.
17.
Hydrogen
sulphide
H2S
Causes rotten egg odour. Corrosion.
Aeration. Chlorination. Strong basic
anion resin.
18.
Ammonia
NH3
Corrosion of Cu and Zn alloys.
Cation exchange. Chlorination.
Dearation.
Impurities, their effects and means of treatment
S.N
o.
Constituent
Chemical
formula
Effects
Treatment
19.
Dissolved
solids
None
Foaming in boilers.
Lime softening. Cation exchange.
Demineralization.
20.
Suspended
solids
None
Deposits in heat exchange
equipments, boilers, water lines etc.
Coagulation, settling, filtration.
Types of Water Treatment Methods
 Primary treatment
 Purpose: To remove settable and floatable solids
 Method: screening, grit removal, primary sedimentation
 Secondary treatment
 Purpose: To aerobically and biologically remove biodegradable organic
matter
 Method: activated sludge, trickling filter, rotating biological contactors
 Tertiary (advanced) treatment
 Purpose: To further remove SS, dissolved organics (refractory
compounds) and inorganics (N, P nutrients)
 Method: activated carbon, nitrification / denitrification
Water Treatment Chemistry
16
Types of Water Treatment Methods
 Based on contaminants to be removed:
 Suspended solids: sedimentation, coagulation/flocculation, filter
 Biodegradable organics: activated sludge, trickling filter
 Volatile organics: air stripping, carbon adsorption
 Pathogens: disinfection (Cl2, O3, UV)
 Nutrients (N): nitrification/denitrification, NH3 stripping (p.252)
 Nutrients (P): precipitation, biological removal, adsorption (Al2O3)
 Refractory organics: carbon adsorption, O3/UV radiation
 Hardness (Ca2+, Mg2+), heavy metals: precipitation, ion exchange,
membrane processes, chelation (sequestion)
 Grease: flotation, biological processes
 Dissolved solids: ion exchange, membrane processes
Water Treatment: Selected Topics
 Removal of suspended solids
 Coagulation / Flocculation
 Removal of hardness
 Water Softening
 Removal of pathogenic bacteria
 Disinfection
Surface water & GWUDI generally requires the most treatment as shown in the
following schematics.
Groundwater requires much less treatment:
Typical Water Treatment Plant
Surface
Water
Primary
Settling
Coagulation/ Secondary
Flocculation Settling
Filtration
Disinfection
Clean water
to consumer
Sludge
Ground
Water
Aeration
Sludge
Primary
Settling
Coagulation/ Secondary
Flocculation Settling
Filtration Disinfection
Clean water
to consumer
Sludge
Sludge
Removal of Solids:
 Solids in water and wastewater:
 Dead animals, plant biomass, food debris
 Soil particles (clay, sand, etc.)
 Colloidal particles (humic substances)
 Bacterial cells, algal cells, virus
 Sludge
 Primary methods for the removal of solids
 Screening: physical process
 Filtration: physical process
 Settling: physicochemical processes including coagulation
and flocculation
Water Treatment Chemistry
22
Coagulation for the Removal of Solids:
What? Why? How?
 What? Coagulation involves the reduction of electrostatic
repulsion such that colloidal particles of identical materials may
aggregate.
 Why? Colloidal particles are prevented from aggregating by
electrostatic repulsion of the electrical double layers. They are
small in size and very stable in water.
 How? By the addition of coagulants followed by flocculation .
Treatment of Water
1.
Clarification
2.
Filtration
3.
Softening or Demineralisation
Clarification
Pre- Treatment of water

Mixing of chemicals with water

Coagulation and flocculation

Sedimentation

Filtration
Coagulants
1.
Aluminium Sulphate, Sodium Aluminate
2.
Iron sulphate
3.
Poly electrolytes (long chain amides)
4.
Poly Aluminium Chloride ( PAC )
Factors affecting coagulation
1.
pH ( 5.5 – 8.0 ) for Al2(SO4)3
2.
Temperature (30- 400C )
3.
Time
Clariflocculator:
Chlorine
Lime Flash
Alum
Mixer
Flocculation
Clarification
Clarified
water to
filters
Raw
water
Water quality at Clarifier outlet
Turbidity - <20 NTU
Residual Chlorine
pH
-
- 5.5 to 8.0
0.2 ppm
Sludge
settling
pond
Filtration
Adsorption
Small particles attached
to media
Mechanical
Large particles trapped
between media
Filtration
Filtration is the removal of the solid particles from water by
passing it through a filtering medium. Filtration is usually a
mechanical process does not remove dissolved solids.
Filters used in Water Treatment are mainly of two types.
1. Pressure Filters
2. Gravity filters

Pressure filters are in closed, round steel shells and function
with the pressure of the incoming water.

Gravity filters are in steel, wood or concrete containers that are
open at the top and function at atmospheric pressure.
Filter Media

Theoretically any inert granular material can be used for
filtration.

Quarts sand, Silica sand, anthracite coal, garnet may be used
for filtration.

Silica sand and anthracite are the types of filter media which
are commonly used.
Filter medium layers in GSF
1st layer - 50 mm X 37 mm gravel
2nd layer - 37 mm X 12 mm gravel
3rd layer – 12 mm X 6 mm gravel
4th layer – 6 mm X 2.5 mm grit
5th layer – 0.35 mm X 0.5 mm sand
Gravity Sand Filter
Gravity Sand Filter
Clarified
water from
clarifier
IN
5th layer
4th layer
3rd layer
2nd layer
1st layer
For back washing of the
GSF water is passed
through filter in reverse
direction
OUT
Gravity filters
Normal operation
Influent
Surface washers
Backwash trough
Optional cap
Anthracite
Iron (Fe) removal
Filter media
Barrier media
Air Gap
To waste
Dispersion media
Underdrain system
To clearwell
Gravity filters
Backwash operation
Influent
Surface washers
Backwash trough
Air Gap
Media
expansion
Optional
cap
of at
least 20%
Anthracite
Filter media
To waste
Barrier media
Dispersion media
Underdrain system
Backwash water
To clearwell
Pressure filters
Vertical
Horizontal
Removal of Hardness (Ca2+, Mg2+):Water
Softening
 Hardness is an important water quality parameter in
determining the suitability of water for domestic and
industrial uses
 Hard waters require considerable amounts of soap to produce
foam
 Hard waters produce scale in hot-water pipers, heaters and
boilers
Ca2+ + 2HCO3-  CaCO3 (s) + CO2 (g) + H2O
 Groundwater is generally harder than surface water
 Principal cations causing hardness and the major anions
associated with them (in decreasing order of abundance in
natural waters)
 Cations: Ca2+, Mg2+, Sr2+, Fe2+, Mn2+
 Anions: HCO3-, SO42-, Cl-, NO3-, SiO32-
Water Treatment Chemistry
36
Softening process
 Hard water is usually defined as water which contains a high
concentration of calcium and magnesium ions.
 Measurements of hardness are given in terms of the calcium
carbonate equivalent.
 Hardness generally enters groundwater as the water percolates
through minerals containing calcium or magnesium.
 The most common sources of hardness are limestone (which
introduces calcium into the water) and dolomite (which
introduces magnesium.)
 Softening is the removal of hardness from water.
Softening process
 However, hard water is problematic for a variety of reasons.
1.Hard water makes soap precipitate out of water and form a scum,
such as the ring which forms around bathtubs.
2. Hard water may also cause taste problems in drinking water.
3. Deposition of scales on heat transfer surfaces.
Types of Hardness
 As mentioned above, hardness in water is caused by a
variety of divalent cations, primarily calcium and
magnesium.
 These cations have a tendency to combine with anions
(negatively charged ions) in the water to form stable
compounds known as salts.
 The type of anion found in these salts distinguishes
between the two types of hardness - carbonate and
noncarbonate hardness.
Types of Hardness
Carbonate hardness compounds
Non-carbonate hardness compounds
Calcium carbonate (CaCO3)
Calcium sulfate(CaSO4)
Magnesium carbonate (MgCO3)
Magnesium sulfate (MgSO4)
Calcium bicarbonate (Ca(HCO3)2)
Calcium chloride(CaCl2)
Magnesium bicarbonate (Mg(HCO3)2)
Magnesium chloride (MgCl2
Types of Hardness
 Carbonate hardness is sometimes called temporary hardness




because it can be removed by boiling water.
Ca2+ + 2HCO3-  CaCO3 + CO2 + H2O
Noncarbonate hardness cannot be broken down by boiling the
water, so it is also known as permanent hardness. Noncarbonate
hardness cations are associated with SO42-, Cl- and NO3-.
When measuring hardness, we typically consider total hardness
which is the sum of all hardness compounds in water, expressed
as a calcium carbonate equivalent.
Total hardness includes both temporary and permanent hardness
caused by calcium and magnesium compounds.
Total hardness = Carbonate hardness + Noncarbonate hardness
Problems Due to Hardness
Carbonate and noncarbonate hardness can cause different
problems.
Carbonate hardness is the most common and is responsible
for the deposition of calcium carbonate scale in pipes and
equipment. The equation below shows how this deposition
is formed in the presence of heat:
Ca(HCO3)2
CaCO3 + H2O + CO2
In addition to the scale (calcium carbonate) produced,
carbon dioxide resulting from this reaction can combine
with water to give carbonic acid which causes corrosion of
iron
or
steel
equipment.
Water Hardness
 Hardness expressed in mg/L as CaCO3
mg/L CaCO3 Degree of hardness
0-75
75-150
150-300
300 up
Soft
Moderately hard
Hard
Very hard
 Methods of determination
 Calculation (see example)
Hardness (mg/L) as CaCO3 = M2+ (mg/L) x 50 / EW of
M2+
 EDTA titrimetric method
M2+ + Eriochrome Black T (blue)  (M · Eriochrome
Black T)complex (wine red)
 Water softening is needed when hardness is above 150-200
mg/L; Hardness 50-80 is acceptable in treated water
Water Treatment Chemistry
43
Water Softening Methods
 Ion exchange
 Reverse osmosis
 Coagulation /flocculation (most commonly used):
Ca2+, Mg2+  CaCO3 (s), Mg(OH)2 (s)
 lime-only process: when Ca2+ is present primarily as
“bicarbonate hardness”
 lime-soda [Ca(OH)2-Na2CO3] process: when bicarbonate
is not present at substantial level
Lime-Soda Process for Water Softening:
Chemical Reactions Involved
 Lime to remove Ca2+ in the form of natural alkalinity
Ca(HCO3)2 + Ca(OH)2  2CaCO3 + 2H2O
 Lime to remove Mg2+ in the form of natural alkalinity
Mg(HCO3)2 + Ca(OH)2  MgCO3 (soluble) + CaCO3 +
2H2O
additional lime must be added to remove MgCO3
MgCO3 + Ca(OH)2  CaCO3 + Mg(OH)2
 Mg2+ hardness in the form of a sulfate requires both lime and soda
ash
MgSO4 + Ca(OH)2  CaSO4 + Mg(OH)2
CaSO4 + Na2CO3  CaCO3 + Na2SO4
 CO2 in the water will also consume lime
CO2 + Ca(OH)2  CaCO3  + H2O
Lime Softening
 The goal of all of these reactions is to change the calcium
and magnesium compounds in water into calcium
carbonate and magnesium hydroxide.
 These are the least soluble calcium and magnesium
compounds and thus will settle out of the water at the
lowest concentrations. For example, calcium carbonate
(which is essentially the same as limestone) will settle out
of water at concentrations greater than 40 mg/L.
Removal of Non-carbonate Hardness
 In many cases, only the carbonate hardness needs to be
removed, requiring only the addition of lime.
 However, if noncarbonate hardness also needs to be removed
from water, then soda ash must be added to the water along
with lime.
 Each non-carbonate hardness compound will have a slightly
different reaction.
 The lime first reacts with the magnesium sulfate, as shown
below:
MgSO4 + Ca(OH)2
Mg(OH)2 + CaSO4
Removal of Non-carbonate Hardness
 The resulting compounds are magnesium hydroxide, which
will precipitate out of solution, and calcium sulfate.
 The
calcium sulfate
CaSO4 + Na2CO3
then reacts with soda
CaCO3 + Na2SO4
ash:
 The calcium carbonate resulting from this reaction will settle
out of the water.
 The sodium sulfate is not a hardness-causing compound, so
it can remain in the water without causing problems.
Lime-Soda [Ca(OH)2-Na2CO3] Process:
Recarbonation by bubbling CO2 after softening
 Recarbonation is usually required after lime-soda process
 Why?
 To prevent super-saturated CaCO3 (s) and Mg(OH)2 (s)
from forming harmful deposits or undesirable cloudiness
in water at a later time
CaCO3 (s) + CO2 + H2O
Ca2+ + 2HCO3MgCO3 (s) + CO2 + H2O
Ca2+ + 2HCO3 To neutralize excessively high pH caused by Na2CO3
OH- + CO2
HCO3-
Re-carbonation
 The reactions which remove carbonate and noncarbonate hardness
from water require a high pH and produce water with a high
concentration of dissolved lime and calcium carbonate.
 The high pH would cause corrosion of pipes and the excess
calcium carbonate would precipitate out, causing scale.
 So the water must be re-carbonated, which is the process of
stabilizing the water by lowering the pH and precipitating out
excess lime.
 It is achieved by pumping carbon dioxide into the water. Excess
lime reacts with carbon dioxide in the reaction shown below,
producing calcium carbonate:
Ca(OH)2 + CO2
CaCO3 + H2O
Lime-Soda Softening
Lime and/or Soda Ash
Hard Water
Mixing
Flocculation
CO2
Sedimentation
Soft Water
Re-carbonation
Sludge
Sedimentation
Chemicals Used in Lime Softening
(Types of Lime)
 The lime used for softening comes in two forms
a) Hydrated lime (Ca(OH)2) is also known as calcium hydroxide
or slaked lime
b)Quicklime. (CaO), also known as calcium oxide or unslaked
lime
Both types of lime soften water in the same way, but the
equipment required for the two types of lime is different.
Other Methods: Removal of Dissolved Inorganics &
Organics
 Inorganics
 Distillation
 Membrane process

Electrodialysis

Ion exchange

Reverse osmosis
 Filtration

Nanofiltration

Ultrafiltration

Microfiltration
 Organics
 Adsorption


Activated carbon (AC)
 PAC (powered)
 GAC (granulated)
Synthetic polymer
 Oxidation



O3
H2O2
O2
Bacteria
 Coliform Bacteria
 Coliform bacteria are used as an indicator organism
 If present, means that disease-causing organisms may also be
present
 E. coli bacteria are a subset of Total Coliform bacteria come
from human and animal digestive systems – means that fecal
matter is in the water
 Iron-, Manganese- and Sulfur-reducing bacteria
 Nuisance bacteria – can produce stains, odors, ‘slime’
 Not a health risk
Disinfection:
Killing of Pathogenic Bacteria in Water
 Disinfection is typically the last step in a water / wastewater
treatment system
 Residual chlorine is needed in distribution system after water
/ wastewater treatment
 In addition to disinfection, chlorine also has the following
functions:
 taste and odor control as an oxidizing agent
 oxidation of Fe2+ and Mn2+ in groundwater
 ammonium removal in domestic waste treatment
 slime, biofouling control; control of sludge bulking
Water Treatment Chemistry
55
Types of Disinfection
 Gaseous Cl2
 Most commonly used
 Advantage: provide residual chlorine for the protection




from bacterial growth in distribution system
 Disadvantage: The formation of disinfection by-products
(trihalomethanes) presents a health risk
Chlorine dioxide (ClO2):
 No disinfection by-products such as trihalomethanes
Ca(ClO)2:
 Safer than Cl2
Ozone
UV
Chemistry of Chlorine in Water
 Cl2 + H2O  H+ + Cl- + HOCl
 HOCl is a weak acid with Ka = 4.5x10-4 (HOCl == H+ + OCl-)
 HOCl and OCl- are free available chlorine which are very
effective in killing bacteria
 Small amount of ammonium (NH4+) in water is desired
 Chloramine: NH2Cl, NHCl2, NCl3
 Chloramines (combined available chlorine) are weaker
disinfectants than free available chlorine but are desired residual
chlorine to be retained in water distribution system
 Excessive amount of ammonium (NH4+) in water is undesirable
because it consume excess demand of Cl2
 Extra chlorine may be removed by SO2 , a process called
dechlorination:
SO2 + HOCl + H2O  Cl- + SO42- + 3H+
De-Mineralisation of Water
Ion exchange
Reverse osmosis
Electro-dialysis
Ion- exchange resin
 Ion exchange material are synthetic resin made by polymerization
of styrene & divinyl benzene. Major portion is styrene (80-92%)
& minor portion is divinyl benzene (8-20%). The dvb acts as a
crosslink to hold the long chain.
Ion exchange materials
Ion exchange is reversible inter-change of ions between a solid
and liquid in which there is no permanent change in the structure
of the solid i.e. ion exchange resin.
Ion exchange procedure is used in water softening and deionization.
It also provides a method of separation that is useful in many
chemical processes like separation of lanthanide’s.
The utility of ion exchange resin rests on its ability to get
regenerated so that these can be reused again and again.
Structure of ion exchange resins
Matrix: The basic polymeric structure(or the solid support) for ion
exchange resins is called matrix.
Functional Groups: The acidic/basic groups/sites attached to three
dimensional co-polymeric matrix are called Functional Groups.
Functional Polymer: The matrix along with Functional Group is
called Functional Polymer or ion exchange resin.
Process of ion exchange
•Reversible: Ion exchange is a reversible process therefore, resin
can be converted from one ionic form to the other form, number
of times and reused.
•Regeneration: The process of converting resin to the desired
ionic form is called regeneration.
•Exhaustion: The resin is said to be exhausted when it cannot
exchange ions without effecting the desired quality of water.
Types Of Resins Used In Demineralization Plant
1.Strong acid cation resins (SAC):
The strong acid cation resin derived their exchange activity from sulphonic acid
group(-SO3H) phosphonic (H2PO3-).When operated on hydrogen cycle these
remove nearly all cations present in raw water. The strong acid cations can convert
neutral salts into corresponding acids.After exhaustion the resin can be regenerated
with HCl(4%)& NaCl(10%)
for demineralization and softening purpose,
repectively.
2.Weak acid cation resins(WAC):
The weak acid cation resins have –COOH group as exchange sites. These resins
have the capability of removing all cations associated with alkalinity to a much
greater degree than SAC resin. These do not function efficiently below pH 5.0, so
these cannot split weak salts effectively. The main asset of WAC resins is their high
regeneration efficiency which not only reduces the amount of acid required for
regeneration, but also minimizes the waste disposal problem. These are useful where
there is high degree of hardness and alkalinity. Frequently these are used in
conjunction with a strong acidic polishing resin.
3.Strong base anion resin (SBA):
•The Strong base anion resins derived their functionality from quaternary
ammonium exchange sites.These are capable of exchanging anions like Cl-,HCO3,Silica. Two type of SBA resins are commercially available and commonly referred
as Type-I & Type-II.
•Type-I site have three methyl groups while in Type-II resins an ethanol group
replaces one of the methyl groups. The Type-I resin has higher basicity, greater
chemical stability but somewhat less exchange capacity and low regeneration
efficiency. It is effective against organics & silica. The Type-I resins are favoured
for the high temperature applications.
•The Type-II resin is less stable but having slightly more capacity and
regeneration efficiency. In general, a Type–II SBA resin is recommended where
silica effluent quality is not as critical and also where a relatively high chloride
and/or sulphate content prevails in raw water.
•After exhaustion SBA resin can be regenerated with 4% NaOH.
4.Weak base anion resin (WBA):
•Weak anion resins derive their functionality from primary (RNH2),secondary(RNHR’)& tertiary amine (R3N)groups. The weak weak-base anion resins remove
free minerals acidity(FMA) such as HCl & H2SO4 but doesn’t remove weakly
ionized acids such silicic acid and bicarbonates.
• The main advantage of weak base exchangers is that they can be regenerated
with stoichiometric amount of regenerant, and are therefore, much more efficient.
These have a higher capacity for the removal of chlorides, sulphates.
• These are used in conjunction with SBA in demineralization system to reduce
regenerant cost and to attract organics thereby protecting the more susceptible
strongly basic
Classification of Ion Exchange Resins Based on Functionality
Resin
Type
functional
Group
Configuration
Example
(INDION)
Strong Acid
sulphonic
R-SO3H
225
Weak Acid
Carboxylic
R-CH2CHCH3
COOH
236
Strong
Base
TYPE-I
Strong
Base
TYPE-II
Weak
Quaternary
Ammonia
CH3
R-CH2N+CH3OHCH3
FFIP
Quaternary
Ammonia
CH3
R-CH2N+CH3OHCH2 CH2 OH
NIP
Tertiary
CH3
R-CH2N+HOH- 850
CH3
DM Plant
From filter
water pumps
ACF
For circuit rinse
WAC
SAC
WBA
SBA
MB
DM
water
storage
tank
Air
DEGASSER
To main plant for
boiler make up
DM Plant
Water quality at different stages of Demineralisation process:Feed water to DM plant
Turbidity - <2 NTU
ACF out
Residual chlorine - Nil
Turbidity - < 0.5 NTU
Cation Exchanger out
Na - <2 ppm
Degasser out
Dissolved CO2 - <5 ppm
DM Plant
Anion Exchanger out
Silica - < 200 ppb
Conductivity - < 10 ms/cm
pH
- 6.8 - 7.2
Mixed bed out
Silica - < 20 ppb
Conductivity - < 0.1 ms/cm
pH
- 6.8 - 7.2
Activated Carbon Filter
Service and Regeneration ( Back wash )
SI - Service Inlet
SO - Service Outlet
BWI - Backwash In
BWO - Backwash Out
RO - Rinse Out
SI
BO
Air
vent
BI
To Cation
Exchange
SO
RO
Drain
Cation Exchanger And Anion Exchanger
Service and Regeneration
Regeneration line to weak
exchanger
DF - Down Flow
Weak
Strong
Air
Vent
NF - Nozzle flushing
Air
Vent
NF
DF
SI
BI
BO
SI
BI
Acid/Alkali injection
RO
SO
Drain
BO RO
Drain
SO
Mixed bed
Service and Regeneration
Alkali injection
SI
Air
Vent
NF
Air
Drain
Acid injection
SO
Mixed Bed
Resin Separation
Anion exchange
Resin
Cation exchange
Resin
Ion-exchange Reactions
Cation Exchanger

During Service
NaCl
RH + CaCO3
MgSO4
Na2SiO3

RNa + HCl
R2Ca + H2CO3
R2Mg + H2SO4
RNa +H2SiO3
During Regenration
RNa
R2Ca + HCl
R2Mg
NaCl
RH + CaCl2
MgCl2
Ion-exchange Reactions
Anion Exchanger
 During Service
HCl
R’Cl
+
H2O
R’OH + H2CO3
R’2CO3
+
H2O
H2SO4
R’2SO4
+
H2O
H2SiO3
R’2SiO3
+
H2O
 During Regenration
R’Cl
R’2CO3
NaCl
+
NaOH
R’OH +
Na2CO3
R’2SO4
Na2SO4
R’2SiO3
Na2SiO3
Reverse Osmosis membrane
RO component and definition
 RO membrane is one of the most
important component in water
treatment system.
 RO is a process in which water is
purified using ion exclusion semipermeable membrane.
 Reverse Osmosis is the reversing
the Osmosis process
What is Osmosis
 It is the transfer of water from regions of low concentration to
region of high one to equilibrate between concentrations.
 The process stops when hydrostatic pressure on the high solute
side counter acts the osmotic pressure.
Reverse Osmosis
 The Osmosis process can be reversed by applying high pressure to
the high concentration (source water, reject) side through a
selective semi-permeable membrane.
 Membranes develop from natural pig bladder to synthetic
materials (polyamides-PA) membranes highly efficient at rejecting
contaminants.
 Membranes are made tough enough to withstand the greater
pressures necessary for efficient operation .
Reverse Osmosis vs. Osmosis
Pre-filters in RO systems
Prefilter
RO Pump
RO Membranes
 RO systems require a carbon pre-filter for the reduction of
chlorine (as mentioned before), which can damage an RO
membrane
 A sediment pre-filter is required to ensure that fine suspended
materials in the source water do not permanently clog the
membrane.
Reverse Osmosis – RO
 Effective for a variety of contaminants
 Relies on pressure to force water thru a
membrane
 Analogous to a filter
Electro dialysis
 Electro dialysis is an electrically driven process that use a voltage
potential to drive electrically charged ions through a semi-permeable
membrane reducing the total solved salts in the water sources.
 The process uses alternating semi-permeable cation and anion
transfer membranes in a direct current voltage potential field. The
source water flows between the cation and anion membranes. The
direct current voltage potential induces the cations to migrate
towards the anode through the cation membrane and the anions to
migrate towards the cathode through the anion membrane.
 The process cost is highest because the energy and the membrane
using are expensive.
DEMINERALISATION TECHNOLOGIES
ELECTRODIALYSIS
C
1
A
C
A
C
A
Na+
Na+
Na+
Cl-
Cl-
Cl-
2
3
4
5
6
7