water and its treatment.pdf

• Introduction
• Hardness of Water
• Determination of Hardness
• Water Softening Techniques
• Waste water and its treatments
• Specifications for drinking water
Contents

❖ Water is nature’s most wonderful, abundant and useful compound.
❖ It is the only substance that occurs naturally as a solid, liquid and gas.
❖ solvent of great importance
❖ Water is not only essential for the lives of animals and plants, but also
occupies a unique position in industries.
❖ Water is used in for the production of electricity
❖ Water is also used in chemical plants, paper industries, pharmaceutical
industries, textile industries, steel industries, food industries as well as in
atomic reactors
❖ Useful in irrigation for agricultural purposes
❖ widely used in domestic uses such as drinking, bathing, washings, sanitary
etc.
❖ Although water is nature’s most wonderful and abundant compound but
only less than 1% of the world’s water resources is available for ready use.
Introduction

• Only 3% (69% resides in glaciers, 30%
underground, and less than 1% is
located in lakes, rivers and swamps) of
water on the surface is fresh; the
remaining 97% resides in the ocean.
• Looked at another way, only 1% of the
water on the Earth’s surface is usable
by humans.

Sources of Water
Sources of
Water
Rain Water
Surface
Water
River
Water
Lake
Water
Sea
Water
Ground Water

Impurities in Water
Impurities in
Water
Dissolved
impurities
Inorganic
salts
Organic
constituents
Gases
Suspended
impurities
Inorganic
impurities
Organic
impurities
Colloidal
impurities
Microorganism
Cations: Ca2+, Mg2+, Fe2+, Al3+, Mn2+, Na+, K+,
Zn2+, Cu2+ etc.
Anions: HCO3
-, Cl-, SO4
2-, NO3
-, CO3
2-, F- etc.
Aldrin, benzene, carbon tetrachloride, chlordane,
tetrachloroethane, trichloroethane, chloroform,
lindane, methoxychlor etc.
SOx, NOx, CO2, H2S etc
Sand, Clay etc
Oil globules, vegetable and animal matter
Finely divided silica and clay, organic waste
products
Algae, Fungi, bacteria etc

1. Hard Water
2. Soft Water
Types of Water
Hard Water
• Does not produce lather with soap solution
• Contain dissolved salts of Ca and Mg
• Large quantity of soap is required for washing
• Due to presence of dissolved salts, boiling point of hard water is elevated, so more fuel is consumed
Soft Water
• Forms lather very easily with soap solution
• Doesn’t contain dissolved salts of Ca and Mg
• Soap is not wasted
• Less fuel is required
Two types of water- based on dissolved impurities

Merits
Soft Water Hard Water
✓ CLEAN HOME with NATURAL PRODUCTS : Chemical free
soaps, laundering agents and other natural household cleaners are
more effective when mixed with soft water
✓ IMPACT on HAIR and SKIN : Using soft water , hair and skin
feels softer, cleaner and smoother, as opposed to brittle and dry
✓ SILVERWARE and GLASSWARE : Using soft water while
washing we get a clean, shinny, streak free.
✓ LONG - LASTING APPLIANCES : Soft water preserves the
life of water using appliances. Cheaper heating in cold winters
using soft water can be done
✓ BETTER PLUMBING : Soft water is used to have a good flow
of water in pipes.
✓ SAVING MONEY : Soft water easily lathers up when mixed
with soap and shampoo reduces the usage and costs.
✓ No Boiler Troubles
✓ BETTER TASTE : The taste of hard water is better than
soft water
✓ PLANTS : Plants are sensitive to sodium levels hence
using soft water can affect their growth. Distilled, neutral
water is best for plants.
✓ There are no serious adverse health issues associated
with drinking hard water.
✓ STRENGTHEN BONE AND TEETH : It act as a
dietary supplement of both Ca and Mg
✓ Coating of limescale inside pipes, stops poisonous salts
dissolving into water.
✓ CONSTIPATION and DIGESTION : Ca and Mg
reduces the constipation. Even Ca combines with the
excess bile and fats, and then it is eliminated from our
body

✓ LESS FORMATION of LATHER : While washing clothes with
hard water, the soap forms white precipitates instead of
producing lather
✓ SPOTS and STAINS : Scum stains the clothes and also the
colour of clothes gets faded . White watermarks are left on the
utensils, bath tiles, glass and bath fittings gets stained.
✓ IMPACT on HAIR and SKIN : It makes the hair dry and rough
and skin dry and itchy
✓ REDUCES the LIFE of APPLIANCES : The appliances wear
out earlier and efficiency is decreased .
✓ CORROSION of PIPES . It not only corrode the pipe but also
clog it . It can lead to galvanic corrosion in an electrolytes
✓ PLANT RISKS : Hard water can cause blockages in the plant's
root system
✓ Boiler Troubles
Demerits Soft Water
Hard Water
✓ HEALTH ISSUES : Its harmful for ( diabetics of with high BP )
who are sensitive to high salinity , or sodium levels
✓ PLANTS : Plants are sensitive to sodium levels hence using soft
water can stunt their growth of plants
✓ AQUARIUMS : Soft water is susceptible to pH fluctuations
while fish require strict pH levels to remain healthy in the
environment .
✓ Soft water can easily lead to poisoning if it is transferred through
lead pipes or kept in lead containers.
✓ Soft water is tasteless which is not pleasant in mouth.
✓ Soft water does not help in strengthening our bones and teeth
since it doesn't have calcium .

➢ Hardness in water is mainly derived from soil and host rock.
➢ Rainwater as it falls upon the earth is capable of dissolving some amount of solids found in many
natural waters.
➢ The ability of the water increase to dissolve the solids in soil when the CO2 is released by
microbial action.
➢ The concentration of CO2 in soil water increases and that exist in equilibrium with carbonic acid
(H2CO3). Due to formation of H2CO3 (a weak acid), pH lowered and solubility of the elements
increases.
CaCO3 + H2O + CO2 → Ca(HCO3)2
➢ Groundwater is hard where the top soil cover is thick and availability of limestone, a carbonate
rock that dissolves more in acidic condition.
➢ Groundwater is soft where the top soil cover is thin and limestone formation is sparse.
Origin of hardness in water

• Hardness is that characteristics of water by which it can prevent the formation of
lather / foam with soap solution.”
• also defined as the soap consuming capacity of water.
• Presence of certain salts of Ca, Mg and other heavy metal ions like Al3+, Fe3+ and
Mn2+
• Typical reactions of soap with water(CaCl2 and MgCl2) does not produce lather but
forms insoluble white scum or precipitate
2C17H35COONa + CaCl2 → (C17H35COO)2Ca↓ + 2NaCl
2C17H35COONa + MgCl2 → (C17H35COO)2Mg↓ + 2NaCl
Soap
Sodium stearate
Dissolved
salts
White ppts
(SCUM)
Benefits…… providing dietary Ca and Mg and reducing the solubility of potentially
toxic metal ions such as lead, Copper etc.
Hardness of Water

Types of Hardness
Ca(HCO3)2 CaCO3 + H2O + CO2
Mg(HCO3)2 Mg(OH)2 + 2CO2
1. Temporary hardness
1. Temporary Hardness 2. Permanent Hardness
This method is not practical for large scale softening.
Temporary hardness can also be removed by the addition of calculated amount of lime(clark’s method).
• Presence of dissolved bicarbonates of calcium and magnesium and other heavy metals
• Removed simply by boiling the water
• On boiling, soluble bicarbonates are decomposed into insoluble carbonates and it can easily
removed by filtration
Ca(HCO3)2, Mg(HCO3)2, CaCO3, MgCO3, Mg(OH)2, Ca(OH)2
Carbonate hardness or alkaline hardness

❖ Presence of dissolved chlorides and sulphates of calcium and magnesium, iron
and other heavy metals
❖ Not removed by boiling
❖ Required other methods for removing
❖ Non-Carbonate hardness or non-alkaline hardness
2. Permanent hardness
Types of Hardness
CaCl2, MgCl2, CaSO4, MgSO4, Mg(NO3)2

Sea, brackish and other waters contain appreciable amounts of Na+ interfere with
normal behaviour of soap because of common ion effect.
Sodium is not a hardness causing cation and so this action which it exhibits when
present in high concentration is called as pseudo-hardness
Pseudo-Hardness
Types of Water Parts per million (ppm)
Soft 0-50
Moderately soft 50-100
Slightly soft 100-150
Moderately hard 150-200
Hard 200-300
Very hard Over 300
Classification of water
according to hardness

❖ Hardness of water is conveniently expressed in terms of equivalent
amount of CaCO3
.
❖ Molecular mass is 100
❖ Most insoluble salt that can be precipitated in water treatment
❖ Most common substance in hardness
CaCO3 equivalent=
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠
𝑝𝑟𝑜𝑑𝑢𝑐𝑖𝑛𝑔 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒
𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠
x Molecular weight of CaCO3
CaCO3 equivalent=
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠
𝐸𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠
x Equivalent weight of CaCO3
Degree of Hardness

Units of Hardness
°Cl °Fr ppm mg/L
It is the parts of calcium carbonate equivalent hardness per a particular number of
parts of water depending upon the unit used
1 °Cl = 1 part CaCO3
equivalent hardness per
70,000 parts of water
degree Clark
1 °Fr = 1 part CaCO3
105 parts of water
degree French
1 ppm = 1 part CaCO3
106 parts of water
1 mg/L = 1 mg of CaCO3
103 parts of water
1 mg/L = 1 ppm = 0.10Fr = 0.070Cl

Conversion factors for harness causing impurities
Atomic mass
Ca= 40
Mg= 24
Cl = 35.5
C= 12
Na= 23
K= 39
S= 32
O= 16
N= 14

• Alkalinity is the name given to the quantitative capacity of water to neutralize
an acid.
• It can also be referred as conc of all the ions which are capable of neutralizing
H+ ion.
• Due to OH−, CO3
−2, HCO3
− ions
Caustic alkalinity OH- + H+ → H2O
Carbonate alkalinity CO3
-2 + 2H+ → CO2 + H2O
Bicarbonate alkalinity HCO3
- + H+ → CO2 + H2O
• Source may be Inorganic, organic and dissolved gases.
Alkalinity

Identification of ions present and Calculation of volume of sulphuric acid
consumed
OH- + H+ H2O
CO3
2- + H+ HCO3
-
HCO3
- + H+ CO2 + H2O
Neutralization of Ions
M= OH- + CO3
2- + HCO3
-
P= OH- + ½CO3
2-
M-P= ½CO3
2- + HCO3
-
Case 1 P=0
Indicates the absence of OH- & CO3
2-
Hence only HCO3
- is present
Volume of H2SO4 to neutralise OH- = 0 ml
Volume of H2SO4 to neutralise CO3
2- = 0 ml
Volume of H2SO4 to neutralise HCO3
2- = M ml
P= OH- & ½ CO3
2-
M= OH- & ½ CO3
2- & HCO3
-
M-P= ½ CO3
2- & HCO3
-
P M
OH-
CO3
2-
HCO3
-
Free mineral acids
10.2
8.3
4.5
pH
Phenolphthelein (P)
Methyl Orange (M)

Case 2 P=M
Indicates the absence of CO3
2- & HCO3
-
Hence only OH- is present
Volume of H2SO4 to neutralise OH- = M ml
2- = 0 ml
2- = 0 ml
Case 3 P = ½M
Indicates the absence of CO3
2- & HCO3
-
Hence only CO3
2- is present
2- = M ml
2- = 0 ml

Case 4 P > ½M
Indicates the absence of HCO3
-
Hence OH- & CO3
2- are present
2- = 2(M-P) ml
Volume of H2SO4 to neutralise OH- = M-2(M-P) ml
2- = 0 ml
Case 5 P < ½M
Indicates the absence of OH-
Hence CO3
2- & HCO3
- are present
2- = M=2P ml
2- = (M-2P) ml

Relation of Phenolphthalein & Methyl Orange readings with the
possibility of alkalinity producing ions
S. NO. Result of Titration OH- ion CO3
2- ion HCO3
- ion
1 P = 0 Nil Nil M
2 P = M P or M Nil Nil
3 P = ½ M
(V1=V2)
Nil 2P Nil
4 P > ½ M
(V1>V2)
2P-M 2(M-P) Nil
5 P < ½ M
(V1<V2)
Nil 2P M-2P

Methods of Softening Hard Water
Water Softening
methos
External
Treatment
Removal of
hardness
Zeolite
Process
Ion
exchange
Lime-Soda
Process
Removal of Salts
(Desalination)
Electrodialysis
Reverse
Osmosis
Internal
Treatment
Carbonate
Conditioning
Phosphate
Conditioning
Calgon
Conditioning
❖ The process by which hard water is converted into soft water is known as Water softening.
❖ Hardness causing salts can be removed by two ways:

❖ Permutit or zeolite are complex silicates of Al and Na and has formula
Na2O.Al2O3.xSiO2.yH2O, where x = 2-10 and y = 2-6
❖ These silicates are porous and hold Na ions loosely hence, these are called
hydrated sodium alumina silicate, capable of exchanging its Na+ with hardness-
producing metal ions in water
❖ Zeolites find application in softening of water for domestic and industrial purposes.
(i) Natural Zeolites
Natrolite: Na2O.Al2O3.SiO2.H2O
Thomsonite: Na2O.Al2O3.3SiO2.2H2O
Analcine: Na2O.Al2O3.4SiO2.3H2O
(ii) Synthetic Zeolites
Na2O.Al2O3.xSiO2.yH2O
x = 5-13 and y = 3-4
Artifical zeolites are called
permutit and have high
exchange capacity
Zeolite Process or Permutit
❖ Zeolites are commercially known as permutes and are of two types:

Zeolite Process Diagram
❖ Principle: In this process, the hard water is
allowed to percolate through a bed of zeolite
which retains the Ca2+ and Mg2+ ions from
hard water by exchanging with Na ions
thereby the out flowing water contains
sodium salts.

• Hard water is allowed to pass through a bed of zeolite at specified rate
• The Ca2+ and Mg2+ salts react with it forming insoluble Ca and Mg permutit (CaZe)
and (MgZe)
• The outgoing water contains sodium salts but free from hardness causing metal
ions
Ca(HCO3)2 + Na2Ze → CaZe + 2NaHCO3
Mg(HCO3)2 + Na2Ze → MgZe + 2NaHCO3
CaCl2 + Na2Ze → CaZe + 2NaCl
MgCl2 + Na2Ze → MgZe + 2NaCl
CaSO4 + Na2Ze → CaZe + Na2SO4
MgSO4 + Na2Ze → MgZe + Na2SO4
Temp. Hardness
Perm. Hardness

• When most of the portion of sodium ions are in the zeolite has been replaced
by Ca and Mg ions
• It is to be regenerated by first washing it with water and then treating it
with brine solution (10% NaCl solution)
Regeneration Process

Limitations of Zeolite Process
• The presence of turbid water reduces the efficiency of zeolite, as it will clogs the pores
of the zeolite bed
• In presence of coloured ions such as Mn2+ and Fe3+, they should be removed first
otherwise it will difficult to regenerate the zeolite bed
• Water containing mineral acids, will destroy the zeolite bed hence water should be
neutralized first.
Advantages
• Zeolite can remove hardness up to 10 ppm
• The equipment used is compact and occupies less space
• No impurities are precipitated hence no sludge is formed….it is clean process
• The running, maintenance and operation cost is less
• It removes iron and manganese from the water
• It requires less skill for maintenance as well as operation.

• Treated water contains excess of sodium salts. The total solid content, due to the
chloride and sulphate ions of sodium, is not decreased or removed and remained
in the softened water.
• It leaves all the acidic ions such bicarbonates, chlorides, sulphates as such in the
softened water. For example, in boilers NaHCO3 dissociates forming NaOH and
CO2. Such water can not be used in high pressure boilers
• The treated water contains more dissolved salts than treated by lime-soda
process.
Disadvantages

Ion-exchange resins are insoluble, cross-linked, long chain organic polymers with a
microporous structure and the functional groups attached to the chains are
responsible for the ion-exchanging properties.
Ion-exchange resins may be classified as:
(a) Cation exchange resins (RH+)
They are mainly styrene-divinyl benzene co-polymers, which on sulphonation or
carboxylation becomes capable to exchange their hydrogen ions with the cations in the
water.
Therefore they are known as cation exchangers.
Ion-exchange Process
Principle: The cations and anions that are present in hard water are permitted to flow
through the ion exchanger resin so that the hydrogen and hydroxide ions of the resin
can exchange with them producing soft water.

(b) Anion exchange resins (R-OH)
They are styrene-divinyl benzene co-polymes, which contain amino or quaternary
ammonium groups
These after treatment with dil. NaOH solution become capable to exchange their OH-
anions with the anions present in hard water
Therefore they are known as anion exchangers.

The hard water is first passed through cation exchange column, where all the cations
like Ca2+ and Mg2+ etc are removed from it and equivalent amount of H+ ions are
released from this column to water
Reactions
The acidic water is then passed through another column containing anion exchanger,
where equivalent amount of OH- ions are released
Reactions
Water thus produced is free from all ions and are called deionized or demineralized
water
2R-H + CaSO4 → R2Ca + H2SO4
2R-H + CaCl2 → R2Ca + 2HCl
2 R-H + MgSO4 → R2Mg + H2SO4
2R-H + MgCl2 → R2Mg + 2HCl
2R-OH + SO4
2- → R2SO4 + OH-
R-OH + Cl- → R-Cl + OH-

Regeneration Process
When capacities of cation and anion exchangers to exchange H+ and OH- are lost,
they are called exhausted resins
The exhausted cation exchanger is then regenerated by passing a dilute solution of
acid
Reactions
The exhausted anion exchanger is regenerated by passing a dilute solution of alkali
Reactions
R2Ca + 2HCl → 2R-H + CaCl2
R2Mg + 2HCl → 2R-H + MgCl2
R2SO4 + 2NaOH → 2R-OH + Na2SO4
R-Cl + NaOH → R-OH + NaCl

• The Process can be used to soften highly acidic or alkaline water
• The residual hardness in about 2ppm
• All ions are removed thereby problems like caustic embrittlement/ boiler
corrosion are reduced when treated water is used for boiler feed purpose.
Disadvantages
• Cost is high
• Turbid water decreases the efficiency of the process
• Monitoring of the softened water at intervals is required
• Organic and microbial impurities cannot be removed.
Advantage and Disadvantage of Ion-exchange Process
Advantages

• Chemically converts all the soluble hardness causing impurities into the insoluble
precipitates, filtered off
• A suspension of milk of lime Ca(OH)2 and required amount of soda Na2CO3 added in
requisite amount
• This process is now obsolete but was very useful for the treatment of large volume of hard
water.
Principle: Calculated quantity of lime
& soda are added to hard water to
convert soluble hardness causing
impurities into insoluble one which are
easily removed by settling or filtration.
Lime-Soda Process
Lime Soda
Process
Cold lime
soda process
Intermittent
type
Continuous
type
Hot lime
soda process
Intermittent
type
Continuous
type

• Soda removes all the soluble calcium permanent hardness, which is originally
present as well as which is introduced during the removal of Mg, Fe, HCl,
H2SO4 etc by lime method.

Intermittent/Batch type Cold Lime Soda process
Intermittent/Batch type Hot Lime Soda process is similar to the cold lime batch
process except that heating coils are installed and coagulants not required.

Cold Lime-Soda Process (continuous type)
• Done at room temperature
• Precipitates formed are very fine
• Do not settle down easily and cause difficulty
in filtration
• Coagulants (NaAlO2 and Al2(SO4)3) added,
they hydrolyze to precipitates which entraps
the fine particles
• slow process
• Softened water has residual hardness 60 ppm
• low softening capacity

Hot Lime-Soda Process (continuous type)
• High softening capacity
• Done at elevated temperature (94 - 100 ℃)
• rapid process
• Filtration is easy as the viscosity of water
becomes low
• Coagulants not needed
• Dissolved gases removed
• Softened water has residual hardness 15-30ppm

Advantages of Lime-Soda process
• Very economical
• Iron and manganese are also removed
• Soft water obtained by this method is alkaline and so less corrosion
• The alkaline water reduce the amount of pathogens.

Disadvantages of Lime-Soda process
• Disposal of large amount of sludge is a problem.
• Skilled supervision is required.
• Appreciable concentrations of soluble Na salts, not suitable for high pressure
boilers
• Soft water is of 15 ppm hardness, not ideal for boilers.

Water containing high concentration of dissolved solids with a peculiar salty taste
is called Brackish water.
Depending upon the amount of dissolved solids, water is classified as:
(a) Fresh water (< 1000ppm of dissolved solids)
(b) Brackish water( 1000 to 30000 ppm of dissolved solids)
(c) Sea water( 30000-50000 ppm of dissolved solids)
(d) Brine water (>50000 ppm of dissolved solids)
The process of eliminating dissolved solids from water is known as desalination.
• The demand of fresh water can be solved by desalination process of sea water
• Its an expensive process
• In spite of high price, desalination has been used at various places
Desalination of Brackish Water

Electrodialysis Process
Based on the fact that the ions present in saline water migrate towards their respective
electrodes through ion-selective membranes under the influence of applied electric field.
cation-
selective
membranes
anion-
selective
membranes

• The unit consist of electrodes (cathode & anode) and thin and rigid ion-selective
membrane, which is permeable to either cations or anions
• The anode is placed near the anion-selective membrane while the cathode is placed
near the cation-selective membrane
• Under the influence of an applied emf across the electrodes the cation move
towards the anode through the cation-selective membrane and anions move toward
the anode through anion-selective membrane.
• Hence increase the concentration of cations and anions in the left and right
compartments
• Desalinated water is drawn out from the central compartment.

Advantages
• The process is economical as per the capital cost and operation expenses
• The unit is compact
Disadvantages
Organic, microbial impurities and hardness
cannot be removed

Reverse Osmosis Process
When two solutions of unequal concentrations are separated by a semipermeable
membrane, flow of solvent take place from dilute to concentrated sides due to
osmosis
If a hydrostatic pressure in excess
of osmotic pressure is applied on
the concentrated side, the solvent
flow reverse i.e. moves from
concentrated to diluted side
through semipermeable membrane,
known as Reverse Osmosis (RO) or
Superfilteration or Hyperfilteration

Simple Schematic Diagram of working of Reverse Osmosis System
Factors affecting the quantity and quality of RO water
1. Pressure – 60psi
2. Temperature – 24.4 ℃ ideal. 4.44 ℃ - RO water fall to half. Max temp- 32.2 ℃
3. TDS
4. Membrane (Thin Film Composites : TFC)

In this process, semipermeable membrane, base on thin films of cellulose acetate,
polymethyl acrylate, polyamide polymers or thin film composites (TFC) etc are
used
A pressure of 15-40 kg/cm2 is applied for separating the pure water from the
saline water
The amount of pressure required depends on the salt concentration of the feed
water.
• The more concentrated the feed water, the more pressure is required to
overcome the osmotic pressure

Advantages
• Simple, compact and reliable process
• Removes all types of impurities such as ionic, non-ionic, colloidal, organic
molecules such as THM (Chloroform), DBCP, Lindane, PCE (perchloroethylene),
Carbon tetrachloride, chlorine etc.
• Requires 30% less energy as compared to other desalination processes
• The life of semipermeable membrane is quite high, reduces the maintenance cost
• Compact and operating expenses are low
• Colloidal SiO2 impurities can be removed by RO which even cannot removed by
demineralization process

Disadvantages
• Usually not applicable for highly concentrated solutions
• RO membranes are susceptible to fouling so feed steams requires pre-treatments
• Does not remove volatile organic chemicals (VOC), chlorine, chloramines. Some
RO have multi-stage filtration methods (in addition to the RO membrane) such as
activated carbon, which can remove chlorine and pesticides.
• Wastage of water (5:1)
• RO feed steams must be compatible with membrane and other materials of device.
Manoj Vora

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