22CYT13 & Chemistry for FT-Unit_I_WATER TECHNOLOGY.ppt

DEPARTMENT OF CHEMISTRY
22CYT13 & Chemistry for Food Technology
2022R
Unit-I-Water Technology
Prepared By
Krishnaveni K
Assistant Professor
Department of Chemistry
Kongu Engineering
College, Perundurai,
Erode
Course Outcome: Apply the suitable water softening
methods to avoid boiler troubles

Sources of Water
A) Surface Waters
Rain Water - Pure but contaminated with gases River Water -
High dissolved salts moderate organics Lake Water - Const.
composition but high organics Sea Water - High salinity,
pathogens, organics
B) Underground Waters
Spring/Well Water - Crystal clear but high dissolved salts and high
purity from organics

Classification of Impurities in water
1) Colour
2) Turbidity
3) Taste
4) Odour
5) Conductivity
1) Acidity (pH)
2) Gases (CO2-
O2, NH3)
3) Minerals
4) pH
5) Salinity
6) Alkalinity
7) Hardness
1)Microorganism
2)Water Bodies

MAJOR IMPURITIES OF WATER
Ionic and dissolved
Cationic
Calcium
Magnesium
Anionic
Bicarbonate
Carbonate
Hydroxide
Nonionic and undissolved
Turbidity, silt, mud, dirt and
other suspended matter
Gases
CO2
H2S
NH3
CH4
O2
Sodium
Potassium
Ammonium
Iron
Manganese
Sulfate
Chloride
Nitrate
Phosphate
Color, Plankton
Organic matter,
Colloidal silica,
Microorganisms,
Bacteria

Hardness of Water
•Hardness in Water is characteristic that prevents the ‘lathering of
soap’ thus water which does not produce lather with soap solution
readily, but forms a white curd is called hard water.
•Type of Hardness
–Temporary or Carbonate Hardness
–Permanent Hardness or non-carbonate Hardness.

Temporary Hardness
– Temporary Hardness is caused by the presence of dissolved bicarbonate of
calcium, magnesium and other heavy metals and the carbonate of iron. It is
mostly destroyed by more boiling of water, when bicarbonates are
decomposed yielding insoluble carbonates.
Ca(HCO 3)2
Calciumbicarbonate
Mg(HCO3)2
Heat CaCO3 + H2O + CO2
CalciumCarbonate
Mg(OH)2 + 2CO2
Magnesiumhydroxide
MagnesiumBicarbonate
Heat
– Calcium/Magnesium Carbonates thus formed being
almost insoluble, are deposited as a scale at the bottom
of vessel, while carbon dioxide escapes out.

Permanent Hardness
Non Carbonate Hardness is due to the presence of chlorides,
sulfates of calcium, Magnesium, iron and other heavy metals
2C17H35COONa + CaCl2
Sodium
(sodium soap)
2C17H35COONa + MgSO4
Sodium
stearate
stearate
(sodium soap)
Hardness
Hardness
(C17H35COO)2Ca +
2NaCl
Calcium stearate (Insoluble)
(C17H35COO)2Mg +
2Na2SO4
Magnesium stearate (Insoluble)

Units of Hardness
• Degrees French (oFr)
1o Fr = 1 part of CaCO3 eq per 105 parts ofwater

CaCO3 equivalent hardness
Calciumcarbonateequivalent =
Mass of hardness
producing substance
X Molecular weight
of CaCO3
Molecular weight of hardness producing
substances
Problem 1
Calculate the calcium carbonate equivalent hardness of a water sample containing 204mg of
CaSO4 per litre
Solution
:
Calciumcarbonateequivalenthardness=
204 100
136
= 150 mg of Ca CO 3
= 150 ppm

Calcium carbonate equivalence conversion during hardness
calculation
Hardness
producing
substance
Ca(HCO3)2
162
Mg(HCO3)2
146
CaSO4
136
CaCl 111
120
95
100
84
44
61
17
60

Problems
1. A water sample from an industry in Bombay had the following data
Mg(HCO3)2 = 16.8mg/L, MgCl2 = 19 mg/L, CaCO3 = 20 ppm, MgSO4 =24.0mg/L
and KOH = 1 ppm. Calculate the temporary, permanent and total hardness of the water sample.
Solution
Step 1 conversion in to Ca CO 3 equivalent
Constituent
present
Mg(HCO3)2
MgCl2 CaCO3
MgSO
quantity
16.8 mg/L
19.0 mg/L
20 ppm
24.0 mg/L
Conversion
factor
100/146
100/95
100/100
100/120
Hardness
16.8 *100/146 =
11.5ppm
19.0*100/95 = 20ppm
20.0*100/100 = 20 ppm
24.0*100/120 = 20 ppm
Calculation
Temp. Hardness = 31.5 ppm P. Hardness = 40 ppm
Tot. Hardness =71.5 ppm

Estimation of Hardness of Water by EDTA Method
• The hardness of water can be estimated by methods such as gravimetric
analysis, EDTA titration, atomic absorption, etc.,
• In the above methods, EDTA titration is the most inexpensive and simple way of
determining the hardness.
• hardness is usually determined by titrating it with a standard solution of
ethylenediamminetetraacetic acid, EDTA.
• The EDTA is a complexing, or chelating agent used to capture the metal ions.
This causes the water to become softened, but the metal ions are not removed
from the water.
• This method includes a series of titrations to determine the total, permanent,
temporary, Ca, Mg hardness of the given water sample.

Burette solution - Unknown EDTA solution
Pipette solution - 20 ml of Standard Hard water
Condition - Room Temp.
Reagents to
be added - 5 ml of buffer solution
Indicator - 2 drops of EBT (Eriochrome Black-T)
End point - Colour change from wine red to steel blue
Let the volume of EDTA consumed be V1 ml.
V1 ml of EDTA consumes 20 ml of
std. hard water = 20 * 1 mg of CaCO3 eq. hardness
1ml of EDTA consumes = 20/V1 mg of CaCO3 eq. hardness
(since 1ml of standard hard water= 1ml of CaCO3)

(ii) Estimation of Total Hardness:
Calculation
Burette solution - Standardised EDTA solution
Pipette solution - 20 ml of Sample Hard water
Reagents to

(iii) Estimation of Permanent Hardness:
Burette solution - Standardised EDTA solution
Pipette solution - 20 ml of Boiled Hard water
Reagents to

Alkalinity in water analysis:
In water analysis it is often desirable to know the kinds and amounts of the various of alkalinity present in
water.
The major portion of alkalinity in natural water is caused by presence of bicarbonates.
CaCO3 + CO2+H2O→Ca(HCO3)2
Classification:
1. Bicarbonate alkalinity
2. Carbonate alkalinity
3. Hydroxide alkalinity

Experimental Determination:
Principle
OH- + H+ → H2O (phenolphthalein end point)
CO3
2- + H+ →HCO3
- (phenolphthalein end point)
HCO3- + H+ → H2O + CO2
The results are summarized in table from which the amount of OH-,CO3
2-, HCO3
- present in water sample
can be calculated
Alkalinity OH- (ppm) CO3
2- (ppm) HCO3
- (ppm)
P=0 0 0 M
P=1/2M 0 2P 0
P<1/2 M 0 2P (M-2P)
P>1/2 M (2P-M) 2(M-P) 0
P=M M 0 0

Short Procedure
Standardisation of acid
Burette solution - Unknown H2SO4
Pipette solution - 20 ml of standard sodium hydroxide
Indicator - 2 drops of phenolphthalein
End Point - colour change from pink to colourless

All the three ions cannot exists together. OH- and HCO3 cannot be present at the same time
together, because
OH- + HCO3
- → CO3
2- + H2O
Procedure :
Burette solution - standard H2SO4
Pipette solution - 20 ml of water sample
Indicator - 2 drops of phenolphthalein and 2 drops of methyl orange
End Point - pink to colourless (V1 ml) and yellow to reddish orange (V2 ml).

Calculation
Volume of acid used up to phenolphthalein end point = V1 ml
Normality of acid = N1
phenolphthalein alkalinity(P) in terms of calcium carbonate
equivalent =V1*N1/20*50*1000 mg/lit
Additional volume of acid used up to methyl orange end point = V2 ml
Normality of acid = N1
methyl orange alkalinity (M) in terms of CaCO3 Equation = (V1+V2) * N1/20 *50*1000 mg/lit
Then the calculation of OH-, CO2-
3, HCO3
- is made with the help of above table.

Industrial use:
(i) Textile industry: Hard water causes much of the soap (used in washing yarn, fabric etc.) to go as waste,
because hard water cannot produce good quality of lather. Moreover, precipitated of calcium and
magnesium soaps adhere to the fabrics. These fabrics, when dyed latter on, do not produce exact shades of
color. Iron and manganese salts-containing water may cause coloured spots on fabrics, thereby spoiling
their beauty.
(ii) Sugar industry: Water containing sulphates, nitrates, alkali carbonated, etc., if used in sugar refining,
causes difficulties in the crystallization of sugar. Moreover, the sugar so-produced may be deliquescent.
(iii) Dyeing industry: The dissolved calcium, magnesium and iron salts in hard water may react with costly
dyes, forming undesirable precipitated, which yields impure shades and give spots on the fabrics being
dyed.
(iv) Paper industry: Calcium and magnesium salts tend to react with chemicals and other materials
employed to provide a smooth and glossy (i.e., shining) finish to paper. Moreover, iron salts may even
affect the colour of the paper being produced.
(v) Laundry: Hard water, if used in laundry, causes much of the soap used in washing to go as waste. Iron
salts may even cause coloration of the clothes.
(vi) Concrete making: Water containing chlorides and sulphates, if used for concrete making, affects the
hydration of cement and the final strength of the hardened concrete.
(vii) Pharmaceutical industry: Hard water, if used for preparing pharmaceutical products (like drugs,
injections, ointments, etc.) may produce certain undesirable products in them.
Disadvantages of using hard water in Industries

One of the chief use of water is generation of steam
by boilers.
Essential requirements of Boiler Feed Water :- It should
be free from
- Turbidity, oil, dissolved salts
- Hardness & scale forming constituents
- Dissolved O2 & CO2
- Caustic alkali

If hard Water is directly fed into boiler there arise
many problems such as
- Sludge & Scale Formation
- Boiler corrosion
- Caustic Embrittlement
- Priming & Foaming

1.Sludge
Slimy loose precipitate called
sludge suspended in water
water
Boiler wall
Sludge is a soft, loose
and slimy precipitate
formed within the boiler.
It can be easily scrapped
off with a wire brush.
It is formed at
comparatively colder
portions of the boiler and
collects in areas of the
system, where the flow
rate is slow or at bends.

1. Scale
Hard adherent coating
on inner walls of boiler
water
Boiler
wall
Scales are hard substances which sticks very firmly to the inner surfaces of
the boiler wall.
Scales are difficult to remove even with the help of a hammer and chisel.
Examples: Ca SO 4, CaCO 3, Mg( OH) 2

Sludge Scale
1. Sludges are soft and non- adherent
deposits.
1. Scales are hard deposits which stick very
firmly to the inner surface of boiler.
2. Sludges can be removed easily. 2. Scales are very difficult to remove.
3. Sludges can transfer heat to some
extent and is less dangerous.
3. Scales are bad conductors of heat and are
more dangerous.
4. Sludges are formed by substances
like MgCl2 and CaCl2.
4. Scales are formed by substances like
CaSO4 and Mg(OH)2.

Reasons for formation of scale
1. Presence of Ca(HCO 3) 2 in low pressure boilers
Ca(HCO 3)2 CaCO3 + H2O + CO2
Calcium bicarbonate Calcium Carbonate (scale)
Low pressure boilers but in high pressure boilers it is
soluble by forming Ca(OH) 2
2. Presence of Ca SO 4 in high pressure boilers
ToC
15
230
320
Cold water
Super
heated
(scale)
Solubility of CaSO 4
3200 ppm
15 ppm
27 ppm soluble
water
Insoluble
3. Presence of Mg Cl 2 in high temperature boilers
Mg Cl2 + 2 H 2O
Magnesium chloride
Mg(OH)2
scale
+ 2HCl
Mg(OH)2 can also be generated by thermally decomposing Mg(HCO 3)2
4. Presence of SiO 2
It forms insoluble hard adherent
CaSiO3 and MgSiO 3 as scales

Disadvantages of scale formation
1. Fuel wastage – scales have low thermal conductivity
2. Degradation of boiler material and increases of risk of accident
3.Reduces the efficiency of the boiler and- deposit on the valves and condensers
4.The boiler may explode – if crack occurs in scale
Remedies: Removal of scale
1. Using scrapper, wire brush often
2. By thermal shock- heating and cooling suddenly with cold water
3. Using chemicals – 5- 10% HCl and by adding EDTA

II. Caustic embitterment
Excess sodium carbonate used up for removing hardness can so result in the formation
of NaOH in high pressure boilers.
NaOH has better mobility and can percolate into fine cracks p r e s e n t in boiler
walls.
Na2CO3 + H2O → 2 NaOH +
CO2
Na OH gets concentrated in the fine cracks present in the boiler walls.
A concentration cell corrosion is established between the conc. NaOH and dilute Na
OH solution in contact with boiler walls.
Concentrated NaOH region behaves as anode thus resulting in corrosion of boiler
leading to the formation of sodium ferroate.
Remedies: ( i) Use phosphate salts instead of sodium carbonate ( ii) use Na 2SO 4 or
agar-agar gel compounds to f ill the fine cracks.

III. Priming and foaming
Foaming
It is the production of continuous foam or hard bubblers in
boilers. Foaming is due to the presence of substance like oil in
boiling water.
Priming
It is the process in which some particles in water are carried along
with the steam. The resulting process is called as wet steam or carry
over. The process of formation of wet steam in boilers is called as
priming.
Causes of Priming,
1.Presence of dissolved salts
2.High velocity steam due to sudden boiling
3.Improper boiler design
Foaming
Priming
Normal bubble
Carry over bubble

IV. Boiler corrosion
Degradation or destruction of boiler materials ( Fe) due to the chemical or
electrochemical attack of dissolved gases or salts is called boiler corrosion
Boiler corrosion is of three types
1. Corrosion due to dissolved O 2 2. Corrosion due to
dissolved CO 2
3. Corrosion due to acids formed by dissolved salts
1. Corrosion due to dissolved oxygen ( DO)
2 Fe + 2H2O + O2 2Fe(OH)2
4 Fe(OH)2 + O2
Ferrous hydroxide
2[Fe2O3.2H2O]
Rust

RemovalofDissolvedOxygen (DO)
1. Bytheadditionof chemicals
The dissolved oxygen present in the boiler feed water can be removed by the addition of sodium
sulphite or hydrazine and the reactions can be written as below
2 Na2SO3 + O2 2 Na2SO4
Na2S + 2O2
N2H4 + O2
Na2SO4
N2 + 2H2O
Sodium sulphite DO Sodium sulphate
Hydrazine
Nitrogen
2. Bymechanical deaeration
I t comprises of a tall stainless tower with different layers capped
with baffles to facilitate multiple equilibration.
The entire chamber is vacuumized and also maintained at high
tempt using perforated heating plates on the walls.
Water feed
To vacuum
Steam jacket
Perforated plate
Deaerate d
water

2. Corrosion due to dissolved CO2
Presence of bicarbonate salts of either magnesium or calcium also causes the release of CO 2 inside the
boiler apart from the dissolved CO 2
Mg( HCO 3 )2
CO 2
CO 2 + H
2O
corrosion)
Removal
Mg CO 3 + H2O +
H 2 CO3 (causes slow
1. I t can be removed by the addition of ammonia
2 NH 4OH + CO 2 (NH 4 ) 2CO 3 + H 2 O
3 . Corrosion due to dissolved salts
MgCl2 + 2 H2O Mg(OH)2 + 2HCl
Fe + 2 HCl FeCl2+ H2
FeCl2 + 2 H2O Fe(OH)2+2HCl

Methods of softening
 Internal treatment process
 External treatment method
Softening of water
“Process of removing hardness”
“Hardness is due to the presence of calcium, magnesium ions”

41
Internal treatment process
Colloidal conditioning
Phosphate conditioning
Carbonate conditioning
Calgon conditioning
Sodium aluminate conditioning
Electrical conditioning
Radioactive conditioning
 Softening of water can be done at the boiler itself
 Addition of chemical to the boiler water to
 Precipitate scale forming impurities which can be removed
 Convert the impurities into soluble compounds

42
Carbonate conditioning
Scale Loose sludge
Calgon conditioning

43
External treatment process
 Removal of Ca, Mg and other salts which would form insoluble metallic soaps
externally
 Before feed into boilers, its softened
Lime soda process
Zeolite process
Ion-Exchange (or) Demineralisation

Ion-Exchange (or) Demineralisation (or) Deionization process
Ion exchange resins are insoluble, cross linked, long
chain organic polymers with a microporous
structure, and the functional groups attached to the
chain is responsible for the “ion-exchange”
properties.
Cation exchange
Resin
Resin after
treatment

In general the resins containing acidic functional groups (-COOH, -SO3H etc) are capable of exchanging
their H+ ions with other cations, which comes in their contact; whereas those containing basic functional
groups ( -NH2, =NH as hydrochlorides) are capable of exchanging their anions with other ions, which
comes in their contact.
Based on the above fact the resins are classified into two types
1. Cation exchange resin (RH+) –
Strongly acidic (SO3
-H+) and weakly acidic (COO-H+) cation exchange resins
2. Anion Exchange resin (ROH-) –
Strongly basic (R4N+OH-) and weakly basic (RNH2
+OH-) anion exchangeresins
Continued… next slide
Resins..

Structure of Cation and Anoin resins
R = CH3
Cation exchange resin Anion exchange resin

Ion exchange purifier (or) softener
Cation exchange Resin Anion exchange Resin
Gravel
bed
Hard
water
Injector
Injector
Alkaline solution for
regeneration of resin
Wastages to
sink
Wastages to
sink
Acid
solution for
regeneratio
n of resin
pump
Soft water

-
Reactions occurring at Cation exchange resin
Reactions occurring at Anion exchange resin
At the end of the process
Process or Ion-exchange mechanism involved in water softening

Advantages
1.The process can be used to soften highly acidic or alkaline waters
2.It produces water of very low hardness of 1-2ppm. So the treated waters by this
method can be used in high pressure boilers
Disadvantages
1.The setup is costly and it uses costly chemicals
2.The water should not be turbid and the turbidity level should not be more than
10ppm
Regeneration of Cation exchange resin
Regeneration of Anion exchange resin
Regeneration of ion exchange resins

50
Treatment of water for municipal water supply
Requirements of drinking water
 Clear, odourless
 Good taste
 Suspended particle < 10 ppm
 pH = 7-8
 Dissolved salts < 500 ppm
 Fluoride < 1.5 ppm
 Free from dissolved gases like H2S, ….
 Should not have heavy metals
 Free from pathogens
 Removal of suspended particles
 Disinfection of pathogens
Major steps involved in treatments

51
 Screening
 Aeration
 Settling in big tank to remove suspended particles
 Sedimentation occurs by adding coagulants (alum, etc). Precipitates
contains aluminium, ferrous, ferric hydroxides…
Steps involved
Removal of suspended particles
Chemical coagulants
 Alum

 Sodium aluminate
 Ferrous sulphate

 Finally filter through sand / gravity filters

54
Disinfection of pathogens
Sterilization
“Process of removing, killing, deactivating microorganisms” such as fungi,
bacteria, viruses, spores, unicellular eukaryotic organisms such as
Plasmodium, etc.) and other biological agents..

55
Sterilization by physical methods

56
Sterilization by chemical methods
Commonly used Disinfectants
- Chlorine (Cl2)
- Chlorine dioxide (ClO2)
- Hypo chlorite (OCl-)
- Ozone (O3)
- Halogens: bromine (Br2), iodine (I)
- Bromine chloride (BrCl)
- Metals: copper (Cu2+), silver (Ag+)
- Potassium Permanganate (KMnO4)
- Alcohols
- Soaps and detergents
- Hydrogen peroxide
- Several acids and bases

Roles of Disinfectants
 Minimization of DBP (Disinfection By-Products) formation (strong oxidants, including
potassium permanganate and ozone, may be used to control DBP)
 Oxidation of iron and manganese
 Prevention of regrowth in the distribution system and maintenance of biological stability
 Removal of taste and odours through chemical oxidation
 Improvement of coagulation and
filtration efficiency
 Prevention of algal growth in
sedimentation basins and filters
 Removal of colour

58
By adding bleaching powder
Some examples of chemical sterilization methods
By adding Chloramine

59
By doing Ozonisation
Advantages
 Sterilisation, bleaching, decolourisation, de-odourisation done at same time
 Ozone does not impact unpleasant taste, odour, no change in pH
 Dosage, 2-3 ppm; time 10-15 mins
Disadvantages
 Expensive

60
Breakpoint chlorination
 Process involving in adding chlorine or chlorine compounds such as sodium hypochlorite
to water which kills bacteria, viruses and other microbes in water
 Addition of chlorine to a water decreases the initial chlorine level. However, the organic
matters (containing ammonia or nitrogen) present in the water starts decomposition which
produces an increased combined chlorine content which is used to kill pathogens.
 In a stage where no further chlorination , and the oxidation of chloramines / other
impurities starts which results in fall in combined chlorine content.
 After complete oxidation, residual
chlorine starts increasing at a certain
point which is termed as “Break point
chlorination”

 De-chlorination
Advantages
 Completely oxidises organic compounds, ammonia,…..
 Removes colour
 Destroy bacteria 100% completely
 Removes odour, bad taste
 Prevents growth of weeds

22CYT13 & Chemistry for FT-Unit_I_WATER TECHNOLOGY.ppt

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