3 Water
3 Water
3 Water
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“ALTHOUGH WATER IS NATURE’S
MOST WONDERFUL, ABUNDANT &
USEFUL COMPOUND, YET IS ALSO
THE MOST MISUSED ONE”
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Importance of Water
• The most valuable gift to all living beings including plants and
animals
generation
etc
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Importance of Water
• Water being a universal solvent (all dissolving), seldom occurs
water purification
rupees
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Various Sources of Water
Sources
River water
Lake water
Sea water
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• Rain Water: Purest form of water. Since it is obtained
suspended particles
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Impurities in Water
Characteristics
Organic/Inorganic
Color impurities
Microorganisms
Taste
Odour
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Physical Impurity - Color
• Color in water is due to dissolved substances &
substances present as fine colloids. e.g.
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Physical Impurity - Odor
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Chemical Impurity – Organic/Inorganic
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Chemical Impurity – Organic/Inorganic
Mineral matter:
• Origins from rocks & industrial effluents
• These includes Mineral, acids, Ca2+, Mg2+,
Na+, K+, Fe2+, CO32- etc.
• Industrially Hardness & alkalinity are
important.
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Chemical Impurity – Gases
• Water contains dissolved gases ex.
i. CO2: It is not assumed as an impurity, but water used
in industries some times needed to get rid of it.
CO2 is present due to atmospheric & biological
oxidation of organic matter.
CH4 + O2 → CO2 + H2O
ii. O2: All natural water has dissolved oxygen. It is very
imp for aquatic lives but it is a great nuisance in
industrial purposes.
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Chemical Impurity – Gases
The test for oxygen is carried out for determining
Dissolved Oxygen [DO] of polluted water &
industrial effluents & constitutes a means of
controlling water pollution.
iii. NH3: it is acquired from decomposition (aerobic &
anaerobic) of Nitrogenous organic matter (in polluted
& sewage water) and urea.
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Biological Impurities
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Biological Impurities
Micro-organism: Algae, fungi,& bacteria form slime
& there by causing fouling & corrosion. This slime
clogs the spray nozzle & screens of the circulating
pipes of AC & other industrial plants. In order to
control these, chemical treatment like chlorination is
done.
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HARDNESS OF WATER
• Hardness of water is that characteristic which prevents
the lathering of soap. This is due to presence of certain
salts of Ca, Mg & other heavy metals dissolved in
water. This water when treated with soap (Na or K salts
of higher fatty acids like, oleic palmitic, or stearic) forms
a white scum or ppt of insoluble soaps of Ca & Mg
• Other metal ions like Fe2+, Mn2+, and Al3+ also react
with soap in a similar manner, thus contributing to water
hardness Water 22
HARDNESS OF WATER
2C17H35COONa + CaCl2 → (C17H35COO)2Ca ↓ + 2NaCl
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Temporary/Carbonate/Alkaline Hardness
• Temporary hardness is caused by the less soluble carbonates
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Concentration of different impurities
(found in underground v/s river or lake water)
Concentration range in Concentration range in
Impurity
underground water river/lake water
Max. limit of TDS i.e. total dissolved solids in drinking water is 500 ppm
Sep 9, 2012 Water 28
Expressing water hardness (units)
Soft 0 – 60
drinking
making
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Disadvantages of Hard Water (Domestic)
i. Washing/Cleaning:
clothing, giving stains on clothes making them look less than clean
ii. Bathing:
• Shower lines get clogged due to continuous deposition of salts from hard
water
iii. Cooking:
• Foods like pulses, beans, vegetables, etc. do not cook properly in hard
water
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Disadvantages of Hard Water (Domestic)
iv. Drinking:
• Long term use of hard water could result in harmful effects on the
• Has bad effect on metabolic system. Calcium oxalate stones may develop
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Disadvantages of Hard Water (Industrial)
i. Textile industry:
• Hard water used for washing yarn, fabric, etc. in the textile
• Dyeing of such fabric does not produce the desired color shade
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Disadvantages of Hard Water (Industrial)
iv. Paper industry: Reaction with chemicals to provide smooth & glossy
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Effect of Hard/Impure Water (In Boilers)
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Effect of Hard/Impure Water (In Boilers)
i. Sludge and Scales:
saturation point
₢ Sludges get collected in the areas (where the flow rate is slow)
other salts that have greater solubility in hot water than in cold
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water
Effect of Hard/Impure Water (In Boilers) - Sludge
• Effect of sludge formation (disadvantages of sludge):
efficiency is compromised
of a wire brush
• Prevention of Sludge:
• Formation of scales:
† Scales are the hard deposits of the salts that firmly stick to
† In high pressure boilers the CaCO3 further reacts with water under
precipitates from the hot water in the boiler, and gets deposited on
the inner walls of the boiler. This is the main cause of scale
‡ Scales are low conductors of heat and obstruct or restrict the heat
‡ Scales thus cause overheating of the boiler and hence fuel wastage
b) Decrease of efficiency:
‡ Scales get deposited in the valves and condensers of the boiler, choke these
‡ Scales being bad conductors of heat, result in the overheating of the boiler tubes
‡ The boiler thus becomes unsafe to bear the pressure of steam, especially in high
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pressure boilers
Effect of Hard/Impure Water (In Boilers) - Scales
which causes the hot water to come in contact with the boiler wall
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Effect of Hard/Impure Water (In Boilers) - Scales
heating, and the sudden contact of the hot water with the boiler wall
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Effect of Hard/Impure Water (In Boilers) - Scales
• Removal of scales:
heating the boiler and then sudden cooling with cold water
to dissolve them ex. CaCO3 scales can be dissolved using 10% HCl
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Difference between sludges and scales
Sludges Scales
Loose, slimy ppt which remain Hard, adhering deposits on the walls
floating in water or get collected & bottom of the boiler are called
at bottom of boiler are called scales.
sludges.
Formation is due to salts with Formation is due to salts with higher
lower solubility in cold water, eg, solubility in cold water, eg, CaSO4
MgCO3
Risk of explosion does not Explosion may take place.
persist.
Methods for removal: carping by Method for removal: Internal
wire brush, scalpel. treatment by dilute acids,
complexation.
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Other effects of impure water in the boiler
2NaOH + Fe Na2FeO2 + H2
(sodium ferroate)
This causes embrittlement of the boiler wall at stressed parts like
bends, joints, etc
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Other effects of impure water in the boiler
carbonate
1. Dissolved O2
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Priming
consumption.
3. It should be cool
4. The total dissolved solids (TDS) should be less than 500 ppm
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Drinking Water Purification
ȸ Drinking water should pass the following specifications:
organisms
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Drinking Water Purification
Drinking water purification consists of:
number of holes where the bigger sized floating material is trapped and
removed
2. Sedimentation:
about 2 – 6 hours
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Drinking Water Purification
A. Removal of suspended impurities:
2. Sedimentation:
o Using coagulants, fine clay and colloidal particles are made to form a
o The coagulants used are alum, sodium aluminate and ferrous sulfate
o The positively charged ions such as Al3+ and Fe2+ from the coagulants,
neutralize the negative charge on the colloidal particles, which then come
closer and unite to form bigger flocks that settle down under gravity
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Drinking Water Purification
A. Removal of suspended impurities:
2. Sedimentation:
o The coagulants in solution form, are thoroughly mixed with the water before
sedimentation
o Alum is used when the water has some alkalinity. If the alkalinity of water is
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Drinking Water Purification
A. Removal of suspended impurities:
2. Sedimentation:
7.0
fine sand and other proper sized granular material. During this process most
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Drinking Water Purification
B. Removal of micro-organisms:
from the water and making it safe, is called as disinfection, and the
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Drinking Water Purification
B. Removal of micro-organisms:
1. Boiling
3. Chlorination
5. Ozonization
6. UV treatment
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Drinking Water Purification
B. Removal of micro-organisms: (chlorination method of disinfection)
o The chlorinator consists of a high tower fitted with a number of baffle plates
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Drinking Water Purification
B. Removal of micro-organisms: (chlorination method of disinfection)
powerful germicide
The HOCl interacts with the enzymes in the cells of the micro-organisms
Cl2 + H2O HOCl + HCl
and thus stop their metabolic processes
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Drinking Water Purification
B. Removal of micro-organisms: (chlorination method of disinfection)
Thus, Cl2 is most effective at water pH less than 6.5 where the HOCl exists
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Drinking Water Purification
B. Removal of micro-organisms: (chlorination method of disinfection)
c. The quantity of free Cl2 in treated water should not exceed 0.1 – 0.2 ppm
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Drinking Water Purification
B. Removal of micro-organisms: (Ozonization method of disinfection)
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Drinking Water Purification
B. Removal of micro-organisms: (Ozonization method of disinfection)
Ozonization process:
Ozone is injected into water, and the two are allowed to come into
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Drinking Water Purification
B. Removal of micro-organisms: (Ozonization method of disinfection)
Advantages of ozonization:
oxygen
(Decomposition)
O3 O2 + [ O ]
(Ozone) (Nascent oxygen)
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Drinking Water Purification
B. Removal of micro-organisms: (Ozonization method of disinfection)
Disadvantages of ozonization:
expensive. Therefore, the method cannot be used for the large scale
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Drinking Water Purification
B. Removal of micro-organisms: (UV method of disinfection)
reproduction
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Drinking Water Purification
B. Removal of micro-organisms: (UV method of disinfection)
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Drinking Water Purification
B. Removal of micro-organisms: (UV method of disinfection)
ᴥ Limitations of UV treatment:
i. Water with high levels of suspended solids (which shield the microorganisms),
turbidity, color, or soluble organic matter, can react with the incident UV
ii. Water with such impurities should be first treated via a reverse osmosis
radiations
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Drinking Water Purification
B. Removal of micro-organisms: (UV method of disinfection)
ᴥ Applications of UV treatment:
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