Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.

1. WATER SUPPLY ENGINEERING
(ENVIRONMENT ENGINEERING I)
SOFTENING OF WATER

2. Softening of
Water
Water softening is the removal of
calcium, magnesium, and certain other
metal cations in hard water.
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3. What is hard and soft water?
Water which readily gives a lather with 'soapy' soap (not detergents) is described as SOFT water.
'Hard water' means the water does not readily give a good lather with soap
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4. HARDNESS OF WATER
It is a property of water, which prevents the lathering of the soap.
Hardness is of two types.
Temporary hardness: It is caused due to the presence of carbonates and sulphates of calcium and
magnesium. It is removed by boiling.
Permanent hardness: It is caused due to the presence of chlorides and nitrates of calcium and magnesium.
It is removed by zeolite method.
Hardness of water is determined by EDTA method
Permanent Hardness: is caused sulfate and calcium.
Permissible hardness: 75 – 115 mg/l (Drinking Purpose)
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5. HARDNESS REMOVAL
Generally a hardness of 100 to 150 mg/liter is desirable. Excess of hardness leads to the following
effects.
1. Large soap consumption in washing and bathing
2. Fabrics when washed become rough and strained with precipitates.
3. Not fit for industrial use like textiles, paper making, dye and ice cream manufactures.
4. Precipitates clog the pores on the skin and makes the skin rough
5. Precipitates can choke pipe lines and values
6. Forms scales in the boilers tubes and reduces their efficiency and cause in encrustations
7. Not palatable
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6. METHODS OF REMOVAL OF
HARDNESS
1. Boiling
2. Freezing
3. Lime addition
4. Lime soda process
5. Excess Lime treatment
6. Caustic soda process
7. Zeolite process
8. Demineralization or exchange process.
Methods 1,2 and 3 are suitable for removal of temporary hardness and 4 to 8 for both temperory
and permanent hardness. The temporary hardness is removed as follows.
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7. BOILING & ADDITION OF LIME
(TH)
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8. LIME AND SODAASH (PH)
Lime soda ash –: In this method, the lime and is sodium carbonate or soda as have used to remove
permanent hardness from water. The chemical reactions involved in this process are as follows.
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9. LIME SODAASH METHOD
Advantages:
◦ Economical
◦ Less coagulant
◦ Kills pathogen upon prolonged exposure
◦ Reduces mineral content
Disadvantages
◦ High sludge quantity
◦ Skilled workmanship
◦ Recarbonation is necessary to avoid
encrustation
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10. BASE EXCHANGE PROCESS &
ZEOLITE PROCESS
Principle
Zeolites are compounds (silicates of aluminum and sodium) which replace sodium Ions with
calcium and magnesium Ions when hardwater is passes through a bed of zeolites. The zeolite can
be regenerated by passing a concentrated solution of sodium chloride through the bed. The
chemical reactions involved are
Cation exchange
◦ 𝑁𝑎2𝑍 + 𝐶𝑎(𝐻𝐶𝑂3)2 → 𝑁𝑎2(𝐻𝐶𝑂3)2 + 𝐶𝑎𝑍
◦ 𝑁𝑎2𝑍 + 𝑀𝑔(𝐻𝐶𝑂3)2 → 𝑁𝑎2(𝐻𝐶𝑂3)2 + 𝑀𝑔 𝑍
Regeneration
◦ 𝐶𝑎𝑍 + 2NaCl → 𝑁𝑎2𝑍 +𝐶𝑎Cl2
◦ 𝑀𝑔𝑍 + 2NaCl → 𝑁𝑎2𝑍 +MgCl2
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11. BASE EXCHANGE PROCESS &
ZEOLITE PROCESS
Zeolites
Advantages
1. In this process, the sludge is not formed hence problem of sludge disposal does not arise
2. It can be operated easily and no skilled supervision required
3. The hardness of water reduces to zero and hence used for boiler and texile industries
4. The process is economical where salt is cheaply available
5. The load on Zeolite can be reduced by combining it with lime or aeration process
Disadvantages
1. The Zeolite process cannot be used for turbed or acidic water
2. The Zeolite process is unsuitable for water containing Iron and Manganese
3. The Zeolite should be operated carefully to avoid injury or damage to the equipmen
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12. DEMINERALISATION
Both cations and anions are removed by resins
similar to zeolites in two columns by iron
exchange method.
Resins may be regenerated with sulfuric acid
and sodium carbonate.
This process is used in industries to get
distilled water
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13. Recommended Readings
i. Mark J. Hammer; Water and Waste Water Technology; Prentice Hall of India.
ii. S. K. Garg; Water Supply Engineering; Khanna Publ.
iii. B. C. Punmia, A. K. Jain; Water Supply Engineering; Laxmi Publication.
iv. G. S. Birdie; Water Supply Engineering and Sanitary Engineering; Dhanpat Rai.
v. R. C. Rangwala; Water Supply Engineering, Charotar Publ. House.
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