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)
LAYOUT
SCREENING
AERATION
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2. Screening
i. Water derived from surface sources contain floating and
suspended matter.
ii. Removes impurities like wood, leaves, aquatic plants,
papers, polythene, sand silt etc.
iii. Serve as protective device for the remaining plant rather
than as a treatment process.
iv. Two Types:
i. Coarse Screens
ii. Fine Screens
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3. Coarse Screens or Bar Screens
i. Intercept larger floating matter.
ii. Form of Bar Grill
iii. 25 mm in size and spaced at 75 – 100 mm
c/c.
iv. Inclined – easy cleaning
v. The strained water enters the screen box,
leaving behind the sediment
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4. Fine Screens
i. Used at Surface water intakes.
ii. Automatic Cleaning devices to prevent
clogging.
iii. Drum type having hole of 6 mm diameter.
iv. Automatic Strainers
v. Work continuously eliminating solids from
the liquid flowing and disposing these
solids continuously.
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5. Aeration
i. Water and air in close contact
ii. Can be achieved either by
i. Exposing drops or thin layers of water to the
air
ii. By introducing small air bubbles at the
bottom and letting them rise through the
water.
iii. Efficiency depends on:
i. Contact time
ii. Amount of surface contact between air and
water
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6. Aeration
Objectives
i. Removes taste and odors caused by gases
due to organic decomposition.
ii. Increases dissolved oxygen content.
iii. Removes Hydrogen Sulphide and hence
Odour.
iv. Decreases carbon dioxide thereby reducing
corrosiveness and increasing pH.
v. Converts Iron and Manganese from their
soluble states to insoluble state and
therefore can be precipitated.
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7. Aeration
Objectives
vi. Some quantity of bacteria's are killed
during agitation.
vii. Used for mixing chemicals with water. E.g.
prior to the process of coagulation.
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8. Types of Aerators
Gravity Aerators (Cascades):
i. Simplest form
ii. Water is allowed to fall by gravity
iii. Series of steps such that a large area of
water is exposed to atmosphere, sometimes
aided by turbulence.
iv. Open air
v. Carbon dioxide reduction 50 – 60 %
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9. Types of Aerators
Inclined Apron aerator with riffle plates
i. Water falls along an Inclined plane/apron.
ii. Breaking up of sheet of water causing
agitation and consequent aeration.
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10. Types of Aerators
Slate Tray Aerators:
i. Most common.
ii. Consists of series of trays equipped with
slats or perforated or wire meshed bottoms.
iii. Water enters the top and is evenly
distributed over the topmost tray.
iv. Slates are staggered falls from one slate to
the center of the other.
v. Some cases Air is supplied from the
bottom.
vi. Water is collected from the collector pan
(Bottom)
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11. Types of Aerators
Packed Tower:
i. Water is pumped into the top of the tower
packed with inert material.
ii. Centrifugal blowers are used to introduce
air countercurrent through the bottom of
the tower.
iii. Beds of Coke, Limestone or anthracite is
more efficient in Carbon dioxide removal.
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12. Types of Aerators
Fountain (Spray) Aerators:
i. divide the water flow into fine streams and
small droplets.
ii. Come in intimate contact with air due to
trajectory.
iii. Water is sprinkled in fine jets through
nozzles.
iv. Carbon dioxide removal 70 – 90%
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13. Types of Aerators
Injection (Diffused) Aerators:
i. Perforated pipe network is installed at the
bottom of the tank.
ii. Compressed air is blown through these
pipes.
iii. Air bubbles move upwards causing
Aeration.
iv. Detention period = 15 mins.
v. Depth = 3- 5 m
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14. Types of Aerators
Mechanical Aerators:
i. Submerged or partially submerged
impellers, which are centrally mounted in
the aeration tank.
ii. Surface aerators agitate the wastewater
vigorously, entraining air in the wastewater
and causing a rapid change of the air-water
interface to facilitate solution of the air.
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15. Aeration Effects
Effective Against:
i. Dissolved gases such as radon, carbon dioxide
ii. Some taste and Odour problems such as methane, and hydrogen sulfide
iii. Volatile organic compounds, like MTBE or industrial solvents
iv. Aeration can be used for the precipitation and removal of iron and manganese
v. Aeration raises the pH of water.
Not Effective Against:
i. Other heavy metals
ii. Pathogenic (disease‐causing) organisms like bacteria and viruses
iii. Turbidity and suspended materials
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16. 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.
ASST. PROF. PRACHI DESSAI 22