Environmental Engineering-I (Water Supply Engg.) - TE (CIVIL) Course material by PROF S S JAHAGIRDAR, NKOCET, SOLAPUR.

1. Environmental Engineering -I
L-9
AERATION
UNIT-II
- BY PROF S S JAHAGIRDAR

2. INTRODUCTION
Aeration is used to remove tastes
and odours, and
to remove minerals such as iron
and manganese from water, and
to remove carbon dioxide from the
water.


3. OBJECTIVES OF AERATION
1. Removes taste and odours caused
due to organic gases.
2. Increases dissolved oxygen content
3. Removes Hydrogen Sulphide and
odour due to it.

4. 4. Decreases CO2 content and raises
pH.
5. Removes Iron and Manganese.
6. Due to agitation bacteria may get
killed.
7. Can be used for mixing chemicals

5. HOW DOES AERATION WORK?
Aeration
is the intimate exposure of
water and air.
It is a way of thoroughly mixing the
air and water so that various
reactions can occur between the
components of the air and the
components of the water.

6. Scrubbing action
Oxidation

7.  Aeration
removes or modifies the
constituents of water using two
methods - scrubbing action and
oxidation. Scrubbing action is caused
by turbulence which results when the
water and air mix together. The
scrubbing action physically removes
gases from solution in the water,
allowing them to escape into the
surrounding air.


8. Scrubbing
action will remove tastes
and odors from water if the problem
is caused by relatively volatile
gases and organic compounds.
Oxidation is the other process
through which aeration purifies
water.

9. When air is mixed with water, some
impurities in the water, such as iron
and manganese, become oxidized.
 Once oxidized, these chemicals fall
out of solution and become
suspended in the water.
The suspended material can then
be removed later in the treatment
process through filtration.


10. EFFICIENCY
 The
efficiency of the aeration process
depends almost entirely on the amount of
surface contact between the air and
water.
 This contact is controlled primarily by the
size of the water droplet or air bubble.
 The goal of an aerator is to increase the
surface area of water coming in contact
with air so that more air can react with the
water.

11. IRON AND MANGANESE REMOVAL
Iron and manganese in well waters occur as soluble ferrous
and manganous bicarbonates. In the aeration process, the
water is saturated with oxygen to promote the following
reactions:
4Fe(HCO3)2 +
ferrous bicarb
onate
O2
oxygen
2H2O
= 4Fe(OH)3 - +
8CO2
water
+
ferric
hydroxide
carbon
dioxide
2Mn(HCO3)2
+ O2 =
2MnO2
manganese
bicarbonate
oxyg
en
manganese
dioxide
+
4CO2 carbon
dioxide
+
2H2O
water

12. The
oxidation products, ferric
hydroxide and manganese dioxide,
are insoluble.
 After aeration, they are removed by
clarification or filtration.

13. TYPES OF AERATOR
1. Free fall or gravity aerator
i. Cascade aerator
ii. Inclined apron aerator
iii. Slat tray aerator
iv. Gravel bed aerator
2. Spray aerators
3. Air diffusers
4. Mechanical aerators

15. 1. CASCADE AERATOR
Simplest
of free fall aerator
Can be constructed of concrete or
metal
Height is 1 to 3 m.
50 to 60% CO2 reduction

21. 2. INCLINED APRON AERATOR WITH RIFFLE
PLATES
Water
falls along inclined
plane/apron.
Breaking up of water due to aprons
cause agitation
Agitation increases contact of air
and water

23. 3. SLAT TRAY AERATOR
 Consists
of closely stacked super
imposed wood slat-trays
 Water is sprayed evenly on top tray.
 Water trickles from one tray to the other.
 Air is supplied at the bottom with the
help of blower (Air flow is in upward
direction).
 Ventilator discharges air and gases

25. 4. GRAVEL BED AERATOR
Water
is sprayed at the top and it
trickles down the bed of coke or
anthracite.
Thickness of bed is 1 to 1.5 m

27. TRICKLING BEDS
3-4
trays are kept filled with coke or
stone
Thickness of bed is – 0.5 to 0.6 m
Distance between trays is 0.5m
Water is sprayed from distribution
pipe at the top.

34. OBJECTIVE QUESTIONS
1. Air diffusion is type of _______ system.
(chlorination/aeration/flocculation/sedimentation).
2. Iron and Manganese are removed by
____________ action in aeration.
3. ___________ aerator is commonly used in
water treatment plants.
4. Diffused and mechanical aerator are mostly
used in _____________ treatment.

35. THEORY QUESTIONS
Q1. Write note on objectives of
aeration. Also enlist types of
aerators. (Dec 2011, 5 marks)
Q2. Enlist different types of aerators
and discuss with neat sketch any
one in detail.