Environmental Engineering -I
- BY PROF S S JAHAGIRDAR
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
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. Decreases CO2 content and raises
5. Removes Iron and Manganese.
6. Due to agitation bacteria may get
7. Can be used for mixing chemicals
HOW DOES AERATION WORK?
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.
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
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
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.
efficiency of the aeration process
depends almost entirely on the amount of
surface contact between the air and
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
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
= 4Fe(OH)3 - +
+ O2 =
oxidation products, ferric
hydroxide and manganese dioxide,
After aeration, they are removed by
clarification or filtration.
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
1. CASCADE AERATOR
of free fall aerator
Can be constructed of concrete or
Height is 1 to 3 m.
50 to 60% CO2 reduction
2. INCLINED APRON AERATOR WITH RIFFLE
falls along inclined
Breaking up of water due to aprons
Agitation increases contact of air
3. SLAT TRAY AERATOR
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
Ventilator discharges air and gases
4. GRAVEL BED AERATOR
is sprayed at the top and it
trickles down the bed of coke or
Thickness of bed is 1 to 1.5 m
trays are kept filled with coke or
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.
1. Air diffusion is type of _______ system.
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.
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.