Advance water treatment

AERATOR
 It is a mechanical process of bringing water in
intimate contact with air, so as to absorb oxygen and
to remove carbon dioxide gas.
 It may also help in killing bacteria to a certain
extent.
 It may also helps in removing H2S gas, and iron and
manganese to a certain extent, from the treated
water.
2

It serves,
To increase dissolved oxygen content.
To remove tastes and odours.
To remove hydrogen sulphide.
To decrease carbon-di-oxide.
To convert iron and manganese from soluble to
insoluble states.
To kill bacterias to some extent. 3

METHODS OF AERATION
The methods aeration of water can be carried out
in one of the following ways:
By using spray nozzels
By permitting water to trickle over cascades
By air diffusion
By using trickling bed 4

1. By using spray nozzels:
 In this method, water is sprinkled in air or
atmosphere through special nozzles which breaks
the water into droplets, thus permitting the escape
of dissolved gases.
 CO2 gas is removed( upto 90% or so) in this
method.
5

2. By permitting water to trickle over cascades:
It is a waterfall and a simple cascade consists of a
series of three or four steps. The steps may be of
concrete or metal.
The water is made to fall through a certain height
(1 to3m) over a series of steps (3 to 10) with a fall of
about 0.15 to 0.3 m in each step.
The structure so formed is know as a freefall
aerator. The simplest type of a freefall aerator is
know as a cascade aerator.
6

3. By air diffusion:
 In this method, compressed air is bubbled through
the water, so as to thoroughly mix it with water.
 Perforated pipes are installed at the bottom of the
settling tanks, and the compressed air is blown
through them.
 The air bubbles while coming up from the bottom of
tank and aeration of water is thus achieved.
 The depth of aeration tanks is generally kept as
about 2.5 to 3m . they work on the principle of
continuous flow with minimum detention period of
15 minutes.
8

 The quantity of air consumed per 1000 litres of
water varies from 0.3m3
to 0.6 m3
9

4. By using trickling bed:
 In this method, the water is allowed to trickle down the
beds of coke, supported over perforated trays, and
arranged vertically in series.
 Three beds are used, the depth of each being about 0.6m.
 The water is applied from the top through perforated
distribution pipes and allowed to trickle down, up to the
bottom bed.
10

 During this downward motion, the water gets
mixed up with air, and aeration takes place.
 The size of the coke varies from 50mm to 75mm.
 This method is found to be less effective than that
of “spray nozzles”. But it gives better results than
what can be obtained by “cascades”
11

WATER SOFTENING
It is the process of reduction or removal of hardness
from water.
Advantage of softening
 Reduction of soap consumption
 Lowered cost in maintaining plumbing fixtures
 Improved taste of food preparation.
 To avoid corrosion and incrustation of pipes
12

TYPES OF HARDNESS:
Following are the two types of hardness:
 Temporary hardness or carbonate hardness
 Permanent hardness or non-carbonate
hardness
13

TEMPORARY HARDNESS OR
CARBONATE HARDNESS
 The temporary hardness is caused by the
bicarbonate and carbonate of calcium and
magnesium are present in water.
 It can be removed either
 By Boling
 By addition of lime
14

By Boling:
Calcium carbonate soluble in water,
usually exist in water as calcium
bicarbonate, because it easily
dissolved in natural water containing CO2.
Water is boiled, the CO2 gas will
get out, leading to the precipitation
of CaCO3, which can be sedimented out in settling tank.
The reaction can be represented as
Ca(HCO3)2 + Heat CaCO3 + CO2 + H2O
Cal.bicarbonate Cal.Carbonate
15

PERMANENT HARDNESS:
 The permanent or non-carbonate hardness which is caused
by the sulphates, chlorides and nitrates of calcium and
magnesium.
 The permanent hardness is more permanent and difficult to
remove.
 The methods of removing permanent hardness are
 Lime-Soda process
 Base-Exchange process or Zeolite process
 Demineralisation process
16

LIME-SODA PROCESS
 In this process, lime and soda ash are used to
remove permanent hardness from water.
 It react with calcium and magnesium salts and
form insoluble precipitates of CaCO3 and Mg(OH)2
 The precipitates can be removed by sedimentation.
17

ADVANTAGES OF LIME-SODA
PROCESS:
 The pH value of treated water increases which
reducing the corrosion of the distribution system.
 Minimises coagulant dosage
 Removes iron and manganese to some extent
 Reduces total mineral content of water
 Removes pathogenic bacteria by some amount
 The process is economical
18

DISADVANTAGE:
 Disposal of the sludge formed is very difficult.
 Requires skilled supervision.
 Requires recarbonation.
 Cannot produce zero hardness
19

ZEOLITE OR BASE-EXCHAGE
PROCESS :
 The zeolite or base-exchage process or cation-
exchange process is also one of the removal of
hardness.
 Zeolite are the natural salts or clays which are
hydrated silicates of sodium and aluminium
 The zeolite or Resins are exchanging their cations,
and during softening operation.
 The sodium ions of the zeolite get replaced by the Ca
& Mg ions present in hard waters. 20

 It may be gravity or pressure filters.
 Pressure filter type zeolite softeners being more
common.
 It consists of closed steel
Cyclinder.
 Tk of bed – 0.75 to 2m
 Rate of filtration-
100-300lit/sq.m/min
 It will results in a water
of zero hardness, not
Suitable for public supplies.
21

ADVANTAGES OF ZEOLITE
PROCESS:
Water of zero hardness, and useful for sp. Uses in
textile indutries, boliers etc..,
The plant is compact automatically and easy to operate.
No sludge is formed
The RMO(running, maintenance and operation) cost is
quite less.
Removes ferrous iron and manganese from H2O
No problem of incrustation of pipes of the distribution
system.
No difficult to treating H2O
22

Advance water treatment

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