Water Treatment-Domestic

TREATMENT OF
WATER

GUIDED BY:- SHUBHAM BAPHANA
Er. Ravi Parmar sir CE (3RD YEAR)
Er. Sugandh singh sir 0862CE101115

The available raw water must be
treated and purified before they can
be supplied to the public for domestic
use or any industrial use. The extent of
treatment of water depends upon
following two-

1.Characteristics and quality of
available water.
2.Quality requirements for the
intended use.

Parameters Desirable-Undesirable If no alternative source
available, limit
extended upto
PHYSICAL
Turbidity (NTU unit) < 10 25
Colour (Hazen scale) < 10 50
Taste and Odour Un-objectionable Un-objectionable
CHEMICAL
pH 7.0-8.5 6.5-9.2
Total Dissolved Solids
500-1500 3000
mg/l
Total Hardness mg/l
200-300 600
(as CaCO3)
Chlorides mg/l (as Cl) 200-250 1000
Sulphates mg/l (as
150-200 400
SO4)
Fluorides mg/l (as F ) 0.6-1.2 1.5
Nitrates mg/l (as NO3) 45 45

Unit treatment Function (removal)
Aeration, chemicals use Colour, Odour, Taste
Screening Floating matter
Chemical methods Iron, Manganese, etc.
Softening Hardness
Sedimentation Suspended matter
Suspended matter, a part of
Coagulation
colloidal matter and bacteria
Remaining colloidal dissolved
Filtration
matter, bacteria
Pathogenic bacteria, Organic
Disinfection
matter and Reducing substances

Source Treatment required
1. Ground water and spring water No treatment or Chlorination
fairly free from contamination
2. Ground water with chemicals, Aeration, coagulation (if
minerals and gases necessary), filtration and
disinfection
3. Lakes, surface water reservoirs Disinfection
with less amount of pollution
4. Other surface waters such as Complete treatment
rivers, canals and impounded
reservoirs with a considerable
amount of pollution

AERATION:-

•Aeration removes odor due to volatile gases and due
to algae and related organisms.

•Removes CO2 and reduce corrosion and remove
methane and other inflammable gases.

•Increases dissolved oxygen content in water.

Aeration
Gravity aerators
Fountain aerators
Diffused aerators
Mechanical aerators

FOUNTAIN AERATOR MECHANICAL AERATOR

DIFFUSED AERATOR GRAVITY AERATOR

Settling:-
In this Solid particle are separated out from the water.
• Clarified floating particle at the top of the sedimentation tank.
• Concentrated sludge leaving the bottom of the sedimentation
tank.

Purpose of settling:-
• To remove Coarse dispersed phase.
• To remove coagulated and flocculated impurities.
• To settle the Sludge.

Principle of settling:-
• Suspended solid present in water having specific gravity greater
than that of water tend to settle down by gravity.
• Basing in which the flow is retarded is called settling tank.
• Theoretical average time for which the water is detained in the
settling tank is called Detention Time.

Types of settling:-
1. Type 1 Discrete particle settling:-

• In discrete settling individual particles settle independently.
• It occurs when there is a relatively low solids concentration.

2. Type 2 Flocculent particle settling:-
• In flocculant settling, individual particles stick together into clumps
called flocs.
• This occurs when there is a greater solids concentration and
chemical or biological reactions alter particle surfaces to enhance
attachment.

3. Type 3 Compression:-
Compression settling occurs when particles settle by compressing
the mass below

4. Type 4 Zone settling:-

Type of settling tank:-

1. Intermittent or Quiescent Type tank:- Those which store water for a
certain period and keep it in complete rest.
2. Continuous Flow type tank:- The flow velocity is reduced and the water
is not bought to complete rest as is done in above one.

Long Rectangular Settling basin:-

• They are hydraulically more stable and flow control for large volume is
easier with this configuration.
• Length is 2 to 4 times of widht with bottom to be made slope.

This long rectangular settling basin is divided in four zones:-

Inlet zone: Region in which the flow is uniformly distributed over the cross
section.
Settling zone: Settling occurs.
Outlet zone: Clarified effluent is collected and discharge through outlet
weir.
Sludge zone: For collection of sludge below settling zone.

Circular Basin:-
• Circular settling basins have the same functional zones as the long
rectangular basin, but the flow regime is different. When the flow enters at
the centre and is baffled to flow radially towards the perimeter, the
horizontal velocity of the water is continuously decreasing as the distance
from the center increases.
• Sludge removal mechanisms in circular tanks are simpler and require
less maintenance.

Design Details:-
1. Detention period: for plain sedimentation: 3 to 4 h, and for
coagulated sedimentation: 2 to 2.5 h.
2. Velocity of flow: Not greater than 30 cm/min (horizontal
flow).
3. Tank dimensions: L:B = 3 to 5:1. Generally L= 30 m (common)
maximum 100 m. Breadth= 6 m to 10 m. Circular: Diameter
not greater than 60 m. generally 20 to 40 m.
4. Depth 2.5 to 5.0 m (3 m).
5. Surface Overflow Rate: For plain sedimentation 12000 to
18000 L/d/m2 tank area; for thoroughly flocculated water
24000 to 30000 L/d/m2 tank area.
6. Slopes: Rectangular 1% towards inlet and circular 8%.

Coagulation and flocculation:-

• Colloidal particles are difficult to separate from water because they do
not settle by gravity and are so small that they pass through the pores of
filtration media.
• To be removed, the individual colloids must aggregate and grow in size.
•The aggregation of colloidal particles can be considered as involving two
separate and distinct steps:
a. Particle transport to effect interparticle collision.
b. Particle destabilization to permit attachment when contact occurs.
Flocculation:-

It is a common practice to provide an initial rapid (or) flash mix for the
dispersal of the coagulant or other chemicals into the water. Slow mixing is
then done, during which the growth of the floc takes place.

Rapid or Flash mixing is the process by which a coagulant is rapidly and
uniformly dispersed through the mass of water. Generally, the detention
period is 30 to 60 seconds and the head loss is 20 to 60 cms of water. Here
colloids are destabilised and the nucleus for the floc is formed.

Slow mixing brings the contacts between the finely divided destabilised
matter formed during rapid mixing.

-:Filltration:-
To remove or to reduce the remaining impurities still further, the water
is filtered through the beds of fine granular material, such as
sand, etc. The process of passing the water through the beds of such
granular materials is known as Filtration.
-:Filter material:-
1. Sand:-Sand, either fine or coarse, is generally used as filter media
The size of sand is measured and expressed by the term called
effective size.
2. Gravel:- The layer of sand may be supported on gravel, which
permits the filtered water to move freely to the under drains.
3. Other materials:- Instead of using sand, sometimes anthrafilt is
used as filter media. Anthrafilt is made from anthracite. It is
cheaper and has been able to give high rate of filtration.

TYPES OF FILTERS

1. Slow Sand filter:- They consist of fine sand, supported by gravel.
They capture particles near the surface of the bed and are
usually cleaned by scraping away the top layer of sand that
contains the particles.

2. Rapid sand Filter:- They consist of larger sand grains supported
by gravel and capture particles throughout the bed. They are
cleaned by backwashing water through the bed to 'lift out' the
particles.

3. Multemedia Filter:- They consist of two or more layers of different
granular materials, with different densities. Usually, anthracite
coal, sand, and gravel are used. Because of the differences in
densities, the layers stay neatly separated, even after backwashing.

Difference Between SSF and RSF:-

Slow sand filter Rapid sand filter
Base Material varies from 3 to 65 mm varies from 3 to 40 mm
in size and 30 to 75 cm in size and its depth is
in depth slightly more, i.e. about
60 to 90 cm.
Filter sand the effective size In RSF the effective size
ranges between 0.2 to ranges between 0.35 to
0.4 mm and uniformity 0.55 and uniformity
coefficient between coefficient between
1.8 to 2.5 or 3.0. 1.2 to 1.8.
Rate of filtration it is small, such as 100 to it is large, such as 3000
200 L/h/sq.m. of filter to 6000 L/h/sq.m. of
area filter area.
Post treatment Almost pure water is water may be
obtained disinfected slightly to
make it completely
safe. Disinfection is a
must after RSF.

Slow sand filter Rapid sand filter
Method of Cleaning Scrapping and To clean RSF, sand is
removing of the top 1.5 agitated and
to 3 cm thick layer is backwashed with or
done to clean SSF. without compressed air.

Disinfection
The filtered water may normally contain some harmful disease producing
bacteria in int. These bacteria must be killed in order to move the water safe
for drinking, and this process of killing bacteria is known as Disinfection or
sterilization

Menthod of disinfection
1. Boiling :- The bacteria present in water can be destroyed by boiling it for
a long time.
2. Treatment with excess of lime:-Lime is used in water treatment plant for
softening. But if excess lime is added to the water, it can in addition, kill
the bacteria also.
3. Treatment with ozone:-Ozone readily breaks down into normal
oxygen, and releases nascent oxygen. The nascent oxygen is a powerful
oxidising agent and removes the organic matter as well as the bacteria
from the water.
4. Chlorination:- The chlorine enters the cell walls of bacteria and kill the
enzymes which are essential for the metabolic processes of living
organisms.

Chlorine Chemistry
Chlorine is added to the water supply in two ways. It is most often added as
a gas, Cl2(g). However, it also can be added as a salt, such as sodium
hypochlorite (NaOCl) or bleach. Chlorine gas dissolves in water following
Henry's Law.
Cl2(g) Cl2(aq) KH =6.2 x 10-2

Once dissolved, the following reaction occurs forming hypochlorous acid
(HOCl):
Cl2(aq)+H2O HOCl + H+ + Cl-

Hypochlorous acid is a weak acid that dissociates to form hypochlorite ion
(OCl-).
HOCl OCl- + H+ Ka = 3.2 x 10-8
All forms of chlorine are measured as mg/L of Cl2 (MW = 2 x 35.45 = 70.9
g/mol)

Water Treatment-Domestic

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