1. WATER THAT IS SUITABLE FOR
DRINKING IS CALLED POTABLE WATER.
2. 1. Screening
2. Sedimentation
3. Coagulation
4. Filtration
5. Disinfection of water
3. In order to remove floating impurities
screening is carried out. screens of different
kinds such as Bar screen, drum screen, and
micro screeners are employed. These screens
retain any floating impurity and are cleaned.
4. Sedimentations a process of removing suspended
impurities by allowing the water to stay undistributed
for some time in large tanks when most of suspended
particles settle down due to force of gravity. The
accumulation of the debris at the bottom of tank is
periodically scraped and removed.
•The velocity with which a particle in water falls under
the action of gravity depends upon following factors:
•The horizontal flow of velocity of water
•The size of particle
•Temperature of water
5. Coagulation is a process of removing colloidal
particles from water by addition of certain
chemicals known as coagulants before
sedimentation.
Colloidal particles present in water either do not
settle down at all or take a very long time.
These coagulants reacts with bi-carbonates present
in water and form bulky gelatinous precipitate
called flock.
Colloidal particles are very small sized particles
possessing either positive or negative charge.
colloidal particles of clay possess negative charge.
9. •Filtration is a process of removing insoluble colloidal
and bacterial impurities by passing water through a
bed of proper sized material.
•It consists of a large shallow rectangular tank made of
concrete. At the bottom of the tank, there is a channel
of brick through filtered water goes out.
•The rate of filtration after 24 hours of use becomes
slow due to clogging of pores of sand layer is scrapped
off and replaced by a new sand layer. And the
scrapped sand is reused.
•These filters are also best for municipal water supply
and the scrapped sand is re-used after washing with
water.
10. •Body aid is used when the slurry is low in solids content with
fine and slimy particles that are difficult to filter. To enhance
filtration coarse solids with large surface area are added to the
slurry and serve as a body-aid that captures and traps in its
interstices the slow filtering particles and produce a porous
cake matrix. The amount added depends on the nature of the
solids and varies from ½ for non-compressible and up to 5
times for gelatinous solids.
•Precoating the plates with a 2-3 mm thick medium of a known
permeability and its application requires skills since it takes-up
effective cake volume, lengthens the cycle time and an over
consumption can be quite costly
The following materials serve as body-aid or are used to form a
precoat:
Diatomaceous Earth (also called Diatomite) consisting of
silicaceous skeletal remains of tiny aquatic unicellular plants.
Perlite consisting of glassy crushed and heat-expanded rock
from volcanic origin.
Cellulose consisting of fibrous light weight and ash less paper
like medium.
Special ground wood is becoming popular in recent years since
it is combustible and reduces the high cost of disposal. There
are nowadays manufacturers that grind, wash and classify
special timber to permeability's which can suit a wide range of
applications.
11. The disinfection of water can be carried out by
following methods:
Boiling
Chlorination
Aeration
Removal of algae
Ultraviolet rays
ozonisation
12. Water disinfection means the removal, deactivation or killing of
pathogenic microorganisms. Microorganisms are destroyed or
deactivated, resulting in termination of growth and reproduction.
When microorganisms are not removed from drinking water,
drinking water usage will cause people to fall ill.
Sterilization is a process related to disinfection. However, during the
sterilization process all present microorganisms are killed, both
harmful and harmless microorganisms.
