PURIFICATION OF WATER.pptx WATER PURIFICATION

CONTENTS
INTRODUCTION
PURIFICATION OF WATER
 LARGE SCALE
• SLOW SAND FILTERS
• RAPID SAND FILTERS
 SMALL SCALE
• BOILING
• CHEMICAL DISINFECTION
• DOUBLE POT METHOD
 CONCLUSION

INTRODUCTION
Water is essential to sustain life and a satisfactory supply must be
available to all . Improving access to safe drinking water can result in
tangible benefits to health. Every effort should be made to achieve
drinking water that is as safe as practicable

PURIFICATION OF WATER
• It can be done
On a large scale
On a small scale

LARGE SCALE PURIFICATION
• Components include
Storage
Filtration
Chlorination

1. STORAGE
During storage considerable amount of purification occurs by,
 Physical Action
90 % of suspended impurities settle down in 24 hours by gravity
 Chemical Action
Aerobic bacteria oxidizes organic matter with the help of dissolved
oxygen thus reducing the free ammonia and increasing concentration of
nitrates

Biological Action
During storage pathogenic organisms gradually die out, if
water stored for longer periods ,development of vegetable
growth such as algae. Bacterial count drops by 90% in 5-7
days
2.FILTRATION
Two types of filters are used
 Biological or slow sand filters
 Rapid sand or mechanical filters

1.SLOW SAND FILTERS
• It consist of layers of sand and gravel in a concrete or plastic
container
• Water level is maintained above sand layer
• Water layer allows bioactive layer to grow on top of the sand which
contributes to the reduction of disease causing organisms

ELEMENTS
1. Supernatant water
• Depth varies from 1 to 1.5 meters
• Provides constant head of water
• Provides waiting period for purification by sedimentation
2. Bed of graded sand
• Thickness about 1meter
• Sand grains diameter 0.2 to 0.3mm
• It is supported by a layer of graded gravel 30 to 40cm deep
which prevents the fine grains being carried into drainage
pipes
• Subjected to Mechanical straining, sedimentation, adsorption,
oxidation and bacterial action

3. An under drainage system
• Bottom of filter bed is under drainage system
• Consist of perforated pipes which not only provides an outlet
filtered water but also supports the filter medium above.
FILTER BOX : Open rectangular box, 2.5 to 4 metres deep and is
built wholly or partly below ground.
4. A system of filter control values
• To maintain a constant rate of filtration
• Venturi meter is used to measure the bed resistance or loss of
head

VITAL LAYER
• Slimy growth is formed on the surface of sand bed after a few
days of operation of the filter
• Schmutzduck layer, vital layer, zoogleal layer or biological layer
• Consist of thread like algae , plankton, diatoms and bacteria
• Heart of slow sand filters
• Removes organic matter ,holds back bacteria and oxidizes
ammoniacal nitrogen into nitrates and helps in purifying water
• 2 to 3 cm extends from top of sand bed
• Takes days to form vital layer, until it first few days filtrate is
waste
• Vital layer formation is called ripening of filter

Filter Cleaning
When bed resistance increases to such an extent regulating valve is
kept fully open, the supernatant water is then drained off and the sand
bed is cleaned by scraping off the top portion of the sand layer to a
depth of 1 to 2 cm after 20 or 30 scrapings the thickness of sand will
have reduced and a new bed is constructed

2. RAPID SAND FILTERS
• Before being subjected to rapid sand filters water has to undergo
Coagulation
Raw water is first treated with chemical coagulant such as alum
Rapid mixing
Treated water is subjected to violent agitation in a mixing chamber for
a few minutes , allows quick and through dissemination of alum through
out the bulk of water

Flocculation
It involves a slow and gentle stirring of the treated water in a
flocculation chamber for about 30 min , results in the formation of
thick copious white flocculent precipitate of aluminium hydroxide
 Sedimentation
Coagulated water is then led into sedimentation tanks where it is kept
for 2 to 6 hours
 Filtration
Partly purified water is then subjected to rapid sand filters

Filter beds
• Each filter bed unit has a surface 80 to 90metre square .Sand is
filtering medium ,size sand particle is 0.4 to 0.7mm ,depth 1m
• Below sand bed graded gravel of30 to 40 cm depth
• Depth of water above sand bed is 1 to 1.5 m
• Filtration removes the remaining alum floc not removed by
sedimentation
• As filtration proceeds the suspended impurities and bacteria clog the
filters resulting in their reduced efficiency called loss of head

Filter cleaning; back washing
• Need frequent washing depending upon loss of head
• Washing is accomplished by reversing the flow of water
through the sand bed which is called back washing
• Helps in dislodging impurities and cleaning up the sand bed
• Washing is stopped when the wash wash water is sufficiently
clean
• Whole process takes about 15 min

3.Chlorination
it’s a supplement not a substitute to sand filters
• Action of chloride
o When chlorine is added to water ,formation of hydrochloric acid and
hypochlorous acid,
o HCl is neutralized by the alkalinity of water
o Hypochlorous acid ionizes to form hydrogen ions and hypochlorite ions
o Disinfecting action is mainly due to hypochlorous acid
o Chlorine act best at ph 7

• Principles of chlorination
 The water should be clear and free from turbidity
 Chlorine demand of water should be estimated, difference
between the amount of chlorine added to the water and the
amount of residual chlorine remaining at the end of a specific
period of contact at a given temperature and ph of the water
 Point at which the chlorine demand is met is called the break point ,
if further chlorine is added beyond the break point free chlorine
begins to appear
 Free residual chlorine should be present for a contact period of
atleast one hour to kill bacteria and viruses

 Minimum recommended concentration of free chlorine is 0.5mg/l for one
hour
Sum of the chlorine demand of the water plus the free residual chlorine of
0.5mg/l constitutes the correct dose of chlorine to be applied
• Chlorine is applied either as
 Chlorine gas
 Chloramines
 Perchloron
• Break point chlorination
Addition of chlorine to water to a point at which free residual chlorine
begins to appear is called break pint chlorination

• Superchlorination
Comprises of the addition of large dose of chlorine to the
water and removal of excess of chlorine by dechlorination
method is used for heavily polluted river water
• Other agents used for water purification
 Ozonation
 Ultraviolet irradiation

SMALL SCALE PURIFICATION
• HOUSE HOLD PURIFICATION OF WATER
1. Boiling
• Water must brought to a rolling boil for 5 to 10 min
• It kills bacteria spore cyst and ova
• It removes temporary hardness
• Offers no residual protection

2. Chemical disinfection
• Bleaching powder or chlorinated lime
• Chlorine solution is prepared by mixing 4 kg of bleaching powder
with 20l of water to give a 5% solution of chlorine
• Hypochlorite or perchloron a calcium compound contains 60 to 70%
chlorine
• Chlorine tablets good for disinfecting small quantities of water
• Iodine may be used as emergency disinfection of water
• Pottasium permagnate may kill cholera vibrios but is of little use
against other disease organism

3. Filtration
• Using ceramic filters such as Pasteur chamberland filter, berkefeld
filter and katadyn filter
• Reverse osmosis is also an effective way of purifying water

DISINFECTION OF WELLS
• DOUBLE POT METHOD
Has been devised by the national environmental engineering research institute , Nagpur
India
Use of two cylindrical pot one placed inside the other
Inside height and diameter of the outer pot are 30cm and 25cm
A hole of 1cm diameter in each pot ,the inner pot hole is in the upper portion near
the rim and in outer pot it is 4cm above the bottom

 Mixture of 1kg bleaching powder and 2kg of coarse sand
is prepared and slightly moistened with water
 Inner pot is filled with the mixture upto 3cm below the level
of the hole
 Inner pot is introduced into the outer pot and the mouth of
latter is closed with polyethylene foil
 Double pot is lowered into the well by means of a rope
 Pot should be immersed atleast 1m below the water level to
prevent damage by buckets used for drawing water
 Method can be used satisfactorily for 2 to 3 weeks in a well
containing 4500l of water

CONCLUSION
• Water has a profound influence on human health. At a very basic
level a minimum amount of water is required for consumption on a
daily basis for survival and therefore access to some form of water is
essential for life. However water has much broader influences on
health and wellbeing

PURIFICATION OF WATER.pptx WATER PURIFICATION

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