Water Purification

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Purification of Water

• Dr. Jawaid Hussain
• Deptt of Community Medicine
• Assistant Professor
• Peoples Medical University of Health Sciences
  Nawabshah

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Learning Objectives

• The participant will be able to define
• Purification of Water.

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Purification Of Water

• Purification of is done by TWO ways
• Natural Methods
• Artificial Methods

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NATURAL METHODS

• Natural Method includes-
• Aeration
• Sedimentation
• Sunlight
• Dilution
• Oxidation
• Plants Animals (Aquatic)

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Artificial Methods

• They may be carried out at
• Purification of Water on Large Scale
• Purification of Water on Small Scale

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A. Purification of Water on Large Scale

• At Large scale, it is done by Filtration, which
  may be
• Slow sand filtration
• Rapid sand filtration
• Desalination

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B. Purification of Water on Small Scale /
Domestic Level

• At Small scale or Domestic level, is carried out
  by
• Boiling
• Chemical disinfection
• Filtration
• Solar radiation

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A. Purification of Water on Large Scale

• The purpose of water treatment is to produce
  water that is safe wholesome.
• The method of treatment to use depends upon the
  nature of raw water the desired standards of
  water quality.
• Ex Ground water (wells springs) may need no
  treatment other than disinfection.
• Surface water (e.g River water) which tends to
  be turbid polluted, require extensive
  treatment.
• The components of a typical water purification
  system comprise one or more of the following
  measure.

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A. Purification of Water on Large Scale

• A typical water supply carries the following
• steps in Purifying the water
• Storage
• Sedimentation
• Filtration
• Disinfection

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I. STORAGE

• Water is drawn out from the source and impounded
  in natural or artificial reservoirs.
• Storage provides of a reserve of water from which
  further pollution is excluded.
• As a result of storage, a very considerable
  amount of purification takes place.
• This natural purification we may look at it
  from three points of view

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I. STORAGE

• Physical
• By mere storage the quality of water improves.
• About 90 of the suspended impurities settle down
  in 24 hours by gravity.
• The water becomes clearer.
• This also improves the turbidity of water.
• This allow penetration of light reduce the work
  of filters.

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I. STORAGE

• (b) Chemical
• Certain chemical changes also take place during
  storage.
• The aerobic bacteria oxidize the organic matter
  present in the water with the aid of dissolved
  oxygen.
• As a result the content of free ammonia is
  reduced and a rise in nitrates occurs.

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I. STORAGE

• (c) Biological
• A tremendous drop takes place in bacterial count
  during storage due to antibiosis and oxidation.
• The pathogenic organism gradually die out.
• It is found that when river water is stored the
  total bacterial count drops by as much as 90
  percent in the first 5-7 days.
• This is one of the greatest benefits of storage.
• The optimum period of storage of river water is
  considered to be about 10-14 days.

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I. STORAGE

• (c) Biological
• If the water is stored for long periods, there is
  likelihood of development of vegetable growths
  such as algae which impart a bad smell and colour
  to water.

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II. SEDIMENTATION

• Here we add chemical coagulant Alum.
• ALUM AL2(So4)3
• The Dose is 35 mg/Litre is kept for 4 6
  hours. It is very necessary.
• Prior to filtration and helps in Preventing the
  Rapid Clogging of filter.
• The reaction is-
• Al2 (So4)3 Ca (Hco3) ? Al(OH)3 6Co2 CaSo4
• 2) Al2(So4)3 3Na2Co3 H2O ? 3NaSo4 2Al
  (OH)3 3Co2

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III. FILTRATION

• It is the oldest and Universal method of
  purification.
• Filtration is the second stage in the
  purification of water.
• This filtration reduces the bacterial content by
  98-99, turbidity by 50 PPM to 5 PPM and colour
  to colurless.

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III. FILTRATION

• There are two types of Filters
• SLOW SAND FILTERATION (BIOLOGICAL FILTER).
• RAPID SAND FILTERS ( MECHANICAL FILTERS).

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SLOW SAND FILTRATION (BIOLOGICAL FILTER)

• They are cheap and easy to design and occupy less
  space.
• Slow sand filters were first used for water
  treatment in 1804 in Scotland and subsequently in
  London.
• During the19th century their use spread
  throughout the world.
• Even today they are generally accepted as the
  standard method of water purification.

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SLOW SAND FILTRATION (BIOLOGICAL FILTER)

• They contain the concrete made basin, which
  contains the selected graded sand, supported on
  stones. The contents are
• Supernatant Water Head 1 1.5 meter for Raw
  Water
• Sand Bed, which consists of sand particles,
  supported by fine and coarse gravel.
• Drainage system
• Filter Control Valve

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1) SUPERNATANT WATER HEAD

• The supernatant water above the sand bed, whose
  depth varies from 1 to 1.5 meter, serves two
  important purpose.
• 1. It provides a constant head of water so as to
  overcome the resistance of the filter bed
  thereby promote the flow of water through the
  sand bed.
• 2. It provides waiting period of some hours (3
  to 12 hours) for the raw water to undergo partial
  purification by sedimentation, oxidation
  particle agglomeration. The level of supernatant
  water is always kept constant.

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2. SAND BED

• It is very important part of the sand bed.
• The thickness of the sand bed is a about 1 meter.
  
• The sand grains are carefully chosen so that they
  are preferably rounded and have an effective
  diameter b/w 0.2 to 0.3 mm.
• The sand should be clean and free from clay
  organic matter.
• The sand bed is supported by a layer of graded
  gravel 30 to 40 cm deep which prevents the fine
  grain being drained into the drainage pipes.

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2. SAND BED

• The sand bed presents a vast surface area, one
  cubic meter of filter sand presents some 15,000
  sq.meter of surface area.
• Water percolates the through the sand bed very
  slowly, process taking 2 hours or more.
• It is subjected to a number of purification
  processes- mechanical straining, sedimentation,
  adsorption, oxidation bacterial action, all
  playing their part.
• The designed rate of filtration of water usually
  lies b/w 0.1 to 0.4 m3/ hour/ per square meter of
  sand bed surface.

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2. SAND BED

• Vital Layer/ (Biological Filter)
• When the filter is newly laid, it acts merely as
  a mechanical strainer can not truly be
  considered as Biological.
• But very soon the surface of the sand bed gets
  covered with a slimy growth known as
  Schmuztadecke Vital Layer Zoogleal layer or
  Biological Layer.
• This layer is slimy gelatinous and consist of
  threadlike algae and numerous forms of life
  including plankton, diatoms and bacteria.

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2. SAND BED

• The formation of vital layer is known as
  ripening of the filter.
• It may take several days for the vital layer to
  form fully and when fully formed it extends for
  2-3 cm into the top portion of the sand bed.
• The vital layer is the heart of the slow sand
  filter.
• It removes organic matter, holds back bacteria
  and oxidizes ammoniacal nitrogen into nitrates
  and helps in yielding bacteria-free water.
• Un till the vital layer is fully formed, the
  first few days filtrate is usually run to waste.
• It is Scrapped, when it becomes thick.

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3. UNDER-DRAINAGE SYSTEM

• At the bottom of the filter bed is the
  under-drainge system.
• It consist of porous or perforated pipes which
  serve the dual process of providing an outlet for
  filtrated water and supporting the filter medium
  above.
• Once filter bed been laid, the under-drainage
  system can not be seen.

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FILTER BOX

• The filter box is an open box, usually
  rectangular in shape, from 2.5 to 4 meters deep
  is bulit wholly or partly below ground.
• The walls may be made of stone, brick or cement.
• The filter box consist from top to bottom
• 1.Supernatant water 1 to 1.5 meters.
• 2. Sand Bed 1.2 meters
• 3. Gravel Support 0.30 meter
• 4. Filter bottom 0.16 meter

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4. FITER-CONTROL

• Filter control is equipped with certain valves
  and devices which are incorporated in the
  outlet-pipe system.
• The purpose of these devices is to maintain a
  constant rate of filtration.

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FITER-CLEANING

• Naturally the filter may run for weeks or even
  months without cleaning.
• When the bed resistance increases to such extent
  that the regulating valve has to be kept open
  fully.
• It is time to clean filter bed, since any further
  increase in resistance is bound to reduce the
  filtration rate.
• At this stage supernatant water is drained off
  the sand bed is cleaned by scrapping off the
  top portion of the sand layer to the depth of 1
  to 2 cm.
• After several years of operation say 20 to 30
  scrapings, the thickness of the sand bed will
  have reduced to about 0.5 to 0.8 meter.
• Then the plant is closed down a new bed is
  constructed.

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ADVANTAGE OF SLOW SAND FILTRATION

• Simple to construct operate.
• The cost of construction is cheaper than that of
  rapid sand filters.
• The physical, chemical bacteriological quality
  of filter water is very high.
• It will reduce total bacterial count by 99.99
  percent E. coli by 99.9 .

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RAPID SAND FILTERS ( MECHANICAL FILTERS)

• In 1885 the first rapid sand filters were
  installed in the USA.
• Since that time, they have gained considerable
  popularity even in developing countries.
• Rapid Sand Filters are of two types
• A. Gravity type (e.g Patersons Filter)
• B. Pressure type ( Candys Filter)
• Both types are in use.
• Following steps are involved in the purification
  of water by Rapid Sand Filters.

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RAPID SAND FILTERS ( MECHANICAL FILTERS)

• Following steps are involved in the purification
  of water by Rapid Sand Filters.
• 1. COAGULATION
• The raw water is first treated with a chemical
  coagulant such as alum.
• The dose of alum varies from 5-40 mg or more per
  liter, depending upon the turbidity colour,
  temperature and the pH value of water
• 2. RAPID MIXING
• The treated water is then subjected to violent
  agitation in a mixing chamber for few minutes.
• This allows a quick and thorough dissemination
  of alum throughout the bulk of water, which is
  very necessary.

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RAPID SAND FILTERS ( MECHANICAL FILTERS)

• 3. FLOCCULATION
• The next phase involves a slow gentle stirring
  of the treated water in a Flocculation Chamber
  for about 30 minutes.
• The mechanical type of flocculation is the most
  widely used.
• It consist of a number of paddles which rotates
  at 2 to 4 rpm with the help of motors.
• It results in the formation of thick, copious,
  white flocculent precipitate of aluminum
  hydroxide.
• The thicker the precipitate or flock diameter,
  the greater the setting velocity.

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RAPID SAND FILTERS ( MECHANICAL FILTERS)

• 4.SEDIMENTATION
• The coagulated water is now led into
  sedimentation tanks where it is detained for
  periods varying from 2-6 hours, when the
  flocculent precipitate together with impurities
  bacteria settle down in the tank.
• At least 95 of the flocculent precipitate needs
  to be removed before the water is admitted into
  the rapid sand filters.
• The precipitate or sludge is which settles at the
  bottom is removed from time to time without
  disturbing the operation of the tank.

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RAPID SAND FILTERS ( MECHANICAL FILTERS)

• 4.SEDIMENTATION
• For proper maintenance the tank should be cleaned
  regularly from time to time, otherwise they may
  become a breeding ground for molluscs and
  sponges.
• 5.FILTERATION
• The partly clarified water is now subjected to
  rapid sand filters.

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RAPID SAND FILTERS ( MECHANICAL FILTERS)
Chlorine
River Water
Consumption
Fitters
Mixing Chamber
Clear water storage
Flocculation Chamber
Sedimentation Tank
Alum
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FILTER BEDS

• Each unit of filter bed has a surface of about 80
  to 90 m2 (900 sq. feet).
• Sand is the filtering medium.
• The effective size of the sand particles is b/w
  0.4 to 0.7 mm.
• The depth of the sand bed is usually about 1
  meter.
• Below the sand bed is a layer graded gravel 30 to
  40 cm deep.
• The gravel supports the sand bed and permits the
  filtered water to move freely towards under the
  drain.

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FILTERATION

• As filtration proceeds, the alum-floc not
  removed by sedimentation is held on the sand bed.
• It forms a slimy layer layer comparable to the
  Zoogleal layer in the slow sand filters.
• It absorbs bacteria from the water effects the
  purification.
• Oxidation of ammonia takes place during the
  passage of water through the filters.
• As filtration proceed the suspended impurities
  and bacteria clog the filters.
• The filters soon become dirty begin to loose
  their efficiency.

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FILTERATION

• When the loss of head approaches 7-8 feet,
  filtration is stopped the filters are subjected
  to a washing process known as Back Washing.

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BACK WASHING

• Rapid sand filters need frequent washing daily or
  weekly depending upon the loss of head.
• Washing is accompanied by reversing the flow of
  water through the sand bed which is called Back
  Washing.
• It removes impurities cleans the sand bed.
• The whole process of washing takes about 15
  minutes.
• In some rapid sand filters compressed air is used
  as part of back washing.

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ADVANTAGE OF RAPID SAND FILTRATION

• Rapid sand filter can deal with raw water
  directly. No preliminary storage is required.
• The filter bed occupy less space.
• The initial cost is high but becomes cost
  effective in future.
• Filtration is rapid, 40 to 50 times that of slow
  sand filters.
• The washing of the filters is easy.
• There is more flexibility in operation.

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METHOD OF CHLORINATION

• For disinfection on large scale water chlorine
  is applied either as
• Chlorine Gas.
• Chloramines.
• Perchloron.
• Chlorine gas is the first choice , bcz it is
  cheap, quick in action, efficient and easy to
  apply.
• But chlorine gas is an irritant to the eyes
  poisonous.
• A special Chlorination equipment known as
  Patersons chloronome is required for measuring,
  regulating and administration of chlorine gas to
  water.

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DISINFECTION/ CHLORINATION

• Chlorination is one of the greatest advances in
  water purification.
• It is supplement, not a substitute to sand
  filtration.
• Chlorine kills pathogenic bacteria, but it has no
  effect on spores certain viruses (e.g Polio,
  viral hepatitis).
• Apart from its germicidal effect, chlorine has
  several important secondary properties in water
  treatment.
• It oxides' iron, manganese hydrogen suphide.
• It also helps in destroying some odour producing
  constituents, so improves the taste and odour.
• It controls algae and slim organisms acid
  coagulation.

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USE OF CHLORINE IN PURIFICATION OF WATER

• Chlorine can be used in different ways to purify
  the water.
• Simple Chlorination
• Chloramination
• Super chlorination followed by Dechlorination

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SIMPLE CHLORINATION

• When Chlorine is added to water, there is a
  formation of hypochloric hypochlorous acids.
• The hypochloric acid is neutralized by the
  alkalinity of the water.
• The hypochlorous acid ionizes to form hydrogen
  ions hypochlorite ions.
• H2O Cl2 HCl HOCL
• HOCl H OCL
• The disinfection action of chlorine is mainly due
  to the hypochlorous acid due to small extent
  due to the hypochlorite ion.
• Hypochorous acid is the most effective form of
  chlorine for water disinfection.

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SIMPLE CHLORINATION

• Chlorine acts best as a disinfection when the pH
  of water is around 7 bcz of predominance of
  hypochorous acid.
• When the pH value exceeds 8.5 it is un reliable
  as a disinfectant because about 90 of the
  hypochlorous acid gets ionized to hypochlorite
  ion.

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CHLORAMINATION

• In this process NH3 is added to water First and
  is followed by addition of Chlorine.
• It exerts its effect on bacteria by forming
  chloramines.
• The contact time must be 2 hours.
• These are more effective and stable for longer
  period of time.
• The Ratio of NH3 to Cl2 is 14 or 15

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BREAK POINT CHLORINATION

• The addition of chlorine to ammonia in water
  produces chloramines which do not have same
  efficiency as free chlorine.
• Further addition of chlorine in water will cause
  reduction in residual chlorine due destruction of
  total chloramines by added chlorine.
• The end product do not represent any residual
  chlorine.
• This fall in the residual chlorine will continue
  with further increase in chlorine dose after a
  stage the residual chlorine begins to increase in
  proportion to the added dose of chlorine.

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BREAK POINT CHLORINATION

• This point at which the residual chlorine appears
  when all combined chlorine have been destroyed
  is Break point chlorination.
• Now here if further Cl2 is added this will cause
  rise in Residual Cl2 (May be free or combined).
• This is direct proportion to chlorine added.

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Break Point Chlorination
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SUPERCHLORINATION FOLLOWED BY DECHLORINATION

• Super chlorination followed by Dechlorination
  comprises the addition of large doses of chlorine
  to the water and removal of excess chlorine after
  disinfection.
• Here we add excessive Cl2. After a suitable
  contact time, this Cl2 is removed by addition of
  sulphur Dioxide in the Ratio of 18.
• This procedure satisfies the Cl2 demand of water
  and kills cysts, ova and bacteria which are not
  killed in ordinary chlorination.
• This method is applicable to heavy polluted
  waters, whose quality fluctuates greatly.

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PRINCIPLES OF CHLORINATION

• First of the all, the water to be chlorinated
  should be clear should be free from turbidity.
  Turbidity impedes efficient chlorination.
• Chlorine demand of water should be estimated.
• Contact period. The presence of free chlorine for
  a contact period of at least one hour is
  essential to kill bacteria viruses.
• Chlorine has no effect on spores, protozoal cyst,
  helminthic ova, except in higher doses.
• The minimum recommended concentration of free
  chlorine is 0.5 mg/Liter for one hour.
• The free residual chlorine provides a margin of
  safety against microbial contamination which may
  occur during storage distribution.

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B. Purification of Water on Small Scale

• At Small scale or Domestic level, is carried out
  by
• Boiling
• Chemical disinfection
• Filtration
• Solar radiation

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i. BOILING

• It is satisfactory method of purifying water for
  house hold purposes.
• To be effective the water must be brought to a
  rolling boil for 10 to 20 minutes.
• It kills all bacteria, spores, spores, cyst
  yields sterilized water.
• Boiling also removes temporary hardness by
  driving off carbon dioxide precipitating the
  calcium carbonate.
• The taste of water is altered, but this is
  harmless.

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ii. CHEMICAL DISINFECTION

• 1. Blenching Powder
• Bleaching powder or chlorinated lime (CaOCl2) is
  a white amorphous powder.
• When freshly made it contains about 33 of
  available chlorine.
• It is however unstable compound.
• On exposure to air, light moisture, it rapidly
  losses its chlorine content.
• But when mixed with lime it retains its strength
  known as stabilized bleach.
• Bleaching should be stored in a dark, cool, dry
  place in a closed container.

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ii. CHEMICAL DISINFECTION

• 2. Blenching Powder
• The principle in chlorination is to ensure a free
  residual chlorine of 0.5 mg/L at the end of one
  hour contact.
• Highly polluted turbid waters are not suited
  for direct chlorination.

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ii. CHEMICAL DISINFECTION

• 2. Chlorine Solution
• Chlorine solution may be prepared from Bleaching
  powder.
• If 4 kg of bleaching powder with 25 available
  chlorine is mixed with 20 liters of water, it
  will give a 5 solution of chlorine.
• Ready-made chlorine solution in different
  strengths are available in the market.
• Like bleaching powder, the chlorine solution is
  subject to losses on exposure to light or on
  prolong storage.
• Bleaching should be stored in a dark, cool, dry
  place in a closed container.

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ii. CHEMICAL DISINFECTION

• 3. Chlorine tablets
• Under various trade names ( E.g Halozine Tab are
  available in the market.
• They are good for disinfecting small quantities
  of water.
• A single tablet of 0.5 g is sufficient to
  disinfect 20 liters of water.

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ii. CHEMICAL DISINFECTION

• 4. Iodine
• Iodine may be used for emergency disinfection of
  water.
• 2 drops of 2 ethanol solution of iodine will be
  sufficient for one liter of water.
• A contact time of 20 to 30 minutes is needed for
  effective disinfection.
• Iodine is unlikely to become a municipal water
  supply disinfectant in a broad sense.
• High cost the fact that the element is
  physiologically active (Thyroid activity) are its
  major disadvantages.

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ii. CHEMICAL DISINFECTION

• 5. Potassium Permanganate
• Once it was widely used, but now it is no longer
  recommended for water disinfection.
• Although a powerful oxidizing agent, it is not a
  satisfactory agent for disinfecting water.
• It may kill Vibrios Cholera but have little
  effect on other organism.
• It has other drawbacks such as altering the
  colour, smell taste of water.

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iii. FILTERATION

• Water can be purified on a small scale by
  filtering through ceramic filters such as Pastuer
  Chamberland filter, Berkefeld Filter Katadyn
  Filter.
• Filter candles usually remove bacteria found in
  drinking water but not the filter-passing
  viruses.
• Filter candles are liable to be logged with
  impurities bacteria.
• They should be cleaned by scrubbing with a hard
  brush under running water.
• Only clean water should be used with ceramic
  filters.

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Assurance of water quality

• This is done by FOUR ways
• Physical examination
• Chemical examination
• Bacteriological examination
• Radiological examination

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Physical examination

• In this we see for
• Turbidity lt 5 nephelometric turbidity unit
• Colour 15 True colour unit (TCU)
• Taste and odour (should be palatable)
• Temperature cool
• No smell

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Chemical Examination

1. PH 6.5 8.5
2. Chloride 250 mg/Litre
3. Iron .3 mg/litre
4. Na 200 mg/Litre
5. Hardness 200 mg/litre
6. Copper 1 mg/litre
7. Zinc 3 mg/litre
8. Arsenic .01 mg/litre
9. Lead .01 mg/litre

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Bacteriological Examination

• It should be free from bacteria, viruses and
  helminths and protozoa
• To see for bacterias we perform
• Presumptive Coliform test It is done on
  McConkeys media for 48 hours
• We take

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a) Presumptive Coliform test Bacteriological
Examination

• i) 50 ml of H2O to 50 ml of D.S medium 1
• tube
• ii) 10 ml of H2O to 10 ml of D.S medium 5
• tubes
• iii) 1 ml of H20 to 5 ml of D.S medium 5
• tubes
• iv) 1 ml of H2O to 5 ml of D.S medium 5
• tubes

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Presumptive Coliform test Bacteriological
Examination

• Presence of acid and gas confirms the presence of
  E.coli. Those who grow at 37C ? N. Faecal
  E.coli, Those who grow at 44 C ? Faecal E.coli.

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b) Colony Count

• It is done on Agar plate by taking 1ml of water
• At 22C for 72 hour 20-100 colonies
• At 37C for 48 hour 0-10 colonies, will prove
  that water is potable.

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Radiological Examination

1. Alpha photon emitter 15 pci/litre
2. Beta Photon emitter 4 m ram / y
3. Combined radium 5 Pci/litre

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WHO Criteria for Water

1. No sample should have E. coli in 100 ml of water
2. Not gt 3 Coliform should be present in 100 ml of
   water
3. Not gt 5 of sample through out the year should
   have coliform in 100 ml of H2O
4. No TWO consecutive sample should have coliform in
   100 ml of water