This document summarizes different methods of disinfecting water, including chlorination, ozonation, treatment with lime, iodine, bromine, ultraviolet rays, potassium permanganate, silver, and boiling. It provides details on the chemical processes involved, advantages, and disadvantages of each method. Chlorination is described as the most commonly used and effective method, involving the addition of chlorine to water to form hypochlorous acid and hypochlorite ions which kill bacteria. The ideal pH for chlorination is below 7 to maximize the amount of hypochlorous acid present.

1. Govt. college of Engineering,
Aurangabad
DISINFECTION
Presented by
Nikhil Holsamudrkar
Shashank Karyakarte
Sidharth Kasliwal
BE11F01F017
BE11F01F021
BE11F01F059
Guided by
Prof. P. A. Sadgir

2. Disinfection
 The filtered water which is obtained by various filtration
processes contains harmful diseases producing bacteria,
these bacteria must be killed to make the water safe for
drinking
 The chemical used for killing these bacteria are known as
disinfectants and the process is known is known as
disinfection

3.  The presence of turbidity’s, colour, minerals etc may not be
dangerous but the presence of even single harmful organism
will be definitely dangerous thereby making disinfection as
the most important process. The disinfection not only
removes the existing bacteria from the water at the plant but
also ensures their immediate killing even afterwards in the
distribution system. The contamination of water during its
transit from the treatment plant to the place of its
consumption is also thus, prevented by disinfectants.

4. Materials used as disinfectants should be :1. Able to give residual sterilizing effect for long period
2. Should be harmless, unobjectionable to tongue,
economical, measurable by simple test.
3. Minor methods of disinfections
4. Boiling of water
5. Bacteria get killed due to boiling
6. Effective but not practically possible for public water
supplies
7. Kills existing germs but do not take care of future
contamination

5. Treatment with Lime
 Addition of excess lime kills bacteria in it
 Addition of 14-43 ppm of excess lime has been found to
remove the bacterial load by about 99.3-100% from highly
polluted waters
 Bacteria gets killed due to increased pH value resulted by
the addition of various lime
 Disadvantages
 Cannot protect water from recontamination, hence not
used. Treatment like recarbonation for the removal of excess
lime for the further purification of water need to be done
hence not useful

6. Treatment with Ozone
 Ozone gas is unstable allotropic form of oxygen, with each
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of its molecules containing three oxygen items.
It can be produced by passing high tension electric current
through the stream of air in a closed chamber
Reaction
3O2 under high electric arc voltage 2O3
Ozone breaks down into nascent oxygen as
O3
O2 + O
The nascent oxygen so produced is powerful oxidizing agent
and removes the organic matter and bacteria from water.

7. Advantages:
 Ozone being unstable nothing remains in water by the
time it reaches in water to distribution system.
 Ozone removes the colour, taste and odour from
water in addition to removing bacteria from it.
 The ozonized water becomes tasty and pleasant unlike
the chlorinated water which becomes bitter to tongue.
Disadvantages
 It is much costlier than chlorination
 It needs electricity for its manufacture and hence can
be used when electricity is available easily and cheaply
 No residuals can be maintained because it is highly
unstable and hence it does not ensure safety against
possible contamination.

8. Treatment with iodine and bromine
 The quantity of this disinfectants may be limited to about
eight ppm and contact period of five minutes is generally
enough. These disinfectants are now a days are also
available in form of pills and are thus very handy.
 They are not used for treating any large scale public
supplies but may be used for treating small water
supplies for army troops, private plants, swimming pools
etc.

9. Treatment with ultraviolet rays
 Ultraviolet rays are invisible rays having wavelength 1000-
4000 mµ
 And can be produced by passing electric current through
mercury enclosed in quartz bulbs.
 The water to be treated with ultraviolet rays should,
however, be less turbid and low in colour. Normally it
should be colourless and turbidity should not exceed 15
mg/l
 The depth of water over the bulbs should not generally
exceed 10cm or so because these rays can effectively
penetrate through this much distance only.

10. Advantages
 Sterilization with UV rays does not impart any addition
taste or odour to water , as no chemicals are added.
 The method possesses ample scope for treating small
quantities of water in hospitals and dispensaries for
surgical uses or for drinking purposes for the place
where cost is minor factor.
Disadvantages
 Method is very costly, needs technical knowhow, and
possesses possibilities of interruption due to failure of
electricity.

11. Treatment with potassium permanganate
 This is used as popular disinfectant for disinfecting well
water in villages which are generally contaminated with
lesser amount of bacteria. Normal doses of this
disinfectant varies between 1-2mg/l with a contact
period of 4-6hrs.
 Advantages
 Besides killing bacteria it also helps in oxidizing the taste
producing organic matter hence it is added in small doses
to chlorinated water also.
 It has also been used as an algaecide and for removing
colour and iron from water.

12. Disadvantages
 Potassium permanganate though cheap , handy and useful
yet can’t guarantee 100% removal of bacteria.
 It can possibly remove organisms causing cholera , but is of
little use against other disease organisms.
 Water treated with potassium permanganate with the
passage of time , produces a dark brown precipitate , which
is noticeable as a coating on porcelain vessels and is difficult
to remove without scouring.

13. Treatment with silver or electro-Kateldyn
process
 In this method of disinfection metallic silver ions are
introduced into the water by passing it through a tube
containing solid silver electrodes which are connected to a
DC supply of about 1.5 volts.
 The recommended silver dose may vary between 0.05 to
0.1 mg/l , and the required contact period may vary
between 15 minutes to 3 hrs.

14. Advantages
 The silver treatment neither imparts any taste and odour to
water nor it produces any harmful effects on human body.
 The method removes algae and its germicidal property is
retained for a considerable time, thus allowing some
safeguard against future contamination
Disadvantages
 Use of silver is very costly and hence not adopted for
treating for public supplies.
 Suspended organic matter and hydrogen sulphide should be
removed before using this disinfectant hence it adds to cost
of disinfection.

15. Chlorination
 When chlorine is added to water, it forms hypochlorous acid
or hypochlorite ions, which have an immediate and disastrous
effect on most forms of microscopic organisms.
PH > 5
 Cl2 + H2O
HOCL + HCL
 The hypochlorous acid is unstable and may break into
hydrogen ions and hypochlorite ions
PH >8
 HOCL
H+ + OCLPH<7
n

16.  Thus, at PH values greater than 10, only OCL ions are found;
while in ph values of less than 7(more than5), HOCL will
generally exist without dissociating into OCL ions; and in the
PH range below 5, chlorine does not react and remains as
elemental chlorine.
 Out of these forms of free available chlorine, the
hypochlorous acid is the most destructive, being about 80
times more effective than hypochlorite ions. For this reason,
the PH value of water during chlorination is generally
maintained slightly less than 7, so as to keep the dissociation
of HOCL to minimum, and thereby keeping more HOCL in
solution compared to OCL ions.