disinfection and fluoridation are an necessary steep for water

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2. Ministry of higher education
Baghlan university
Engineering faculty
Civil dept.
Disinfection and Fluoridation
Presents by: Group (10 )
Prof. in charge: Misaq ahmad (muradi)
(Date: 2019/6/19)
19/6/2019
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3. Presents by:
Ehsanullah (Sultani) Mohammad mukhtar
(murzaee)
Sayed omid (aqbaly)
Mohammad Reza
(Rahimi)
Mohammad Abid
(Mohammadi)

4. Outlines
 Introduction
 Disinfection
 Emergency disinfection
 Fluoridation
 Operation and maintenance
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5. Introduction
 Disinfection is used in water treatment to reduce pathogens to an
acceptable level.
 Disinfection is not the same as sterilization. Sterilization implies the
destruction of all living organisms.
 Drinking water does not need to be sterile to be safe to drink.
 Three categories of human enteric pathogens are of concern in
drinking water: bacteria, viruses, and amebic cysts. Disinfection must
be capable of destroying all three.

6. 1.DISINFECTION
1.1.Disinfection Chemistry
 Chlorine is the most common disinfecting chemical used.
 The term chlorination is often used synonymously with disinfection.
 Chlorine may be used as an element (Cl 2 ), as sodium hypochlorite
(NaOCl), also known as bleach, as calcium hypochlorite [Ca(OCl)2 ],
also known as HTH R , or as chlorinated lime (CaOCl2 ).
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7. 1.Disinfection………. contd
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8. 1.2.Chemical Disinfectant Kinetics
Although more complex models are available, it is often assumed that
decay of chlorine, combined chlorine, and chlorine dioxide can be
modeled as a first order or pseudo-first order reaction, that is:
𝑑𝑐
𝑑𝑡
= −𝑘 𝑑 𝑐
 where C disinfectant concentration, mg/L
 kd = first order decay rate constant, time 1
 t= time, complementary units to kd
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9. 1.2.Chemical Disinfectant
Kinetics….Contd
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10. 1.3.Chemical Oxidant Demand
 The chlorine demand of a water is the difference between the
amount of chlorine added and the amount of free, combined or total
chlorine remaining at the end of the contact period.
 Significant amounts of ammonia in the water react with chlorine to
produce an unpleasant taste and odor (T&O).
 One method for removing T&O is by the addition of chlorine in a
process called breakpoint chlorination.
 The reactions of chlorine and ammonia exhibited in breakpoint
chlorination are an illustration of chlorine demand ( Figure 13-2 ).
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11. 1.4.Mechanisms of Disinfection
 The mode of action by which disinfectants inactivate or kill
microorganisms is dependent on a large number of varia bless.
 This brief overview is limited to some of the common water
disinfectants and two broad classes of microorganisms: bacteria and
viruses.
1.4.1.Disinfection Kinetics
1.Chick’s Law
Using disinfectants like phenol, mercuric chloride, and silver nitrate and
organisms like Salmonella tophi, Escherichia coli, Staphylococcus aurous,
and Bacillus anthraces, Dr. Harriet Chick demonstrated that disinfection
could be modeled as a pseudo-first order reaction with respect to the
concentration of organisms (Chick, 1908).
𝑑𝑁
𝑑𝑡
= −𝑘 𝑐N
o where N number of organisms per unit volume
o kc= rate constant of inactivation, s 1 , or min 1
o t= time, s, or min
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12. 1.5.Disinfection Practice
To be of practical use, disinfectants must possess the following properties:
 1. They must destroy the kinds and numbers of pathogens that may
be introduced into. water within a practicable period of time over an
expected range in water temperature.
 2. They must meet possible fluctuations in composition,
concentration, and condition of the water to be treated.
 3. They must be neither toxic to humans and domestic animals nor
unpalatable or otherwise objectionable in the concentrations
required for disinfection.
 4. Their strength or concentration in the treated water must be
determined easily, quickly, and, preferably, automatically.
 5. Their cost must be reasonable.
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13. 1.5.Disinfection Practice……
Ideally, disinfectants should also possess the following characteristics:
 1. They should be safe and easy to store, transport, handle, and
apply.
 2. They should persist in a sufficient concentration to provide
reasonable residual protection against possible recontamination
before use, or—because this is not a normally attainable property—
the disappearance of residuals must be a warning that
recontamination may have taken place.
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14. 1.6.Regulatory Context
Selection of an appropriate disinfection strategy for water treatment
requires a balance among three driving forces:
• Providing water free of pathogens. The regulatory focus for pathogen
removal is on coliform bacteria, heterotrophic plate counts,
Cryptosporidium oocysts, Giardia cysts, Legionella, and viruses.
• Avoiding production of disinfection byproducts (DBPs). Trihalomethanes
(THMs), haloacetic acids (HAAs), other halogenated organic compounds,
ozone DBPs, oxidation byproducts, and disinfectant residuals present a
health risk. They must be limited in drinking water.
• Maintaining a disinfectant residual in the distribution system. Residual
disinfectant is provided to maintain the bacteriological quality, provide a
rapid means for detection of system contamination, and prevent
regrowth of microorganisms.
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15. 1.7.Weight Percent Chlorine
The weight percent chlorine is a measure of the amount of chlorine
being purchased or being supplied.
Weight=
GMW of chlorine in compound
GMW of compound
(100%)
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16. 1.8.Disinfection Design
Ultimately the agency that administers drinking water regulations will
determine the required Ct requirements and the credits that will be
given for various treatment steps. The following steps can be taken to
determine the probable credits:
1. Determine the total removal/inactivation required.
2. Determine the credits for physical removal.
3. Determine the credits required for inactivation by disinfection.
4. Select the disinfectant.
5. Determine the required Ct to achieve the required inactivation for
the design conditions (pH, temperature).
6. Compute t10 for the water to reach the first customer.
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17. 1.9.EMERGENCY DISINFECTION
 When disasters such as floods, tornadoes, and hurricanes occur or
when the water treatment plant disinfection system fails, emergency
precautions are required to prevent widespread disease.
 In the case of disruption of the water treatment plant disinfection
system, loss of water pressure due to a break in the water main, or
similar circumstances, the water utility will announce a boil water
advisory notice.
 Boiled water should be stored in containers cleaned with boiled water
or disinfected water.
 For extended durations without public water supply, advisories should
also include instructions to bury fecal waste and to wash hands in
disinfected or boiled water.
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18. 2.Fluoridation
2.1.introduction
 When the concentration of naturally occurring fluoride is too
low to prevent tooth decay, it is added into the water supply.
 When it produces mottling because it is too high, it is
removed from the water.
 The discussion in this chapter is focused on increasing the
concentration to prevent tooth decay.
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19. 2.2.Fluoridation Chemistry
 The three most commonly used fluoride compounds are sodium
fluoride (NaF), fluorosilicic acid (H2 SiF6 ), and sodium fluorosilicate
(Na2 SiF6 ).
The American Water Works Association (AWWA) standards for these
compounds are:
 AWWA Standard B701 for sodium fluoride.
 AWWA Standard B702 for sodium fluorosilicate.
 AWWA Standard B703 for fluorosilicic acid.
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20. Brief History of Fluoridation
 By the early 1900s it was noticed that inhabitants of some areas of
the United States, especially parts of Colorado and Texas, had
mottled teeth (dental fluorosis), and that children with fluorosis
tended to have fewer cavities.
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21. 2.3.Fluoridation Practice
2.3.1.Dosage
 The dosage is the amount of fluoride chemical to achieve the
optimum fluoride level to prevent tooth decay.
 Initially, the level was obtained by examination of the teeth of
thousands of children living in various places with different fluoride
levels.
 Early in the investigation the variation was linked to the local air
temperature, which had a direct bearing on the amount of water
children consumed at different ages (Reeves, 1999).
Dosage = 8× 10−4 𝑇 − 5.82 × 10−2 𝑇 + 1.7432
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22. 2.4Feed Systems
 The simplest fluoridation system is based on fluorosilicic acid. The acid is
supplied in carboys. These are set on a platform scale, which is used to
monitor the dose.
 Piston, diaphragm, or peristaltic pumps made of polyvinyl chloride (PVC) or
polypropylene are used to inject the fluorosilicic acid into the main water
flow.
 A sodium fluoride saturator ( Figure 13-15 ) is a simple system that may be
used for plants up to 50,000 m3 /d. Sodium fluoride from bags is transferred
into the tank and dissolved. The pump selection and use of a vacuum breaker
is the same as that for fluorosilicic acid.
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23. 2.5.Feed Point
 Fluoride compounds must be fed after conventional filtration or
softening.
 Feeding fluoride compounds upstream of coagulation/flocculation,
settling, and filtration results in a significant decrease in TOC
removal, clarifier performance, overloading of the filter and loss
of up to 40 percent of the applied fluoride dose .
 In softening plants the fluoride will precipitate as CaF if it is
introduced before filtration of the softened water.
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24. 2.6.Safety Precautions
 The greatest chance for exposure to dry fluoride chemicals comes from
the inhalation of dust generated when feeder hoppers are being filled.
The fumes from fluorosilicic acid are extremely toxic.
 During filling operations, operators must wear a respirator approved by
the National Institute for Occupational Safety and Health (NIOSH),
splash-proof safety goggles, an apron, and rubber gloves.
 A deluge shower and eyewash should be installed in the room where
fluoridation chemicals are used or stored.
 Air exhausted from the fluoride handling equipment shall discharge
through a dust filter to the outside atmosphere of the building (GLUMRB,
2003).
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25. 2.7.Operation and maintenance
The following activities are typical:
 Routine measurement of residuals both in the plant and the
distribution system to ensure compliance with applicable
regulations.
 Daily, weekly, and monthly preventive maintenance is essential
as the chemicals are corrosive and materials failure can result in
catastrophic injury and damage to facilities.
 Corrective action drills and maintenance of response equipment
and materials for chemical leakage.
 Periodic “hands-on” safety training.
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26. conclusion
 Disinfection is used in water treatment to reduce pathogens
to an acceptable level.
 Chlorine is the most common disinfecting chemical used.
 When the concentration of naturally occurring fluoride is too
low to prevent tooth decay, it is added into the water supply.
 The simplest fluoridation system is based on fluorosilicic
acid. The acid is supplied in carboys. These are set on a
platform scale, which is used to monitor the dose.
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27. Reference
 Mackenzie L. Davis, Ph.D., P.E., BCEE, WATER AND
WASTEWATER ENGINEERING, Copyright © 2010 by
The McGraw-Hill Companies.
 Joel M. Kauffman, Ph. D, Water Fluoridation,2005.
 A Review of U.S. Disinfection Practices and Issues,
Drinking Water Chlorination
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28. Questions????
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