Disinfection methods in water treatment process.

1. Anup Ghimire
Rock Face Limited

2. Common microorganisms in
water
 Bacteria
such
as
E.coli,
leptospira
species, salmonella species, shigella and vibrio
chollrae

3. Common microorganisms in water
 Protozoa
such
as
Balantidium
coli,
Cryptospiridium parvum, Entamoeba histolytica
and Giardia lambia

4. Common microorganisms in
water
 Helminths such as Ascaris lumbricoides, T.
solium and Trichuris trichuria

5. Common microorganisms in water
 Viruses such as Entero viruses, Hepatitis A virus
and Rota virus

6. Water treatment
 Conventional methods of water treatment can’t
remove some pollutants
concentrations in water.
persistent
at
lower

7. Water treatment
 Disinfection process removes microorganisms from
drinking water.
 Ozonation, Chlorination and UV-radiation are
effective disinfection methods.

8. Ozonation
 Ozone is highly corrosive and toxic colourless gas
and powerful oxidant capable of oxidising organic
and inorganic compounds in water.

9. Ozonation
 Ozone is formed by combining an oxygen atom with
oxygen molecule (O2).

10. Ozonation
 Ozone reacts with substrate or organic and inorganic
compounds by direct oxidation and oxidation of
compounds by hydroxyl free radicals.

11. Ozonation: applications
 Bleaching process
 Drinking water treatment such as improvement
of flocculation,
removal
de
coloration,
taste/odour

12. Ozonation: applications
 Waste water treatment processes such as elimination
of tensides, phenols, COD, cyanides and sludge
reduction.

13. Ozonation: applications
 Process water such as cooling water, swimming pools
and product polishing such as chemical modification
of food and shelf-life improvement of food.

14. Ozonation: applications
 Water treatment process to remove bacteria,
viruses, organic and inorganic pollutants and
hazardous chemicals.

15. Ozonation: applications
 Ozonation process is also applied in the treatment of
waste water contaminating milk and
chemically treated municipal wastewater.
physico-

16. Ozonation
 Ozone attacks bacterial membrane either through the
glycoproteins or glycolipids or through certain amino
acids and ozone reacts with nuclear material affecting
pyrines and pyrimidine in nucleic acids.

17. Ozonation
 Ozone acts on viral capsid to inactivate viruses and
high concentration of ozone dissociates the capsid
completely.

18. Ozonation
 Ozone inactivates RNA and DNA of the viruses.
 Protein capsid is affected by ozone attack which
releases nucleic acid and inactivates DNA.

19. UV radiation
 Disinfection from UV radiation removes organic
compounds.
 No
production of
compounds (VOCs).
odour and
volatile organic

20. UV radiation
 Improves taste of water.
 Do not require storage of hazardous waste and
requires minimal space for treatment.

21. UV radiation
 Growth and reproduction of micro-organism is
inhibited by UV light induced genetic material
disruption.

22. UV radiation
 UV light is capable of penetrating microbe’s cell wall
without producing toxic side effects.
 Optimum wave length requirement to destroy
bacterial activities lies between 250nm to 270nm.

23. UV radiation
 Special lamp to produce a spectrum of radiation is
used in disinfection process.

24. UV radiation
 Presence of high levels of suspended solids,
turbidity, colour and soluble organic matter creates
unsuitable
environment
for
UV-radiation
disinfection process.

25. UV radiation
 Dose Requirement is crucial in UV radiation
process. Required level of radiation dose to
disrupt and destroy microorganisms must be
maintained for the effectiveness.

26. UV radiation
 Radiation concentration, proper wavelength, exposure
time, water quality, flow rate, the micro-organism’s
type, source and its distance from the light source
determine the effective dose requirement.

27. Chlorination
 In Chlorination process, hypochlorous acid acts as
disinfecting agent. Hypochlorous acids are formed
when chlorine hydrolizes in water. When
hypochlorous acids splits into H+ and OCl- ions,
bacteria and viruses are inactivated and enzymatic
activities are inhibited.

28. Chlorination
 Chlorine has a higher degree of persistence in water
distribution systems.

29. Chlorination
 Chlorination can be applied in drinking water
operations such as treatment of ground
water,
industrial
process
water,
chilling
water, cooling tower systems, drip irrigation systems.

30. Chlorination
 In the chlorination process, chlorine has two forms in
water: free chlorine and combined chlorine. Sodium
hypochlorite or chlorine gas produces free chlorine
when added to water. When free chlorine and
ammonia reacts, combine chlorine is formed which
includes monochloramine and dichloramine.

31. Chlorination
 Gaseous
chlorine, chlorinated lime, sodium
hypochlorite and calcium hypochlorite are chlorinerelated compounds for water disinfection.

32. Chlorination
 Chlorine gas (Cl2) is highly toxic and liquefied under
pressure.
 Chlorinated lime (CaO2CaCl2O3H2O) is corrosive dry
white powder.

33. Chlorination
 Sodium
hypochlorite (NaClO) is corrosive and
yellowish liquid solution, commonly called “liquid
bleach” and calcium hypochlorite (Ca (ClO)24H2O) is
corrosive inflammable powder or granules and tablets.

34. Chlorination
 Sodium hypochlorite (NaClO) produces hypochlorous
acid (HClO) and hypochlorite (ClO-) ions, in water
which affects bacteria and viruses by inactivating and
inhibiting enzymatic activities.

35. Chlorination
 Sodium hypochlorite affects biological functions of
proteins and produces deleterious effects on DNA.