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1. Drinking water or Municipal water
Stages of
Treatment
Removal of suspended
contaminants
Disinfection:
Removal of
microorganism

2. Removal of suspended
contaminants
1. Screening
2. Sedimentation
3. Coagulation
4. Filtration

3. Screening
• Involves passing water
through screens with
large pores
• To remove floating
debris & large size
suspended particulates
like floating sticks and
twigs.

4. Sedimentation
1. Process in which water is at rest
in sedimentation tank to facilitate
gravity settling of suspended particles
2. Settled solids are removed
periodically
3. The rate of settling in still water at
100C is called hydraulic settling value of
particle.
4. Sedimentation is a slow and
incomplete process.

5. Coagulation
1. Coagulation involves the use of chemicals
which form ions on dissolving in water.
2. Alum, ferrous sulphate, aluminium
sulphate, potash alum, sod.aluminate.
3. Coagulants provide Al3+, Fe3+ ion which
neutralize negative charge on the colloidal
particles

7. Reactions
• Al 2(SO4)3 + Ca(HCO3)2  2Al(OH)3 + 3
CaSO4 + 6CO2
• NaAlO2 +2 H2O  Al(OH)3  + NaOH
• FeSO4 +Mg(HCO3)2  Fe(OH)2 +MgCO3
+ CO2 +H2O
• 4Fe(OH)2 +O2 +2 H2O 4 Fe(OH)3 

8. • Certain microorganism and colour
associated with the suspended matter also
get removed.
• Coagulant Aids: - Added to improve the
efficiency of coagulation process
1. Activated silica, fuller’s earth
2. Polyelectrolyte- polyacrylamide,
polyethylene, polydiallyldimethyl ammonium

9. Filtration
• Filtration aims at complete removal of
1. Suspended particles
2. Colloidal matter
3. Micro-organisms
The filter medium is usually a sand filter

10. Raw
Water
inlet
Raw
Water
Fine sand
Coarse sand
Fine gravel
Coarse gravel
Filtered
water

12. Disinfection
• Disinfection destroys pathogenic bacteria and is
essential to prevent the spread of
waterborne disease.
• By boiling water
• By chlorination: - A] Bleaching powder [CaOCl2]
B] By passing Cl gas /conc. chlorine solution
C] Using chloramine (NH2Cl).
Typically the final process in drinking-water
treatment, it is accomplished by ozone, or UV
radiation to clarified water.

13. Chlorination
Chlorination is the process of
adding chlorine to drinking water to
disinfect it and kill germs. Different
processes can be used to achieve safe
levels of chlorine in
drinking water. Chlorine is available as
compressed elemental gas, sodium
hypochlorite solution (NaOCl) or solid
calcium hypochlorite (Ca(OCl)2
The typical amount of chlorine gas
required for water treatment is 1-16
mg/L of water. Different amounts
of chlorine gas are used depending on
the quality of water that needs to be
treated

14. Sterilization by bleaching powder CaOCl2

15. Factor effecting
1. Time of contact
2. Temperature of water
3. pH value of water

16. By using chloramine(ClNH2)
• When chlorine and ammonia are mixed in
the ratio of 2:1 by volume , a compound
chloramine is formed
• Cl2 + NH3 → ClNH2 +HCl
• ClNH2 + H2O→ HOCl + NH4OH
• HOCl + germs germs are killed

17. Break point chlorination
• Break point chlorination is also known as
free residual chlorination. It involves the
addition of sufficient amount of chlorine to
oxidise (a) Organic matter (b) Reducing
substances (Fe2+, H2S etc.) (c) Free
ammonia in water; leaving behind mainly
free chlorine, which has disinfecting action
against disease causing bacteria.

18. • Breakpoint chlorination is the point where the demand
for chlorine has been fully satisfied in terms
of chlorine addition to the water. In other words,
the chlorine has completely reacted with the bather
pollutants leaving a zero chlorine residual. The addition
of chlorine to a water that contains ammonia or
nitrogen-containing organic matter produces an
increased combined chlorine residual.
• In wastewater treatment, breakpoint chlorination is a
means of eliminating ammonia, which is converted to an
oxidized volatile form. The addition of chlorine to a water
that contains ammonia or nitrogen-containing organic
matter produces an increased combined chlorine
residual.

21. Advantages
• All the organic compounds, pathogenic
(disease causing) bacteria and impurities
present in water are oxidised completely
with break point chlorination.
• The colour, taste and odour present in
water due to the microorganisms can be
removed by this process.
• It also prevents the growth of algae and
other organic matter.