Water purification involves removing undesirable contaminants through various treatment processes to produce water for specific purposes. The main steps include coagulation and flocculation to remove particles, sedimentation to allow solids to settle, filtration to remove smaller particles, aeration to remove gases, chemical treatment to adjust pH levels, and disinfection to kill pathogens using methods like chlorination. Chlorine is the most common disinfectant and works by forming hypochlorous acid which kills microorganisms. The effectiveness of disinfection depends on chlorine form, concentration, and contact time.

1. PURIFICATION OF WATER SUPPLIES
SUBMITTED BY : - SHIVANSU SURAJ
PIYUSH KUMAR
NANDAN MISHRA
PRATEEK ATAL
AKSHAY BADGUJAR
UNDER THE GUIDANCE OF
MS.YOGITA KUSHWAHA
MINOR PROJECT

2. • Water purification is the process of removing undesirable
chemicals, biological contaminants, suspended solids and
gases from water.
• The goal is to produce water for a specific purpose
WATER PURIFICATION

4. MAIN STEPS OF WATER PURIFICATION
• Coagulation and flocculation
• Sedimentation
• Filtration
• Aeration
• Chemical treatment
• Disinfection

5. COAGULATION AND FLOCCULATION
• Coagulation and flocculation are used to remove color,
turbidity, algae and other microorganisms from surface waters.
• The addition of a chemical coagulant to the water causes the
formation of a precipitate, or floc, which entraps these
impurities. Iron and aluminium can also be removed under
suitable conditions.
• The floc is separated from the treated water by
sedimentation and/or filtration, although flotation processes
may be used in place of sedimentation.

6. • The most commonly used coagulants are aluminium sulphate
and ferric sulphate.
• Coagulants are dosed in solution at a rate determined by raw
water quality near the inlet of a mixing tank or flocculator.
• The advantages of coagulation are that it reduces the time
required to settle out suspended solids and is very effective in
removing fine particles that are otherwise very difficult to
remove. Coagulation can also be effective in removing many
protozoa, bacteria and viruses.

8. SEDIMENTATION
• Simple sedimentation may be used to reduce turbidity and
solids in suspension.
• Sedimentation tanks are designed to reduce the velocity of
flow of water so as to permit suspended solids to settle
under gravity.

10. FILTRATION
Filters can also remove smaller particles like silt and suspended
solids; dissolved ions and some filters catch bacteria and viruses.
• There are many types of filtration method such as
i. screens,
ii. gravel filters,
iii. slow sand,
iv. rapid sand filters or cartridge filters.
 slow sand and rapid sand filters are mainly used

11. • Rapid sand filters filter water through sand, but speed up the
process by using chemicals as well.
• Slow sand filters however, use no chemicals or electricity to
function, but they are often large and require large areas.
• Slow sand filters consist of a layer of fine grain sand supported
on a layer of gravel, the topmost layer consisting of a biofilm
bacteria fungi and a range of aquatic larvae that have been
caught there.
• Sand filters require some time to mature, usually 10-20 days
before the filtered water is safe to drink.

13. AERATION
• Air stripping is used for removal of volatile organics (e.g.
solvents), carbon dioxide, disinfection by-products, some taste
and odor causing compounds.
• Aeration processes are designed to achieve efficient mass
transfer of oxygen into water and removal of gases and volatile
compounds by air stripping. Oxygen transfer can usually be
achieved using a diffusion of air into water, without the need for
elaborate equipment.

15. CHEMICAL TREATMENT
 ControlofpH
The pH value of water may need to be adjusted during treatment
and before distribution.
• to ensure that the pH value meets the water quality standards
• Where necessary, reduction of pH can be achieved by dosing with
a suitable acid such as sulphuric acid, hydrochloric acid, or carbon
dioxide.

16. • Many raw surface waters are slightly acidic and coagulation
processes further increase acidity. Increase of pH can be achieved
by:
•dosing with sodium hydroxide, calcium hydroxide or
sodium carbonate
•passage of the water through a bed of alkaline medium
•removal of excess carbon dioxide by aeration

17. DISINFECTION
• Contamination by sewage or animal faeces is the greatest danger
associated with water for drinking. This is because sewage from human
or animal sources may contain the causative organisms of many
communicable diseases.
• The use of disinfection to kill or inactivate pathogenic microorganisms is
necessary if the raw water contains organisms.
Ex: E. coli

18. • Several disinfection methods are used in water treatment.
–Disinfection with chlorine is the most widely used method for
large water supplies but its application is less common in small
supplies.
–Ultraviolet irradiation is the most common disinfection
method found in private supplies.

19. DISINFECTION WITH CHLORINE
• Chlorine, whether in the form of pure chlorine gas, sodium hypochlorite or
calcium hypochlorite, dissolves in water to form hypochlorous acid
(HOCl)
Cl2 + H2O ⇔ HOCl + HCl
• Hypochlorous acid is a weak acid which undergoes partial dissociation
to produce a hydrogen ion (H+) and a hypochlorite ion (OCl–):
HOCl ⇔ H+ + OCl–

20. • The total concentration of chlorine, hypochlorous acid and
hypochlorite ions is referred to as the free available chlorine.
• If ammonia is present in the raw water, the hypochlorous acid can
react to produce chloramines.
• Combined available chlorine is a less powerful disinfectant than
free available chlorine but gives a more persistent residual.
• NH3 ⇒ NH2Cl ⇒ NHCl2 ⇒ NHCl3

21. • The effectiveness of chlorine for disinfection depends on the
form of chlorine, its concentration and the contact time.
Hypochlorous acid is a more powerful disinfectant than the
hypochlorite ion and chlorination is usually practiced at values
of pH favorable to its formation.
• resulting in a free chlorine residual of 0.2 to 0.5mg/l”.