Chlorination is the process of adding chlorine to water to purify it for human consumption. Chlorine is effective at killing bacteria, viruses, and other pathogens. It has been widely used as a disinfectant since the early 1900s. When chlorine is added to water, it reacts with organic compounds and other substances, using up chlorine in the process. This usage of chlorine is known as chlorine demand. Understanding chlorine demand is important for properly designing chlorination processes to ensure water is sufficiently disinfected.

1. CHLORINATION
&
CHLORINE DEMAND
Ashwani Kumar
NMIT,Bengaluru

2. • Chlorination is the process of adding the element chlorine to water as a
method of water purification to make it fit for human consumption as
drinking water.
• WHAT IS CHLORINATION?
• Chlorine is the most widely used disinfectant.
As Chlorine compounds will destroy disease-causing organisms
quickly — usually after 30 minutes.
• Why do we chlorinate our water?
• A leading advantage of chlorination is that it has proven effective against
bacteria and viruses.
•The chlorination process is also fairly easy to implement, when compared
to other water treatment methods.
•It is an effective method in water emergency situations as it can eliminate
an overload of pathogens relatively quickly.

3. HISTORY OF CHLORINTION
Chlorine was first discovered in Sweden in 1744. At that time, people
believed that odours from the water were responsible for transmitting
diseases.
• In 1835, chlorine was used to remove odours from the water
• After 1890, chlorine became a way to reduce the amount of disease
transmitted through water.
• chlorination began in Great Britain and then expanded to the United
States in 1908 and Canada by 1917.

4. CHLORINATING WATER SUPPLIES
• The best practical method of chlorinating a supply of water is to use two
storage tanks of suitable size alternately, one
filled from the source, while the other is used for supply.

5. What Happens to Chlorine After it’s
Added to Water?
Cl2
Oxidizes organic acids
(making DPBs)
Reacts with organic nitrogen
(making Chloramines =
Combined Chlorine)
Oxidizes inorganics (e.g. Iron
and Manganese)
Free Chlorine
5
HOCl
OCl-

6. CHLORINATION MECHANICS
How well does chlorine work?
• Bacteria: Penetrates cell wall and kills the
organism.
• Viruses: Relatively effective inactivation.
• Giardia: Relatively ineffective inactivation.

7. Chlorine Treatment Standards: ‘C x T’
T = Time water is in contact with the chlorine
C = Concentration of free chlorine (mg/l),
measured after “T”
Need C x T = 6 for groundwater
0.3 mg/l for 20 min. same as 0.6 mg/l for 10 min.

8. CHLORINE CHEMISTRY
Total = Free chlorine + Combined chlorine
• Free chlorine:
hypochlorous acid + hypochlorite ion
HOCl ↔ H+ + OCl- [pH dependent reaction]
• Combined chlorine (chloramines):
• HOCl + NH3 ↔ NH2Cl (monochloramine) + H2O
• HOCl + NH2Cl ↔ NHCl2 (dichloramine) + H2O
• HOCl + NHCl2 ↔ NCl3 (trichloramine) + H2O
Chlorine combined with ammonia or organic nitrogen
(causes chlorine taste and odor)

9. 9
CHLORINE DEMAND
Chlorine Demand - Inherent properties
of the water that consume chlorine
• When chlorine is added to a water source, it purifies
the water by damaging the cell structure of bacterial
pollutants, thereby destroying them. The amount of
chlorine needed to do this is called the Chlorine
Demand of the water.

10. CHLORINE DEMAND
The remaining chlorine concentration after the chlorine demand is
accounted for is called total chlorine.
Total chlorine is further divided into:
•The amount of chlorine that has reacted with nitrates and is unavailable
for disinfection which is called combined chlorine .
• The free chlorine which is the chlorine available to inactivate disease-
causing organisms, and thus a measure to determine the potability of
water.

11. PROCESS FLOWCHART

12. CONCLUSIONS
• Chlorine demand has been shown to be a key parameter in
disinfection process design.
• Chlorine demand has been shown to be a very useful and
informative parameter in characterizing treated
surface water quality.
• The fulfilled objective in drinking water chlorine disinfection
process design is to ensure that the entire outflow from the
chlorine contact tank has been in contact with free chlorine at
a concentration and for a sufficient time period to
ensure compliance with the selected design value.