chlorination n chlorine demand

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.

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? 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 + NH 3 ↔ NH 2 Cl (monochloramine) + H 2 O HOCl + NH 2 Cl ↔ NHCl 2 (dichloramine) + H 2 O HOCl + NHCl 2 ↔ NCl 3 (trichloramine) + H 2 O 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.