Chlorination and De-chlorination

Chlorination and de-chlorination are essential processes in water treatment, particularly in municipal water supply and wastewater treatment. Here’s an overview of each process:

Chlorination

Purpose:

• Chlorination involves adding chlorine or chlorine compounds to water to disinfect it, killing or inactivating harmful microorganisms (bacteria, viruses, and protozoa). It also helps in controlling taste and odor and can oxidize certain contaminants.

Common Forms of Chlorine Used:

1. Sodium Hypochlorite (Bleach): A liquid form often used in drinking water treatment.
2. Calcium Hypochlorite: A solid form that is usually used in pool disinfection and in some water treatment plants.
3. Chlorine Gas: A highly effective but hazardous form used in larger water treatment facilities.

Process:

• Chlorine is added to water, typically in a controlled manner to achieve a specific residual concentration.
• The chlorine reacts with water to form hypochlorous acid (HOCl), which is the active disinfection agent.

Benefits:

• Effective disinfection and pathogen removal.
• Residual chlorine remains in the water, providing ongoing protection as it travels through the distribution system.

Considerations:

• Chlorination by-products: Can form when chlorine reacts with organic matter, leading to compounds such as trihalomethanes (THMs) and haloacetic acids (HAAs), which may be harmful in high concentrations.
• Taste and Odor: Some consumers may find chlorinated water has an undesirable taste or smell.

Dechlorination

Purpose:

• Dechlorination is the process of removing chlorine from water, typically before it is discharged into the environment or after it has served its purpose in the water supply.

Common Methods of Dechlorination:

1. Chemical Dechlorination:

1. • Sodium Bisulfite: A common reducing agent that reacts with chlorine to neutralize it.
   • Activated Carbon: Adsorbs residual chlorine effectively, often used in filtration systems.
   • Hydrogen Peroxide: Oxidizes chlorine, breaking it down into harmless by-products.

2. Physical Methods:

1. • Aeration: Allows chlorine to escape into the atmosphere. This method is less common due to its slower process and potential for loss of other gases.

Benefits:

• Protects aquatic life and ecosystems by ensuring that treated water does not harm the environment upon discharge.
• Improves water quality for further treatment processes or when used in irrigation or industrial applications.

Considerations:

• Proper Dosing: Adequate amounts of dechlorination agents must be used to ensure complete removal without excess chemicals remaining.
• Monitoring: Continuous monitoring of chlorine levels is essential to ensure effective dechlorination.

Summary

Chlorination and de-chlorination are critical in water treatment to ensure safe, clean water for consumption and environmental protection. Understanding both processes helps in designing effective water treatment systems that balance disinfection needs with the prevention of harmful by-products.