Question

Make a review about Chlorine Disinfaction for water and its mechanism. Explain also the advantages as well as the disadvantages. (2 pages)

Answer 1

The main purpose for the addition of chlorine to the water is to destroy the bacteria contained in the water. Hence, chlorine is one of the disinfectants for water.

The mechanism for the chlorine disinfection of water:

The equations involved in the above mechanism are shown below.

HOCl H⁺ + OCl^-

Cl₂ + H₂O HOCl + H⁺ + Cl^-

H₂OCl⁺ HOCl + H⁺

2HOCl Cl₂O + H₂O

Cl₂ + Cl^- Cl₃^-

Chlorination:

Advantages:

1. Highly effective against bacterial and viral waterborne pathogens and some protozoa

2. Provides a residual level of disinfectant to help protect against microbial regrowth and to reduce biofilm growth in the distribution system

3. Easily applied, controlled, and monitored

4. Operationally simple and most reliable

5. The most cost-effective disinfectant

Disadvantages:

1. Disinfection byproduct formation (e.g., trihalomethanes, haloacetic acids, and other byproducts)

2. Will oxidize bromide in water to hypobromite forming brominated DBPs (Disinfection By-Products).

3. Not effective against Cryptosporidium

4. Requires transport and storage of chemicals

Elemental chlorine as a disinfectant:

Advantages:

1. The Least cost and the most energy-efficient of all chlorine-based disinfectants

2. Unlimited shelf-life

3. Does not add bromate

4. Will react with algal-produced microcystins

Disadvantages:

1. Hazardous pressurized gas requires special handling and operator training

2. Additional regulatory requirements, including EPA’s Risk Management Program and the Occupational Safety and Health Administration’s Process Safety Management Standard.