Question

Chloro-mines are used in water treatment for

• A. disinfection and control of taste and odour
• B. corrosion control
• C. removing turbidity
• D. control of bacteria

Hint:

Chloramines are widely used in water treatment because they are more stable than free chlorine, provide a long-lasting residual in the pipes, and minimize the formation of bad tastes, odors, and carcinogenic trihalomethanes (THMs).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the primary function of using chloramines (chloro-amines) as a treatment agent in municipal water purification systems.
Disinfection is the critical step in water treatment to destroy pathogens and make the water safe for human consumption.

Step 2: Key Formula or Approach:
Chloramines are formed by reacting chlorine with ammonia in water:
\[ \text{NH}_3 + \text{HOCl} \to \text{NH}_2\text{Cl} \text{ (monochloramine)} + \text{H}_2\text{O} \] Depending on the pH and chlorine-to-ammonia ratio, monochloramine (\(\text{NH}_2\text{Cl}\)), dichloramine (\(\text{NHCl}_2\)), and nitrogen trichloride (\(\text{NCl}_3\)) can be formed.
Monochloramine is the preferred form for water treatment.

Step 3: Detailed Explanation:
Let us compare chloramine disinfection with standard free chlorine chlorination:
- Disinfection: Chloramines are effective secondary disinfectants. Although they are slower-acting than free chlorine, they are highly stable and remain in the water distribution network for a much longer time, preventing bacterial regrowth (biofilms) in municipal pipelines.
- Taste and Odour Control: Free chlorine reacts with natural organic matter (such as decaying leaves and algae) present in raw water to form chlorinated organic compounds, which impart a strong, unpleasant medicinal taste and chemical odor to the water. In contrast, chloramines do not react as readily with organic matter, significantly reducing the formation of these odorous compounds and providing water with a better taste and less distinct chlorine smell.
- Reduced Disinfection Byproducts (DBPs): Using chloramines dramatically reduces the formation of regulated, carcinogenic DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) compared to free chlorine.
- Therefore, chloramines are chosen because they provide effective long-term disinfection while simultaneously controlling taste and odor issues.

Step 4: Final Answer
Thus, the correct option is (A).