Question

In the context of water and wastewater treatments, the correct statements are:

• A. particulate matter may shield microorganisms during disinfection
• B. ammonia decreases chlorine demand
• C. phosphorous stimulates algal and aquatic growth
• D. calcium and magnesium increase hardness and total dissolved solids

Hint:

Remember: - Ammonia increases chlorine demand.
- Phosphorus $\Rightarrow$ algal growth (eutrophication).
- Ca and Mg $\Rightarrow$ hardness + TDS.

Answer 1

The Correct Option is A, C, D

Statement (A): True. Particulate matter can shield microorganisms from exposure to disinfectants like chlorine or UV, reducing disinfection efficiency.
Statement (B): False. Ammonia actually increases chlorine demand because it reacts with chlorine to form chloramines (combined chlorine), thereby consuming more chlorine.
Statement (C): True. Phosphorus is a key nutrient for algae and aquatic plants. Excess phosphorus in water bodies leads to eutrophication, causing algal blooms and oxygen depletion.
Statement (D): True. Calcium and magnesium are the principal ions responsible for water hardness. They also contribute to total dissolved solids (TDS) in water.
Thus, the correct statements are (A), (C), and (D).
\[ \boxed{A,\ C,\ D} \]