GATE 2023 CE (CE2) – Question 48
In the context of water and wastewater treatments, the correct statements are:
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Correct answer: (A) particulate matter may shield microorganisms during disinfection; (C) phosphorous stimulates algal and aquatic growth; (D) calcium and magnesium increase hardness and total dissolved solids
Explanation
Check each statement in the water treatment context.
- **A. Particulate matter may shield microorganisms during disinfection.** True. Microbes inside or attached to particles are protected from the disinfectant, which is why turbidity must be removed first. ✓
- **B. Ammonia decreases chlorine demand.** False. Ammonia reacts with chlorine to make chloramines, so it **consumes** chlorine and **increases** the chlorine demand.
- **C. Phosphorus stimulates algal growth.** True. It is a limiting nutrient that causes eutrophication. ✓
- **D. Calcium and magnesium increase hardness and TDS.** True. They are the cations responsible for hardness and they add to dissolved solids. ✓
Correct: **A, C and D**.