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GATE 2021 CE (CE1) – Question 38

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 2 marks · Multiple choice

A 50 mL wastewater sample is dried in a crucible. Empty crucible mass is 54.352 g; crucible plus dried sample is 55.129 g; after firing at 600°C for 1 h it is 54.783 g. Find total volatile solids concentration.

  1. 15540 mg/L
  2. 8620 mg/L
  3. 6920 mg/L
  4. 1700 mg/L

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Correct answer: (C) 6920 mg/L

Explanation

Volatile solids are the mass lost on ignition, not the whole dry residue. This loss is $55.129-54.783=0.346$ g=346 mg. Divide by 0.050 L to obtain **6920 mg/L (C)**. The empty crucible mass cancels in this difference.