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GATE 2021 CE (CE1) – Question 43

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

In a five-tube coliform test, sample volumes 0.01,0.001,0.0001 mL give positive counts 5,3,1. The supplied MPN table for 10,1,0.1 mL gives index 110 per 100 mL for 5–3–1 (other rows: 0–2–4→11,1–3–5→19,4–2–0→22). Find MPN per 100 mL.

  1. 1100000
  2. 110000
  3. 1100
  4. 110

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Show answer and explanation

Correct answer: (B) 110000

Explanation

The observed 5–3–1 pattern has tabulated index 110 for volumes 10,1,0.1 mL. Actual volumes are 1000 times smaller, so the organism concentration is 1000 times larger. Thus MPN is $110\times1000=\mathbf{110000}$ per 100 mL, **B**.