The GATE Grind

GATE 2025 CE (CE1) – Question 21

Water and Waste Water Quality and Treatment · Water requirement, distribution system and drinking water treatment · 1 mark · Multiple choice

Fecal Coliform (FC) concentration in river water was measured as 10780 cfu/100 ml. The FC concentration after the conventional water treatment, but before chlorination, was measured as 23 cfu/100 ml. The 'Log Kill' (inactivation) of FC due to the conventional water treatment is closest to

  1. 4.00
  2. 2.50
  3. 2.67
  4. 3.00

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Correct answer: (C) 2.67

Explanation

Log kill is $\log_{10}\frac{N_0}{N} = \log_{10}\frac{10780}{23} = \log_{10} 468.7 = 2.67$.