The GATE Grind

GATE 2026 CE (CE1) – Question 25

Water and Waste Water Quality and Treatment · Primary, secondary and tertiary treatment, effluent standards · 1 mark · Multiple select

Which of the following components is/are NOT removed in the secondary treatment of sewage?

  1. Suspended settleable organic solids
  2. Colloids including dissolved organic matter
  3. Pathogens
  4. Fat and grease

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Show answer and explanation

Correct answer: (C) Pathogens; (D) Fat and grease

Explanation

Secondary biological treatment removes dissolved and colloidal organic matter and the remaining fine suspended organic solids. Fat and grease are mainly removed earlier in the primary treatment, and pathogens are only removed in small part and need disinfection. So C and D are not removed in the secondary treatment.