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GATE 2017 CE (CE2) – Question 20

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

The most important species involved in organic-matter degradation in the activated-sludge process are ______.

  1. autotrophs
  2. heterotrophs
  3. prototrophs
  4. photoautotrophs

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Correct answer: (B) heterotrophs

Explanation

Heterotrophic microorganisms use organic carbon as substrate and oxidise organic matter while producing biomass. They therefore provide the principal carbonaceous treatment mechanism: **heterotrophs, B**. Autotrophic nitrifiers contribute nitrogen conversion but are not the main organisms for the stated organic-matter degradation.