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GATE 2016 CE (CE1) – Question 28

Water and Waste Water Quality and Treatment · Sewerage system design and quantity of domestic wastewater · 1 mark · Multiple choice

Crown corrosion in a reinforced concrete sewer is caused by:

  1. H2S
  2. CO2
  3. CH4
  4. NH3

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Show answer and explanation

Correct answer: (A) H2S

Explanation

Anaerobic wastewater can release hydrogen sulphide into the sewer atmosphere. On moist surfaces above the water line, sulphur-oxidising bacteria convert it to sulphuric acid, which attacks concrete at the crown. This mechanism corresponds to **A**; the corrosion need not occur only on submerged surfaces.