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Waste Water Engineering - Engineering

Q1:

The settling velocity of the particles larger than 0.06 mm in a settling tank of depth 2.4 is 0.33 m per sec. The detention period recommended for the tank, is

A 30 minutes

B 1 hour

C 1 hour and 30 minutes

D 2 hours

E 3 hours.

ANS:D - 2 hours

Given:

  • Depth of tank (H) = 2.4 m
  • Settling velocity = 0.33 m/s
We use the formula: Detention period (hours) = Depth of tank (m) / Settling velocity (m/s) Substitute the given values: Detention period (hours) = 2.4 m / 0.33 m/s ≈ 7.27 hours However, in practice, detention periods are typically rounded to the nearest convenient time unit for operational ease. Therefore, considering the nearest option, 2 hours is insufficient for the settling tank in this case. The detention period of 2 hours would not provide enough time for the settling particles to effectively separate from the wastewater in the tank. A detention period of 2 hours may be appropriate for smaller settling tanks or under specific conditions where settling velocities are higher or particle sizes are smaller. However, in the given scenario with a settling velocity of 0.33 m/s and a tank depth of 2.4 meters, a detention period of 2 hours would likely lead to incomplete settling and reduced efficiency of the tank.