Waste Water Engineering - Engineering

Q1:

The sewage discharge in a detritus tank of a treatment plant is 576 litres/sec with flow velocity of 0.2 m/sec. If the ratio of width to depth is 2, the depth is

A 100 cm

B 110 cm

C 120 cm

D 150 cm

ANS:C - 120 cm

To find the depth of the detritus tank, we can use the formula for the flow rate (Q) through a rectangular channel: Q=V×A Where:

  • Q is the flow rate (given as 576 liters/sec)
  • V is the flow velocity (given as 0.2 m/sec)
  • A is the cross-sectional area of the channel (which can be calculated from the dimensions of the channel)
The cross-sectional area (A) of a rectangular channel can be calculated as: A=Width×Depth Given that the ratio of width to depth is 2, we can express the width as twice the depth: Width=2×Depth Now, substituting the expressions for width and depth into the formula for area: 2A=(2×Depth)×Depth=2×Depth2 Now, let's substitute the given values into the flow rate formula: 576liters/sec=0.2m/sec×2×Depth2 576liters/sec=0.4m/sec×Depth2 Now, we can solve for the depth (Depth): Depth2=0.4m/sec576liters/sec​ Depth2=1440m2/sec Depth=1440​m Depth≈37.95m However, the depth is usually expressed in centimeters. So, converting meters to centimeters: ℎ≈37.95 m×100 cm/m  Depth≈3795cm Given the options provided, none of them match the calculated depth. It seems there might be an issue with the given parameters or calculations. Let's reconsider the problem.