GATE 2022 CE (CE1) – Question 61
A water treatment plant has a sedimentation basin of depth 3 m, width 5 m, and length 40 m. The water inflow rate is 500 m3/h. The removal fraction of particles having a settling velocity of 1.0 m/h is_______. (round off to one decimal place) (Consider the particle density as 2650 kg/m3 and liquid density as 991 kg/m3)
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Correct answer: 0.39 to 0.41
Explanation
The surface overflow rate is $Q/A=500/(5\times40)=2.5$ m/h. For ideal discrete settling with particle velocity below overflow rate, the removal fraction is $v_s/v_o$.
Therefore removal = $1/2.5=\mathbf{0.4}$. Basin depth and particle densities are unnecessary because settling velocity is already supplied.