GATE 2026 CE (CE1) – Question 65
The maximum demand at a water purification plant has been estimated as 12 million litres per day. For the raw supplies, a rectangular sedimentation tank is to be designed with mechanical sludge removal arrangement. Consider depth of the tank as 4 m, detention period as 6 hours, and velocity of flow as 0.003 m/s.
The width (in m) of the detention tank is ___________ (*rounded off to two decimal places*).
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Correct answer: 11.51 to 11.63
Explanation
The flow is $12 \times 10^6\ \text{L/day} = 12000$ m$^3$/day. The tank volume is $\frac{12000}{24} \times 6 = 3000$ m$^3$, so the plan area is $\frac{3000}{4} = 750$ m$^2$. The length from the velocity of flow is $L = vt = 0.003 \times 6 \times 3600 = 64.8$ m. The width is $\frac{750}{64.8} = 11.57$ m.