GATE CE 2025 Set 1 — Question 31
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Environmental Engineering → Drinking Water Treatment → Sedimentation
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Question
The Surface Overflow Rate (SOR) in a rectangular sedimentation tank is . Minimum diameters of spherical inorganic and organic particles expected to be completely removed in this tank are calculated. Assume that Stoke’s law is applicable. Which of the following options is/are correct:Specific gravity of inorganic particles =
Specific gravity of organic particles =
Acceleration due to gravity () =
Kinematic viscosity () =
Specific gravity of organic particles =
Acceleration due to gravity () =
Kinematic viscosity () =
Correct answer
(A) Minimum diameter of inorganic particles is 24 μm; (B) Minimum diameter of organic particles is 69 μm
Solution
For a particle to be completely removed in a sedimentation tank, its settling velocity () must be greater than or equal to the Surface Overflow Rate (SOR).
Given: .
According to Stoke's Law:
Rearranging for diameter :
Thus, option (A) is correct.
Thus, option (B) is correct.
Given: .
According to Stoke's Law:
Rearranging for diameter :
1.For inorganic particles ():
.Thus, option (A) is correct.
2.For organic particles ():
.Thus, option (B) is correct.
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