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The Surface Overflow Rate (SOR) in a rectangular sedimentation tank is 45 m³/m²/d. Minimum diameters of spherical inorganic and organic particles expected to be completely removed in this tank are calculated. A sum that Stokes’s law is applicable. Specific gravity of inorganic particles = 2.65 Specific gravity of organic particles = 1.20 Acceleration due to gravity (g) = 9.81 m/s² Kinematic viscosity (ν) = 1 × 10⁻⁶ m²/s Which of the following options is/are correct:

1. Minimum diameter of inorganic particles is 24 μm
2. Minimum diameter of organic particles is 69 μm
3. Minimum diameter of inorganic particles is 15 μm
4. Minimum diameter of organic particles is 55 μm

Correct answer: Minimum diameter of inorganic particles is 24 μm

Solution

The correct option states that the minimum diameter of inorganic particles is 24 μm, which is derived from applying Stokes's law to the sedimentation conditions in the tank. This calculation takes into account the specific gravity of the particles, the kinematic viscosity of the fluid, and the surface overflow rate, leading to the conclusion that particles of this size can be effectively removed.

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