Correct Answer - Option 2 : Diameter of the particle intended to be removed
Concept:
The design overflow rate of sedimentation tank is the ratio of design discharge to surface area of tank. It is also called settling velocity of the concerned or intended size particle and settling velocity is given by:
\({V_s} = \;\frac{{\left( {{\rm{G}} - 1} \right){{\rm{d}}^2}}}{{18{\rm{\;\mu }}}}\)
Where,
G = specific gravity of intended size particle
d = intended particle size
If settling velocity of any particle is less than design overflow rate ( or settling velocity of intended size particle) will settle partially in sedimentation tank and particles whose settling velocity is more than or equal to design overflow rates will settle 100% or fully in sedimentation tank.
∴ Design overflow rate of sedimentation tank is chosen considering diameter of the particle intended to be removed.
Note:
1. Detention time decides the efficiency and size of the tank.
2. Flow rate through tank decides the size of tank or no. tanks required for treating raw water.
