Answer:

Introduction:
Continuous flow water sedimentation tanks are used to remove suspended particles from water. These tanks work on the principle of gravity settling, where the particles settle down due to their weight. The settling velocity of particles plays a crucial role in the efficiency of the sedimentation process.

Explanation:
The settling velocity of particles refers to the speed at which particles settle down in a water sedimentation tank. It is influenced by various factors such as particle size, shape, density, and the characteristics of the water.

Surface Loading:
Surface loading in a sedimentation tank refers to the rate at which water flows into the tank per unit area of the tank's surface. It is typically expressed in terms of m^3/hr/m^2 or m/hr.

Relation between Settling Velocity and Surface Loading:
Particles with settling velocities greater than the surface loading of the tank are more likely to settle down efficiently. This is because they can overcome the upward flow of water and reach the bottom of the tank before being carried away.

On the other hand, particles with settling velocities less than the surface loading of the tank may not settle down properly. These particles may get entrained in the upward flow of water and remain suspended in the tank, reducing the efficiency of the sedimentation process.

Importance of Settling Velocity:
The settling velocity of particles determines the residence time required for particles to settle down in a sedimentation tank. If the settling velocity is too high, the particles may settle down too quickly, resulting in a short residence time and inadequate removal of particles. On the other hand, if the settling velocity is too low, the particles may not settle down within the desired residence time, leading to poor sedimentation efficiency.

Conclusion:
Particles intended to be removed in a continuous flow water sedimentation tank should have a settling velocity greater than the surface loading of the tank. This ensures that the particles can settle down efficiently and are not carried away by the upward flow of water. By maintaining the appropriate settling velocity, the sedimentation tank can effectively remove suspended particles and provide clean water.