ANS:E - all the above.

The settlement of a particle in a sedimentation tank is influenced by various factors, including the velocity of flow, viscosity of water, size and shape of the solid particles, and the specific gravity of the solid particles. Let's delve into each of these factors and understand how they affect particle settlement:

1. Velocity of Flow: The velocity of flow in the sedimentation tank determines the rate at which water moves through the tank. Higher velocities can keep particles in suspension rather than allowing them to settle. If the flow velocity is too high, it can cause turbulence, which prevents settling by keeping particles in suspension. Conversely, lower velocities allow particles more time to settle out of the water.
2. Viscosity of Water: Viscosity refers to the resistance of a fluid to flow. Water viscosity influences the settling of particles because it affects the drag force acting on the particles as they settle through the water. Higher viscosity results in higher drag forces, which can slow down the settling process. Conversely, lower viscosity allows particles to settle more easily.
3. Size and Shape of Solid: The size and shape of solid particles significantly impact their settling behavior. Larger particles settle more quickly than smaller particles due to their greater mass and momentum. Additionally, the shape of particles can affect their settling characteristics. Irregularly shaped particles may experience more resistance as they settle compared to spherical particles of the same size and density.
4. Specific Gravity of Solid: Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water). The specific gravity of solid particles determines their buoyancy and settling behavior. Particles with a higher specific gravity settle more rapidly than those with a lower specific gravity because they are denser and experience greater gravitational forces pulling them downward.

In summary, the settlement of particles in a sedimentation tank is influenced by the velocity of flow, viscosity of water, size and shape of solid particles, and the specific gravity of the solid particles. These factors interact in complex ways to determine the settling rate of particles in the tank. Understanding these factors is crucial for optimizing the design and operation of sedimentation tanks in various industrial and environmental applications.