Which factors significantly influence the gravitational settling (sedimentation) of a particle in a sedimentation tank handling sewage or water?

Introduction / Context:
Settling behavior in sedimentation tanks depends on properties of both the fluid and the particles. Designers must account for hydrodynamics and particle characteristics to predict removal efficiency.

Given Data / Assumptions:

• Parameters considered: tank velocity field, water viscosity, particle size/shape, particle specific gravity.

Concept / Approach:
Settling velocity depends on the net gravitational force minus buoyancy and drag. Drag depends on fluid viscosity and particle size/shape (which determines drag coefficient). The velocity field affects residence time and potential resuspension, thereby affecting overall removal.

Step-by-Step Solution:
Fluid property: viscosity influences drag and Reynolds number.Particle properties: size and shape affect projected area and drag coefficient; specific gravity affects net driving force.Hydraulics: velocity distribution controls detention time and short-circuiting.Therefore, all listed factors matter.

Verification / Alternative check:
Compare Stokes’ regime vs. transitional/newtonian regimes: each still depends on viscosity, size, and density contrast; tank hydraulics governs whether a particle can traverse the basin depth in the available time.

Why Other Options Are Wrong:

• Single-factor answers ignore the coupled nature of settling physics.

Common Pitfalls:
Assuming particle size alone dictates removal. In cold weather, higher viscosity can reduce settling velocity noticeably; poor hydraulics can also limit removal even for relatively heavy particles.

Final Answer:
All of the above (velocity field, viscosity, size/shape, and specific gravity).