Standard Article

Sedimentation and Flotation

Surface Water Hydrology

  1. Roger C. Viadero

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.sw866

Water Encyclopedia

Water Encyclopedia

How to Cite

Viadero, R. C. 2005. Sedimentation and Flotation. Water Encyclopedia. 3:404–408.

Author Information

  1. West Virginia University, Morgantown, West Virginia

Publication History

  1. Published Online: 15 JUL 2005


Waters and wastewaters typically contain particulate matter ranging from a few microns to centimeters in diameter, although the actual size distribution is often highly variable. One of the most common methods for the removal of particulate matter from waters and wastewaters is simple gravity settling, often referred to as “sedimentation.”

In water and wastewater treatment, four general classes of sedimentation can occur: Type 1, discrete settling; Type 2, flocculent settling; Type 3, hindered or “zone” settling; and Type 4, compression settling. In Type 1 settling, particles settle individually with no interparticle interactions. Consequently, no change in particle size occurs (i.e., floc formation). This system is often analyzed using Stokes' Law, based on a force balance on a single particle settling in a viscous medium under laminar flow conditions.


  • gravity settling;
  • sedimentation;
  • Stokes' law;
  • flocculent settling