Sedimentation

During sedimentation, particles with density greater than that of water accumulate at the bottom of the sedimentation tank, under the effect of gravity. These particles are periodically removed from the bottom of the sedimentation tank.

The clarified water, at the surface of the tank, is then sent to a filter. The settling velocity of a particle is proportional to its diameter and to its density.

In order to improve and accelerate the settling process, additives can be used in the pretreatment phase to aggregate and increase the weight of the particles in suspension.

Substances commonly used include powdered activated carbon, iron chloride or polychlorides of aluminum as well as a synthetic polymer that aggregates the floc.