PRIMARY/SECONDARY SEDIMENTATION

Sedimentation takes place in tanks that are round or rectangular basins, made of concrete or iron, with a bottom that slopes slightly toward an area where sludge is directed by means of special sludge collectors. Sedimentation can take place at various phases of the wastewater treatment process. Normally, sedimentation takes place first at the beginning of the treatment process to remove solids with screens and sand traps (primary sedimentation). After the biological stages of the process, sedimentation separates the activated sludge (secondary sedimentation). Finally, after the coagulation and flocculation stages, sedimentation is used to separate the precipitated chemical substances.
Source: Courtesy of Ambiente, an Eni Group Company