A method commonly used to thicken activated sludge prior to treatment is:

The method commonly used to thicken activated sludge prior to treatment is dissolved air flotation. This process involves introducing air into the sludge mixture to create small air bubbles that attach to the solids. As the bubbles rise, they carry the solids with them to the surface, where they can be removed as a thickened layer of sludge. This method is effective because it allows for efficient separation of the solids from the liquid phase, which is crucial for preparing the sludge for further treatment or disposal.

Dissolved air flotation is preferred in many wastewater treatment facilities due to its ability to handle various types of sludge and its efficient operation. It is particularly useful in situations where the sludge has low density or when rapid thickening is required. This contrasts with other methods like gravity thickening, which relies on sedimentation and may not be as effective for all sludge characteristics, or composting and reed beds, which are more related to solid waste treatment rather than specifically thickening sludge before treatment.