What method is frequently used to thicken activated sludge before treatment?

The method frequently used to thicken activated sludge before treatment is dissolved air flotation. This process involves introducing air into the sludge, creating tiny bubbles that attach to the solids. As a result, the sludge becomes buoyant and rises to the surface, forming a thickened layer that can be easily removed. This method is particularly effective for the separation of particulates in low-density sludges, allowing for better management and preparation of sludge before further treatment processes.

Other methods, while they have their own applications, may not be as commonly used for thickening activated sludge specifically. Gravity settling relies on the natural settling of solids through a stationary column of liquid and may require longer retention times. Filtration typically focuses on separating solids from liquids using a filter medium, which may not be efficient for thickening. Centrifugation effectively separates components based on density by spinning them at high speeds, but it can be more energy-intensive and costly compared to dissolved air flotation.