What type of treatment is mainly used to thicken sludge rather than dewater it?

The correct choice focuses on the Dissolved Air Flotation (DAF) process, which is specifically designed to enhance the thickening of sludge. DAF uses microbubbles to agitate and carry suspended solids to the surface, where they can be skimmed off. This process effectively concentrates sludge without performing extensive dewatering, as the primary goal is to reduce the volume of sludge through thickening, allowing for more efficient handling and processing in further stages of treatment.

In contrast, other methods such as filtration, activated sludge processes, and settling are oriented towards different outcomes. Filtration separates solids from liquids but does not primarily focus on thickening. The activated sludge process is used for biological treatment rather than thickening; it recycles activated sludge back to the aeration tanks to promote microbial digestion of organic matter. Settling, while it can contribute to the concentration of sludge, does not utilize air flotation techniques to enhance the process as effectively as DAF does. Therefore, the emphasis on sludge thickening distinguishes DAF as the most relevant method in this context.