California Wastewater Treatment Operator Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice focuses on the Dissolved Air Flotation (DAF) process, which is primarily utilized for the thickening of sludge. In a DAF system, microscopic air bubbles are generated and introduced to the mixed liquor, causing the smaller solid particles and some of the suspended solids to rise to the surface, where they can be removed as a thickened sludge. This process effectively increases the concentration of solids, making it instrumental in thickening rather than explicitly dewatering.

In contrast, the activated sludge process primarily involves the treatment of wastewater and biological processes aimed at reducing the organic matter content. Trickling filtration uses a fixed film process where microbial growth on media treats the wastewater but does not focus on thickening sludge. Similarly, the Rotating Biological Contactor (RBC) employs a different biological treatment strategy that revolves around the rotation of media to provide surface area for biological growth, but it is not specifically designed for sludge thickening. Each of these alternatives serves a distinct function in wastewater treatment rather than the sludge thickening process that DAF is known for.