California Wastewater Treatment Operator Practice Exam

Which process is primarily used in primary wastewater treatment?

1. Filtration

2. Pumping

3. Sedimentation

4. Centrifugation

The correct answer is: Sedimentation

The process primarily used in primary wastewater treatment is sedimentation. During this stage of treatment, wastewater is allowed to sit in a large tank, often referred to as a primary clarifier or sedimentation basin. This process is designed to remove larger solids and particulate matter from the wastewater by allowing gravity to pull these heavier materials to the bottom of the tank, where they form a sludge layer. Sedimentation effectively separates the solid materials from the liquid phase. The clarified liquid, which is free from a significant amount of suspended solids, then moves on to secondary treatment stages. This step is crucial as it reduces the organic load and the amount of total suspended solids entering the subsequent treatment processes, thus improving the overall efficiency of the wastewater treatment system. Other processes such as filtration, pumping, and centrifugation do not serve the same primary function in the initial treatment phase. Filtration is more commonly associated with secondary or tertiary treatments where finer particles are removed. Pumping is a supportive action in the transportation of wastewater but does not specifically treat the water. Centrifugation, while effective for separating components based on density, is usually not applied at the primary treatment stage in standard wastewater treatment practices.