Tennessee Wastewater Operator Practice Exam

Primary clarifiers are primarily designed to remove what type of solids?

1. Suspended solids

2. Settleable solids

3. Colloidal solids

4. Dissolved solids

The correct answer is: Settleable solids

Primary clarifiers are primarily designed to remove settleable solids from wastewater. These solids are typically larger particles that can settle to the bottom of the clarifier due to gravity during the sedimentation process. The design of primary clarifiers includes the use of a large tank volume and gentle flow conditions, allowing particles heavy enough to settle to do so, thereby separating them from the liquid phase. Settling occurs based on the principle that heavier particles will naturally move downward when the water is quiescent. This sedimentation process effectively reduces the load of solids that would otherwise enter secondary treatment processes, improving overall treatment efficiency. In contrast, suspended solids that do not settle and colloidal solids, which remain dispersed in the liquid without settling, are not effectively removed in primary clarification. Dissolved solids are even smaller and remain in solution, making them beyond the scope of what primary clarifiers can address. Understanding this, the primary function of a primary clarifier is to enhance the treatment process by targeting those settleable solids, making it crucial in the overall wastewater management system.