Basic Wastewater Operator Practice Exam

What is the primary role of secondary clarifiers in wastewater treatment?

1. Disinfection

2. Nutrient removal

3. Sediment removal

4. Solids concentration

The correct answer is: Sediment removal

The primary role of secondary clarifiers in wastewater treatment is indeed focused on sediment removal. Secondary clarifiers are designed to separate and remove the biomass and other solids that have settled out after biological treatment processes, like activated sludge or trickling filters. During these processes, microorganisms break down organic materials, leading to an increase in suspended solids. Once this biological treatment has occurred, the secondary clarifier allows the mixed liquor to flow into the basin where gravity assists in settling the solids. The settled solids, often referred to as "sludge," are then typically recycled back into the treatment process or removed for further processing. This sedimentation process plays a crucial role in clarifying the effluent and minimizing the solids content, ensuring that the treated water that is discharged or further processed is of higher quality. It effectively reduces the turbidity and provides a clear effluent by allowing heavier particles to settle out. The other potential roles mentioned, such as disinfection or nutrient removal, involve different processes and equipment. While nutrient removal may occur in biological treatment stages or with other specialized equipment, the primary function of secondary clarifiers remains the effective settlement of solids.