Tennessee Wastewater Operator Practice Exam

What is the primary purpose of the primary clarifier in wastewater treatment?

1. Increase total suspended solids

2. Decrease BOD load to downstream processes

3. Improve nutrient removal efficiency

4. Enhance aeration efficiency

The correct answer is: Decrease BOD load to downstream processes

The primary purpose of the primary clarifier in wastewater treatment is to decrease the biochemical oxygen demand (BOD) load to downstream processes. The primary clarifier is designed to remove a significant portion of the suspended solids and organic matter from the raw wastewater before it is sent to the secondary treatment stages. By allowing the wastewater to settle, the primary clarifier reduces both the total suspended solids and the BOD, which is a measure of the organic matter present in the water that microorganisms would consume. Reducing the BOD load is crucial because it minimizes the strain on subsequent treatment processes, particularly aerobic treatment methods, where microorganisms break down the remaining organic matter. This not only enhances the overall efficiency of the wastewater treatment process but also helps in meeting regulatory effluent quality standards. Other options such as increasing total suspended solids, improving nutrient removal efficiency, or enhancing aeration efficiency are not primary functions of the clarifier. In fact, increasing total suspended solids contradicts its purpose, while the clarifier mainly focuses on solids and BOD removal rather than directly addressing nutrient removal or aeration.