Wastewater Treatment Operator Certification Practice Test

What is the typical removal efficiency from bacteria in a primary clarifier?

1. 0-5%

2. 25-75%

3. 5-10%

4. 10-20%

The correct answer is: 25-75%

The typical removal efficiency of bacteria in a primary clarifier is usually around 25-75%. This range is significant because primary clarifiers are critical components in the wastewater treatment process, designed primarily for the physical separation of solids from liquid waste. The primary clarifier allows for the settling of suspended solids, which also captures some bacteria present in wastewater during this process. The clarification process, while not solely focused on bacterial removal, does result in a considerable amount of bacteria being trapped in the sludge that settles to the bottom of the clarifier. This happens because a portion of the bacteria adheres to the larger particles of organic and inorganic materials that are settling. Thus, during primary treatment, while the focus is on solids removal, there is an incidental reduction of bacteria, leading to the efficient removal range stated. In contrast, other options suggest lower efficiency percentages that do not accurately reflect the clarifier's ability to reduce bacterial content in typical applications. Therefore, the assessment of bacterial removal being around 25-75% aligns well with the operational performance characteristics seen in primary clarifiers.