Wastewater Treatment Operator Certification Practice Test

What is the expected BOD removal efficiency in a facultative pond?

1. Mostly between 40 to 50%

2. Mostly between 30 to 40%

3. Mostly between 20 to 30%

4. Mostly between 70 to 80%

The correct answer is: Mostly between 70 to 80%

In a facultative pond, the expected biochemical oxygen demand (BOD) removal efficiency is often high, typically ranging from 70 to 80%. This high efficiency can be attributed to the specific biological processes that occur within these ponds. Facultative ponds are designed to promote both aerobic and anaerobic processes, depending on the depth of the water and the availability of sunlight. In the upper aerobic layer, algae produce oxygen through photosynthesis, which supports the breakdown of organic matter by aerobic bacteria. This process effectively reduces the BOD of the wastewater. The anaerobic conditions that may exist in the deeper layers also contribute to the digestion of waste, albeit at a slower rate. The combination of both aerobic and anaerobic treatment processes allows facultative ponds to achieve significant BOD reduction, making them effective in treating wastewater while being relatively low in operational requirements. In contrast, lower removal efficiencies mentioned in the other options would indicate either shallower or less well-functioning systems, which do not harness the full potential of the biological activity present in a facultative pond.