Tennessee Wastewater Operator Practice Exam

In unaerated aerobic and facultative ponds, the primary source of dissolved oxygen (DO) comes from?

1. Photosynthesis

2. Diffusion

3. Agitation

4. Microbial respiration

The correct answer is: Photosynthesis

The primary source of dissolved oxygen (DO) in unaerated aerobic and facultative ponds is photosynthesis. In these systems, aquatic plants and algae utilize sunlight to perform photosynthesis, converting carbon dioxide and water into glucose and oxygen. This process not only produces oxygen as a byproduct but also plays a significant role in maintaining the oxygen levels within the water, especially during daylight hours when sunlight is available. Photosynthesis is crucial in these environments because, unlike aerated systems, these ponds rely on natural processes rather than mechanical or artificial methods to infuse oxygen into the water. While diffusion does contribute to the overall oxygen levels by allowing oxygen from the atmosphere to enter the water, its contribution is relatively minimal compared to that provided by photosynthetic organisms in the pond. Agitation is not a significant contributor in unaerated systems, as the lack of artificial aeration devices minimizes the stirring of water that would help mix in oxygen. Microbial respiration utilizes oxygen rather than producing it, as microorganisms break down organic matter for energy, which can further decrease DO levels if not balanced by the oxygen produced through photosynthesis.