Tennessee Wastewater Operator Practice Exam

At which time is the pH typically lowest in an unaerated facultative pond?

1. Early morning

2. Midday

3. Late afternoon

4. Evening

The correct answer is: Early morning

In an unaerated facultative pond, the pH is typically lowest in the early morning due to the combination of biological activity and the absence of sunlight during the night. During the night, photosynthesis ceases, and respiration by microorganisms continues, which leads to the consumption of oxygen and the production of carbon dioxide. This carbon dioxide can combine with water to form carbonic acid, thereby lowering the pH of the pond. As sunlight begins to rise in the morning, photosynthesis starts to increase, which raises the pH throughout the day due to the uptake of carbon dioxide by aquatic plants and algae. This process typically results in a gradual increase in pH from morning to midday and onward. Hence, the early morning time frame is characterized by the lowest pH levels in an unaerated facultative pond, as biological processes dominate prior to the influence of sunlight.