Wastewater New York State Practice Exam

What does a decrease in dissolved oxygen levels typically indicate in a wastewater treatment process?

1. Better nutrient cycling

2. Lower organic matter

3. Higher organic load

4. Enhanced treatment effectiveness

The correct answer is: Higher organic load

A decrease in dissolved oxygen levels during a wastewater treatment process typically indicates a higher organic load. When there is an increased amount of organic material present in the wastewater, microorganisms work to break this material down. This process consumes oxygen, and as more oxygen is depleted, the dissolved oxygen levels drop. In the context of wastewater treatment, dissolved oxygen is crucial for the survival and activity of aerobic microorganisms, which are responsible for decomposing organic pollutants. A significant drop in dissolved oxygen can signal that the demand for oxygen is exceeding its availability due to the presence of more organic waste than the system can efficiently manage. While lower organic matter, better nutrient cycling, or enhanced treatment effectiveness would generally correlate with stable or increasing levels of dissolved oxygen, a decrease indicates the opposite situation of struggling to process a higher than normal organic load. Thus, understanding the relationship between organic load and dissolved oxygen serves as a key indicator of the health and efficiency of the wastewater treatment process.