Texas Wastewater Class B Practice Exam

Denitrification in an activated sludge system occurs when there is insufficient what to maintain aerobic metabolism?

1. Dissolved Oxygen

2. Nitrogen

3. Carbon Dioxide

4. Hydrogen Sulfide

The correct answer is: Dissolved Oxygen

Denitrification in an activated sludge system primarily occurs in an anaerobic environment where there is a lack of dissolved oxygen. This process is crucial for the conversion of nitrate into nitrogen gas, which helps to reduce the nitrogen content in wastewater. In the absence of sufficient dissolved oxygen, specific bacteria engage in denitrification, using nitrate as an alternative electron acceptor during anaerobic respiration. The availability of dissolved oxygen is essential for aerobic metabolism, which is why its insufficiency triggers the conditions favorable for denitrification to take place. The other options do not directly relate to the critical requirement for denitrification in this context. Nitrogen (in the form of nitrate) is actually what is being consumed during denitrification. Carbon dioxide is a byproduct of aerobic respiration and is not a limiting factor in the denitrification process. Hydrogen sulfide is typically associated with anaerobic conditions but does not play a direct role in the denitrification process in activated sludge systems.