Tennessee Wastewater Operator Practice Exam

How does high dissolved oxygen affect the denitrification process?

1. It promotes denitrification

2. It has no effect

3. It inhibits denitrification

4. It speeds up the process

The correct answer is: It inhibits denitrification

High levels of dissolved oxygen negatively impact the denitrification process because denitrification is an anaerobic process, meaning it occurs in environments devoid of oxygen. During denitrification, bacteria convert nitrates (NO3-) into nitrogen gas (N2) or, to a lesser extent, nitrous oxide (N2O), facilitating the removal of nitrogen compounds from wastewater. The presence of high dissolved oxygen creates an aerobic environment, which favors the activity of organisms that utilize oxygen as their electron acceptor for respiration, rather than allowing denitrifying bacteria to thrive. In conditions where oxygen is plentiful, the denitrifying bacteria are less active or may even be outcompeted by aerobic bacteria, thus inhibiting the denitrification process. Therefore, maintaining lower levels of dissolved oxygen is crucial for effective denitrification, making the assertion that high dissolved oxygen inhibits this process correct.