Tennessee Wastewater Operator Practice Exam

Why is nitrate sometimes added to the collection system?

1. To enhance biological growth

2. To control odors

3. To increase dissolved oxygen

4. To reduce ammonia levels

The correct answer is: To control odors

Nitrate is added to the collection system primarily to control odors. In wastewater management, particularly in collection systems where stagnant conditions may occur, the breakdown of organic matter can lead to the production of odorous compounds, including hydrogen sulfide. By introducing nitrate, it provides a source of nitrogen that enhances the activity of certain bacteria, which can lead to the conversion of these odorous compounds into less harmful and less odorous substances. This process not only helps mitigate unpleasant smells but also contributes to the overall improvement of water quality within the system. The other options represent important considerations in wastewater treatment, but they do not reflect the primary reason for adding nitrate to the collection system. Biological growth enhancement, increasing dissolved oxygen, and ammonia level reduction can be achieved through various treatments, but for odor control specifically, nitrate acts effectively by promoting specific microbial processes that outcompete those responsible for producing foul smells.