Massachusetts Wastewater Practice Exam

Which is a common cause of odor in wastewater treatment plants?

1. Presence of ammonia.

2. Excessive nutrients.

3. High temperatures.

4. Low dissolved oxygen levels.

The correct answer is: Low dissolved oxygen levels.

A common cause of odor in wastewater treatment plants is the presence of low dissolved oxygen levels. When the oxygen concentration in the treatment process drops significantly, anaerobic conditions can develop. Under these anaerobic conditions, bacteria that thrive without oxygen begin to dominate. These bacteria can produce foul-smelling compounds as they break down organic matter. The release of gases such as hydrogen sulfide, methane, and others contributes significantly to the unpleasant odors associated with wastewater facilities. Maintaining adequate dissolved oxygen levels is crucial not only for odor control but also for ensuring the effectiveness of the biological treatment processes. The other options can contribute to various issues within the treatment plant, but low dissolved oxygen levels are particularly significant for odor generation. For instance, while ammonia can create odors, it typically does so in conjunction with other factors and is less of an independent odor source compared to the effects of anaerobic conditions. Excessive nutrients often lead to problems like algal blooms rather than direct odors, and high temperatures can accelerate biological processes but are not specifically tied to odor production as much as the absence of dissolved oxygen.