Texas Wastewater Class B Practice Exam

What pollutant in the effluent from the activated sludge process may create toxic conditions for aquatic life?

1. Phosphorus

2. Nitrogen

3. Carbon

4. Sulfur

The correct answer is: Nitrogen

Nitrogen, when present in effluent from the activated sludge process, can lead to toxic conditions for aquatic life primarily through its compounds, such as ammonia and nitrates. Ammonia is particularly harmful because at elevated concentrations it is toxic to fish and other aquatic organisms. It can disrupt the normal functioning of fish gills, inhibit their ability to take up oxygen, and impair their overall health. Additionally, when nitrogen is converted to nitrate during the nitrification process, it can contribute to issues such as eutrophication in water bodies. Eutrophication can lead to algal blooms, which upon decaying consume oxygen and create hypoxic conditions, further stressing or eliminating aquatic life. Therefore, nitrogen’s involvement in both acute toxicity and long-term ecological impacts makes it a significant pollutant in wastewater effluent, especially in terms of the health of aquatic ecosystems.