Basic Wastewater Operator Practice Exam

Where is the highest concentration of algae growth usually observed in a facultative lagoon?

1. Near the top

2. Near the middle

3. At the bottom

4. At the effluent

The correct answer is: Near the top

In a facultative lagoon, the highest concentration of algae growth is typically observed near the top. This location provides optimal conditions for photosynthesis, as the upper layer of water is exposed to sunlight, which is essential for algae to thrive. The presence of sunlight promotes the growth of phytoplankton, which are microscopic plants that float in the water and use sunlight for energy. Additionally, the upper layer of the lagoon has more dissolved oxygen, which is produced by photosynthetic activity during the day. This oxygen is critical for aerobic microorganisms that help in the breakdown of organic materials. The combination of sunlight and oxygen availability creates a favorable environment for algae, making the surface layer the most productive area for algal growth in facultative lagoons. In contrast, the middle depths and the bottom of the lagoon typically have reduced light penetration and limited algae growth. The conditions in these areas may also favor different types of microorganisms or processes, but they do not support the high concentrations of algae found near the top. Lastly, the effluent area, although it may receive some nutrients from the lagoon, is not where algae density is maximized, as the water is usually clearer and may have less favorable conditions for algal proliferation compared to the upper layer.