Presence of vorticella or daphnia in activated sludge indicates what?

• A. Healthy
• B. Unhealthy
• C. Unstable
• D. Overactive

Answer: (A)

The presence of these organisms signals a healthy, functioning activated sludge system. Vorticella, a protozoan, and Daphnia, a zooplankton, thrive when there is a balanced food supply (bacteria) and adequate oxygen, indicating good aeration and a stable sludge age. Their presence shows the microbial community is mature enough to support higher life forms and that the treatment process is effectively converting organics and maintaining good settling characteristics. When the system is stressed or overloaded, these organisms tend to disappear, so seeing them is a positive indicator of health and stability.