If the activated sludge in your plant has no vorticella or daphnia, this indicates a ____ process.

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

Answer: (B)

In activated sludge, the makeup of the microbial community serves as a live indicator of how the process is performing. Vorticella, a common protozoan, and Daphnia, a filter-feeding crustacean, are typical inhabitants of a balanced, mature mixed liquor. They help keep the bacterial population in check and support good floc formation and settling.

If you don’t see these organisms, it suggests the environment isn’t supporting a healthy, stable community. That usually means the process is under stress or unfavorable conditions are present, which can lead to poor sludge settling, potential bulking, and overall reduced treatment efficiency. Causes could include toxic shocks, improper aeration, problematic chemical residuals, or other disturbances that suppress protozoa and larger grazers. So this observation points to an unhealthy process.