Basic Wastewater Operator Practice Exam

What does the presence of amoebas, flagellates, and slow flow in the first set of discs indicate in an RBC plant?

1. Normal operation

2. Toxic waste entering the plant

3. Flow running too slow through discs

4. Flow running too fast

The correct answer is: Flow running too slow through discs

The indication that amoebas, flagellates, and slow flow are present in the first set of discs in a rotating biological contactor (RBC) plant points to flow dynamics that are not optimal for treatment processes. The presence of these microorganisms is often a sign that the environment in the RBC is conducive to their growth, which can occur when the hydraulic retention time is extended due to slow flow. This slow flow allows these organisms to thrive as they require a certain level of retention to survive and perform their biological functions. High numbers of amoebas and flagellates could imply that the biological treatment is responding to excess organic matter, suggesting that the system is not effectively managing the influent. In a well-operating RBC system, balanced velocity and appropriate microbial populations should be present; thus, reduced flow rates can hinder efficiency. Therefore, slow flow in the discs disrupts optimal treatment conditions by allowing for the undesirable proliferation of certain microorganisms, making this flow characteristic critical for proper analysis and adjustments in operations.