Basic Wastewater Operator Practice Exam

Which of the following is an indicator that the flow is running too slow in an RBC plant?

1. Amoebas and flagellates present

2. Increased clarity of effluent

3. Presence of rotifers and blood worms

4. A decrease in dissolved oxygen

The correct answer is: Amoebas and flagellates present

In a rotating biological contactor (RBC) system, the operational efficiency can be influenced significantly by the flow rate. The presence of amoebas and flagellates is indicative of a healthy microbial community, but also suggests specific conditions in the wastewater treatment process. When the flow in an RBC is too slow, it can lead to conditions that favor the growth of protozoa like amoebas and flagellates. These organisms thrive in environments where there is a stable, nutrient-rich substrate that does not rapidly wash away, which can occur with low flow rates. A slow flow rate can result in longer retention times in the treatment process, allowing for more microbial growth. If there are too many amoebas and flagellates, it often suggests an imbalance in the system, indicating that the flow is not optimal for effective treatment. In contrast, increased clarity in the effluent typically suggests effective settling and treatment processes, which would not align with the idea of flow being too slow. The presence of rotifers and blood worms might also be misinterpreted as a positive condition, but they usually thrive in different environmental conditions than optimal RBC operation. Lastly, a decrease in dissolved oxygen is often a result of stagnant conditions but does not specifically indicate