Tennessee Wastewater Operator Practice Exam

What is a possible corrective action if a rotating biological contactor (RBC) turns white?

1. Pre-aerate wastewater influent

2. Add sodium nitrate or hydrogen peroxide in influent

3. Put another RBC unit online

4. Increase sludge retention time

The correct answer is: Pre-aerate wastewater influent

When a rotating biological contactor (RBC) turns white, it typically indicates an issue with the biological film attached to the rotating discs. This discoloration often suggests that the microbial population is suffering from stress, possibly due to insufficient oxygen levels or other adverse conditions. Pre-aerating the wastewater influent can enhance the oxygen levels in the incoming wastewater, which is crucial for the health of the microorganisms that form the biofilm on the RBC discs. Increased oxygen availability can promote the growth of beneficial bacteria, helping to restore the biological activity needed for effective treatment. Additionally, pre-aeration can assist in reducing odors and allowing for better degradation of organic materials before they reach the RBC system. The other options may not address the immediate need for improved oxygenation and microbial health, making pre-aeration a targeted approach to rectify the issue of the RBC turning white.