Tennessee Wastewater Operator Practice Exam

What does large patches of white biofilm on an RBC indicate?

1. Excessive nutrients

2. Lack of oxygen

3. Increased BOD levels

4. Sufficient aeration

The correct answer is: Lack of oxygen

Large patches of white biofilm on a Rotating Biological Contactor (RBC) typically indicate a lack of oxygen. In RBC systems, biofilm formation occurs on the surfaces of the media, and when oxygen is limited, certain types of bacteria and microorganisms can proliferate unevenly, leading to the development of excessive biofilm. The white color often suggests the presence of specific aerobic microorganisms that thrive in less than optimal oxygen conditions. In the context of wastewater treatment, a healthy functioning RBC should have a balance of oxygen to maintain the necessary microbial activities for effective biological treatment. If oxygen levels decrease, it can lead to shifts in the microbial community structure, which might result in the formation of excessive biofilm, potentially causing operational issues such as clogging or reduction in treatment efficiency. The other choices relate to different environmental parameters within the wastewater treatment system. For instance, excessive nutrients could lead to biofilm growth but wouldn’t specifically result in a white color. Increased BOD levels likely signal higher organic matter presence rather than directly causing the observed effect. Sufficient aeration would promote a balanced and healthy biofilm rather than the irregular patches indicative of oxygen shortage.