Tennessee Wastewater Operator Practice Exam

If the appearance of a rotating biological contactor (RBC) becomes white, what is the likely cause?

1. A lack of nutrients

2. Overabundance of fats

3. A type of bacteria feeding on sulfur compounds

4. Excessive organic loads

The correct answer is: A type of bacteria feeding on sulfur compounds

The appearance of a rotating biological contactor (RBC) turning white can indeed indicate the presence of a certain type of bacteria that are thriving in the system. When RBCs are experiencing this change in coloration, it is often attributed to the growth of sulfur-oxidizing bacteria. These bacteria can leverage sulfur compounds from the wastewater, leading to a relatively high population density that can alter the visual characteristics of the RBC media. Typically, the appearance of white could suggest a healthy biofilm, but if it becomes overly pronounced, it signals a potential imbalance or specific metabolic activity related to sulfur metabolism. This condition may highlight the system's ability to process or remove sulfur compounds effectively. In contrast, other causes, like a lack of nutrients or excessive organic loads, would typically manifest in different ways, such as poor biological activity or sludge formation rather than a uniform white appearance across the media.