Tennessee Wastewater Operator Practice Exam

In an RBC system that employs co-settling, where are solids that settle into the secondary clarifier directed?

1. Back to the RBC

2. Sent to the primary clarifier

3. Discarded as waste

4. Moved to an anaerobic digester

The correct answer is: Sent to the primary clarifier

In a rotating biological contactor (RBC) system that uses co-settling, the solids that settle into the secondary clarifier are directed to the primary clarifier. This process is significant because the primary clarifier is where the initial settling of solids occurs prior to biological treatment. By directing the settled solids back to the primary clarifier, the system enhances the removal of suspended solids and any associated organic matter that may affect the overall efficiency of the treatment process. This practice can help in achieving better overall sedimentation and improve the quality of effluent by effectively managing the waste load. The other options, such as sending the solids back to the RBC, discarding them as waste, or moving them to an anaerobic digester, do not fit the operational purpose of the RBC system in a co-settling scenario. The RBC's role is primarily in biological treatment, while the primary clarifier is specifically designed for the settling and removal of solids prior to further treatment steps. Thus, the direction of settled solids back to the primary clarifier is a fundamental aspect of optimizing the treatment process in such systems.