Tennessee Wastewater Operator Practice Exam

What is a likely effect on overall facility operations when one primary clarifier goes out for maintenance?

1. Decreased TSS and BOD loading

2. Increased BOD and TSS loading to secondary treatment

3. Improved effluent quality

4. Reduction in operational costs

The correct answer is: Increased BOD and TSS loading to secondary treatment

When one primary clarifier goes out for maintenance, the immediate consequence is a reduced capacity to separate solids from the wastewater before it enters the secondary treatment process. The primary clarifier's role is to remove settleable solids and a significant portion of biochemical oxygen demand (BOD) from the influent. With one clarifier offline, there will be an increased flow of Total Suspended Solids (TSS) and BOD entering the secondary treatment. This results from the remaining clarifier being unable to handle the entire incoming load, leading to a situation where more solids and organic matter reach the secondary treatment stage than the system is designed to manage efficiently. This imbalance can affect the operation and effectiveness of the secondary treatment processes, usually designed to handle a specific load based on full primary treatment capacity. Consequently, operators must closely monitor and potentially adjust their secondary treatment processes to maintain adequate removal efficiencies.