Tennessee Wastewater Operator Practice Exam

What does an SVI of 300 indicate in a clarifier?

1. The solids are settling very rapidly

2. The solids are settling very slowly

3. The clarifier is overloaded

4. The effluent is clear

The correct answer is: The solids are settling very slowly

A Sludge Volume Index (SVI) of 300 indicates that the solids in the clarifier are settling very slowly. The SVI is a crucial parameter in wastewater treatment that assesses the settling characteristics of mixed liquor in the clarifier. A high SVI value, such as 300, suggests that the solids have poor settling ability and are likely to remain suspended in the water column longer than desired. In practice, a high SVI can lead to problems in the clarifier, including an increased risk of solids washout into the effluent, which can affect water quality and treatment efficiency. It may suggest issues such as the presence of excessive biological activity or filamentous organisms, which can hinder settling. Therefore, a value of 300 is a clear indication that solids are not settling effectively, making it critical for operators to monitor and adjust treatment processes to improve settling characteristics.