Tennessee Wastewater Operator Practice Exam

What SVI range indicates good settling quality of activated sludge?

1. 20-40

2. 50-100

3. 100-150

4. 150-200

The correct answer is: 50-100

The range of 50-100 for the Sludge Volume Index (SVI) indicates good settling quality of activated sludge. SVI is a measure of how easily activated sludge settles in a clarifier and is calculated by measuring the volume of settled sludge after a specific period and dividing it by the concentration of solids in the sample. An SVI value in this range suggests that the sludge has balanced characteristics suitable for effective sedimentation and separation from treated water. Values lower than this can indicate denser sludge that settles well, whereas values above this range can suggest poor settling, where the sludge may either become fluffy or scummy, leading to potential operational issues such as sludge bulking or floatation in clarifiers. Maintaining an SVI within this optimal range is crucial for efficient wastewater treatment and ensuring that the activated sludge system operates effectively.