Tennessee Wastewater Operator Practice Exam

If the MLSS has a Sludge Volume Index (SVI) greater than 200 ml/g, what condition is it defined as?

1. Normal

2. Clumping

3. Bulking

4. Flocculation

The correct answer is: Bulking

When the Mixed Liquor Suspended Solids (MLSS) has a Sludge Volume Index (SVI) greater than 200 ml/g, it indicates a condition known as bulking. Bulking occurs when the biomass in the wastewater treatment process forms aggregates that are too large or fluffy, preventing proper settling in the settling tanks. This poor settling can lead to increased solids in the treated effluent and operational challenges in the treatment plant. Bulking typically results from factors such as excessive growth of filamentous organisms or low dissolved oxygen levels, which can cause the microorganisms to clump together inefficiently. With an SVI over 200 ml/g, the sludge does not settle well, leading to operational issues such as reduced treatment efficiency and quality of the effluent. Monitoring SVI is essential for managing sludge settling characteristics in wastewater treatment processes. The other conditions, such as clumping and flocculation, refer to different behaviors of solids in the wastewater, but they do not imply the same degree of settling inefficiencies as bulking does, particularly at the SVI threshold noted.