After a settleometer test, if you have a thin layer of clear supernatant over poorly settling sludge and your SVI is greater than 150 mL/g, this condition is referred to as ___________.

In this scenario, the description of having a thin layer of clear supernatant over poorly settling sludge, combined with a Sludge Volume Index (SVI) greater than 150 mL/g, indicates a condition known as sludge bulking. Sludge bulking occurs when the sludge does not settle properly, leading to an increase in the volume of settled sludge and a corresponding reduction in the clarity of the supernatant water above it.

The high SVI value further implies that the sludge is less dense and may have poor settling characteristics. This can be caused by various factors, such as the presence of filamentous bacteria that inhibit proper floc formation or by an imbalance of nutrients resulting in an unhealthy microbial population. In such cases, the sludge particles tend to have low agglomeration and can remain in suspension rather than settling at the bottom, hence the observable clear layer of liquid above.

Understanding this condition is crucial for wastewater treatment operators, as effective management strategies need to be implemented to address sludge bulking and restore efficient settling of solid waste. This can involve adjusting operational parameters, altering the inflow characteristics, or even chemical treatments to improve the flocculation of the sludge.