What does the term "sludge volume index" (SVI) measure?

The term "sludge volume index" (SVI) refers specifically to a measure of the settleability of activated sludge in wastewater treatment processes. This index helps to determine how well the activated sludge settles during the clarification stage. It is defined as the volume of settled sludge (in milliliters) per unit of mixed liquor suspended solids (in grams) in a given sample after a specified settling time, typically 30 minutes.

A high SVI indicates poor settleability, which can lead to issues such as the sludge floating or not separating effectively from the treated water. Conversely, a low SVI suggests good settleability, which is desirable for effective treatment and clarification. Understanding the SVI is critical for operators to manage the activated sludge process effectively, as it can influence the removal of solids and the overall efficiency of the treatment plant.

In contrast, the other options relate to different aspects of wastewater treatment. The odor level, pH, and temperature variations are important parameters to monitor but are not directly linked to the SVI, which is solely focused on how well the sludge settles.