What is indicated by an SVI greater than 150?

An SVI, or Sludge Volume Index, greater than 150 typically indicates a potential issue with the sludge characteristics in a wastewater treatment process, particularly bulking. When the SVI exceeds this threshold, it often means that the sludge has a lower density and is likely experiencing the beginning stages of bulking, where the biomass becomes less compact and does not settle well during the clarification phase. This can hinder the overall performance of treatment by causing floating sludge or scum on the surface.

A lower SVI value is generally associated with better clarification conditions, where sludge settles effectively, while higher values can signify problems. Therefore, an SVI above 150 serves as an important warning signal that operators need to monitor and address potential bulking issues in their treatment process to maintain optimal operation and ensure effective wastewater treatment.