What can an increase in Sludge Volume Index (SVI) indicate?

An increase in Sludge Volume Index (SVI) indicates a tendency toward sludge bulking. SVI is a critical measure used in wastewater treatment processes, primarily to assess the settling characteristics of activated sludge. It is defined as the volume of settled sludge (in mL) per gram of suspended solids after a specified time.

When SVI increases, it often signifies that the sludge is less dense and more prone to bulking, which can cause operational challenges such as poor settling and increased suspended solids in the effluent. This bulking phenomenon occurs when certain microorganisms, particularly filamentous bacteria, grow excessively, creating a network that traps water and prevents the proper settling of sludge.

Recognizing an increase in SVI is essential for operators, as it may indicate that adjustments are needed in the treatment process to ensure efficient separation of solids from liquids and to maintain overall treatment effectiveness.