What does an SVI of 180 indicate in a settleometer?

An SVI, or Sludge Volume Index, of 180 indicates moderately aged sludge. The SVI is a measurement used in wastewater treatment to determine the settling characteristics of mixed liquor in a settling tank, typically expressed in milliliters per gram of suspended solids. An SVI value of around 180 suggests that the sludge is not overly fresh or new, which would typically have a lower SVI due to its higher density and lower volume. Conversely, a SVI above 180 often indicates increased levels of biological activity and possibly some degree of aging, which can affect the settling properties.

When sludge reaches this range, it typically indicates that it has undergone sufficient biological treatment but may not yet be at the point of being too degraded to perform efficiently in a settling process. This state can suggest that there is a balance between the solids being effectively compacted and the possibility of some settling issues if actions are not taken to manage the sludge properly. The nature of the sludge, whether it's aging or not, directly impacts its treatment efficiency and overall performance in the system.