Sludge Volume Index (SVI) is a parameter used in the operational maintenance of activated sludge treatment plants. It measures the settling characteristics of the sludge produced in the process. The SVI is calculated by dividing the volume of settled sludge by the volume of suspended solids after a specific settling period, typically 30 minutes. A lower SVI indicates better settling and compaction of the sludge. Monitoring SVI helps assess the performance of the treatment plant, optimize the waste sludge handling, and adjust the process parameters if needed. Regular measurement and control of SVI contribute to maintaining efficient sludge settling, reducing the risk of sludge carryover, and achieving stable treatment plant operation.