SLUDGE VOLUME INDEX (SVI)

A laboratory test result used to indicate the rate at which Sludge is to be returned from the discharge end of an Aeration Tank to the inflow (upstream) end. It is calculated as: SVI = (SV/MLSS) X 1,000; with the result in milligrams/gram and where SV is the sludge volume (solids settled in a 1-liter graduated cylinder after 30 minutes, in milliliters/liter) and MLSS is the level of Mixed Liquor Suspended Solids (MLSS), in milligrams/liter. The SVI has units of milliliters/gram. Used in conjunction with the Activated Sludge Process. Also known as the Mohlman Index.