SV30 & SVI testing - what is high or low for your system

SV30 is among the simplest and most common of wastewater tests that we run. The SV30 reports the settled sludge (MLSS) volume after settling 30 minutes in a wide mouth graduated cylinder or dedicated settlometer.  The SVI calculation was designed to standardize the SV30 for different MLSS concentrations. For review:

SVI (ml/g) = SV30 (ml/L)                       
                     MLSS (g/L)                         
General SVI Guidelines

• ​< 80 - fast settling sludge, if supernatant is turbid low SVI indicates "old" sludge
• 100 - 200 - the range most activated sludge systems operate. Remember your secondary clarifier determines the upper limit for SVI.
• >250 - indicates severe bulking caused by filaments, non-filamentous bulking, or being extremely early on the growth curve.

So what ist he right SV30 & SVI for your system? Run the test at least daily. At the same time track effluent TSS, Return Sludge (RAS) concentration, and clarifier bed depths When all three tests/readings are in target range, you have your ideal SVI or SV30 (for a constant MLSS concentration).

Remember - the above ranges are just guidelines. Always refer to how well your secondary clarifier functions to get your system's true range for best SVI.