SV30 - going beyond the 30 min sludge level number to give valuable information

The SV30 is possibly the easiest test done by wastewater treatment system operators. Fill a wide cylinder or settleometer with aeration basin MLSS and allow to settle for 30 minutes. This test is designed to give you settling rates for the MLSS and an estimate of how well secondary clarification will work. If all things are in good shape, just reading the 30 minute number is enough. However if you have problems with filamentous or non-filamentous bulking, secondary clarifiers have become undersized (either by hydraulic or solids carrying rate), denitrification, or have problems with pin-floc, fines, or turbidity - you should do more than just read the number after 30 minutes. Here is how to take advantage of settling tests using SV30 equipment.

• Monitor settling rate every 5 minutes during the SV30 test. You want the MLSS to settle but not too fast. Old sludge rapidly drops, but leaves turbidity and pin floc in the supernatant. Younger sludge settles more slowly, yet captures more of the small solids that contribute to pin floc or turbidity.
• Don't dump the sample after 30 minutes. Allow to settle for several hours and monitor compaction (secondary clarifiers run in the hours not minutes. If after time you see floating sludge and small bubbles, you can have denitrification. If a secondary clarifier is denitrifying, you can find the maximum solids inventory time before you start to see problems.
• If the MLSS does not compact well, you can confirm filaments or non-filamentous bulking with a microscopic exam. The amount of compaction can be correlated to what you see under the microscope which is less subjective that other filament abundance estimate methods.
• Rapid deflocculation - mainly an industrial WW phenomenon - spills happen in industrial WW. The first sign of problems is an increase in turbidity, free-bacteria in solution, and floating solids. The SV30 test can help detect spills - just look at supernatant turbidity and floating solids.
• Filamentous bulking often makes a rough layer on top of the MLSS line in the SV30 test. If you have rough MLSS with a steel-wool or mesh appearance, you have filamentous organisms extending from the floc.
• MLSS color - color helps indicate sludge age and microbial makeup. Note the MLSS color!

Above are the most common SV30 test extensions that I use. Do you have any other observations that relate to effluent quality or clarifier performance? If so, please comment.