We often generate SV30 and SVI numbers in our monitoring - but rarely think about how to interpret the number. Remember the SV30 test is designed to predict secondary clarifier performance in suspended growth systems (normally activated sludge). While usually overlooked, I as operators questions about supernatant turbidity & fines remaining after the sludge settles. Additionally, does the sludge float after sitting for 2 hours due to denitrificiation? Another issue could be fats, oils, and grease causing a scum (floating sludge) layer on the top after 30 minutes.
For general guidance on how SVI relates to sludge settling characteristics:
SVI (ml/g) Sludge Settling & Compacting Characteristics
< 80 Excellent - but can leave "fines" if sludge age is too long
80 - 150 Normal zone - I usually suggest targeting 100 - 120 for best water
> 150 Poor settling - need to check for filaments or less likely viscous bulking
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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