I am monitoring an aeration tank tank with a volume of 1900 m3 having MLSS concentration around 3000 to 4000 mg/l. The SV30 is about 70%, previously in winter it was around 40%. I cannot bring MLSS concentration below 3000 mg/l as it affects the degradation performance. The DO level is maintained around 1 to 3 mg/l. Do I have any other option except wasting sludge?
Shan Saleem
Obviously you've got light sludge. At say 3.5 g/l MLSS and 700 ml/l SV30, the SVI = 700 / 3.5 = 200 ml/g. As to decrease the SV30 at sufficiently high MLSS and SRT, this SVI needs to be drastically lower.
I assume that you operate a conventional activated sludge (CAS) system consisting of just an aeration tank and a clarifier with sludge recycle/waste (RAS/WAS). In that case, there is very little that you can do to lower the SVI aside from balancing your macro-nutrients (nitrogen, phosphorus) versus the organic load BOD:N:P = 100:5:1 . The proven first upgrade to get much lower SVI would be to insert at least a well mixed anoxic (no aeration) selector/contact tank/compartment at the inlet of the aeration tank as to contact the influent directly with the RAS. A further upgrade would be to insert a regeneration tank on the RAS upstream of the selector/contact tank. In this way, we achieve SVI < 30 ml/g and much better effluent quality (ultralow BOD, COD, turbidity, ...) for sustainable water reuse.
Maintain DO around 1.5 ppm by reducing aeration. Check the SVI, ideal value 100-150. If you have a Secondary Clarifier and sludge is floating, then you need to waste the settled sludge
The high SVI (as calculated by Bruno) is very likely caused by filamentous microorganisms. If you have access to a good microscope, you may be able to identify the type of filaments, and this may then tell you the cause of the excessive filamentous growth, e.g., low organic loading (F/M), low dissolved oxygen, low nitrogen, low pH. The filament identification was developed by Dick Eikelboom in the Netherlands. A paper describing the method is Strom and Jenkins, 1984 (attached). Jenkins, Richard, & Daigger have an excellent Manual. Good luck!
- Peter
I can suggest one non-theoratical self-developed tactic that would definitely help you. I did this procedure as an action plan to recover SRT imbalance during my tenure as Process Engineer for 15 MLD Tannery wastewater treatment plant in India. There were 07 aeration compartments, I purposely switched-off aeration in two compartments (6th and 7th) for 48 hours and recycle almost entire the activated sludge from these two compartments to 1st compartment. In this way, we found tremendously quick growth and improved settling of the sludge after three days of the operation. The acquired also performed better for the efficient exhaustion Of nocardia/scum over liquid surface. Although, you would get higher TSS in the treated effluent for 2-4 days but, later, it comes to the original position. The excess TSS in the clarifier can be easily manage by spray 20 L prepared sutiin thrice in a day basis of non-ionic flocculent (dissolve 1Kg/60L tap water). Please note that, it is just a quick recovery procedure in case you are in trouble with complying discharge norms.
Other practical methods are,
1. Add DAP/external carbon dose regularly.
2. Do shock loading of the feed, in this case more substrate will be available for the microbiota that would trigger microbial growth.
3. Check MPN and do accordingly as per suggested.
4. Maintain SRT in system.
5. Maintain lower DO operation. This would promote filamentous/facultative growth in the system.
Shan Saleem
Please do visit this link for troubleshooting and there are many more available as well online
https://www.processingmagazine.com/home/article/15583654/control-of-activated-sludge-including-troubleshooting
hope so this is in line with your requirement and would love to help you out with some more links if this doesn't solve your purpose
stay connected and am sure we can do something jointly if you are intrested
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