We have a problem with settlement in an aerator in a vegetable oil manufacturing company.
We have a conventional activated sludge process (ASP) treatment plant with 3 surface aerators of different capacity.
The ASP is designed so that the water from the primary clarifier goes to aerator 1, water from aerator 1 to aerator 2, and from aerator 2 to aerator 3.
The problem is that the settleability test shows the settlement of:
180 mg/l for aerator 1,
220 mg/l for aerator 2,
but the settlement for aerator 3 is increased and is 350 mg/l after 30 mins of the settleability test.
Following up on Colin: I think it's much simpler than the Mohlmann SVI stuff. They probably have 180, 220 and 350 ml settled MLSS per liter after 30 minutes of settling; Vaibhav please confirm or explain. If oxygen levels in A1 and A2 allow, here the sludge concentration should be increased through recirculation, which would result in a better performance and lower excess sludge production.
The problem is that the settleability test shows the settlement of:
180 mg/l for aerator 1,
220 mg/l for aerator 2,
but the settlement for aerator 3 is increased and is 350 mg/l after 30 mins of the settleability test.
How to reduce the settlement in aerator 3?
For a start I had to look up the Mohlman Index (Cheers Gerd) and found out Molman was the chap who devised the Sludge Volume Index. Who knew? Well not me until now. (Is this another Centigrade vs Celcius thing?)
I suspect the figures you are quoting - 180/220/350 are the Sludge Volume Index (SVI) or hopefully Stirred Sludge Volume Index (SSVI) and better still SSVI at 3.5g/l which allows for comparison of sludges at differing MLSS. The SVI and SSVI use the unit ml/g to show how much volume the sludge occupies after settlement. The higher the number, the poorer the sludge settles.
If we take the SSVI in reactor 3 it just doesn't sound good at 350, but the important part is are you losing solids from your clarifiers? You do have clarifiers?
If you are not losing solids then what is your real concern.
A cheap USB linked microscope (£50) linked to a PC - from Aldi or many other sources - would just about have sufficient magniofication to allow you to post some pictures of the flocc. Now that would bring you some responses.
I understand recent develoments using the NERADA process obviate such settlement base concerns. But hey, like we say oop North, we'll manage with what we've got. Presumably your plant worked fine at some point.
Like the others state, there is insufficient information to be able to advise you! If you would like to provide information such as do you have a DAF unit first? Is there an anoxic zone prior to the aeration zones? What is the MLSS level in each stage? What is the COD after each stage? But in a plant such as this, if it was in the UK, I would want to visit site and sample the bacteria, which I would examine, carry out oxygen levels on the plant and carry out various other tests?
Kindly send me your contact detail and factory detail on my mail ID: climateventure4careu@gmail.com and vimalesh.gci@gmail.com for visit of ETP, if you permit. Please share COD, BOD, Effluent feed flow in aeration Tank, Oil & grease level in aeration and raw effluent. Check the F/M ratio maintain it 0.25.
If you refer to the Mohlmann index, your biomass in "aerator 3" is just fine and you are not using the full capacity of A1 and A2. Have a look at the color and the shape of the sludge flocs. They should be reddish brown and distinct, with streaks of water in between.
Mariusz Wuss has already given the advice to increase the recirculation rate to increase (!) the MLSS concentration in the first two.
The appropriate solution can be suggested after knowing the quantity and quality of inlet water along with the solid loading under aeration. If a flow chart is available that will also help
Please provide flow rate in kld or m3/d, inlet characteristics and desired outlet characteristics to give us a general idea of the scale. You could possibly benefit from a system modifications or upgrade. Where are you located?
Are you reporting the Sludge Volume or the MLSS? The units seem to convey MLSS but the description as Settleability seems to convey a rough measurement of the Sludge Volume Index.Please clarify.
2. Please measure the MLSS at each stage also.
3. Additional details of Flow, Inlet BOD, COD, KW of each aerator, type of aerator and a sketch of the system would be helpful.