Thanks for your replies. I ...

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Thanks for your replies. I ...

Thanks for your replies. I ...

Thanks for your replies.

I checked by microscope sludge and foam yesterday, but surprisingly I didn’t find anything unusual as you can see in the photo. There were no filamentous, no M. Parvicella or Nocardia. I only saw that the sludge’s floc is little.

The sludge sedimentation is good and the SVI index is about 80-100, but the foam is growing little by little so we need constantly remove it.

Could the foam be the cause of industrial discharges, low temperature in the oxidation tank (12°C) or an incorrect airflow?

Thanks. Matteo

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If it's not filamentous, then either Surfactants, Nutrient imbalance, fines from an anarobic digester, or Toxicity.

What is the appearance of the foam?  Is it white or brown, stiff or billowy or slimy?  Surfactant foams are usually lighter color and billowy.  It's good to keep a couple of different defoamers on hand to try, to see what's effective for this. 

Nutrient imbalance is something to look at as well.  Do you calculate the C:N:P ratio on your Influent?  If the foam is slimy and you do an india ink test under the microscope you should be able to tell if polysaccharides are building up in the floc, which is an indicator for this.

Another possible cause of foam is toxicity, but your microscope photo looks OK.  Just to check though - are you seeing  Ammonia levels rise, or cloudiness in your Clarifiers/DAF ? 

 

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If foaming is serious, dosing anti-foam chemical is the fast way to control foaming.

you can check whether the foam is caused by surfactant discharged by industries. just take some influent and aerate, if you see foaming, then can we can confirm it is surfactant. if no foaming, then we can rule out the possibility.

if it is not caused by surfactant, then we can optimize the operation using methods suggested by other here, such as aeration, SRT, etc.

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