Activated Sludge Process

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What is the reason for foaming in aeration tank and mlss turning to blackish color?

 

Taxonomy

11 Answers

  1. I completely concur and saved me doing a lot of writing.  This answer below is spot-on.  The only thing that I would add is a microscopic analysis of the sludge to tell you the predominance of different filamentous bacteria.  Then you can go to a decision tree to see what matches your situation (what you are doing wrong, i.e. O/G high, low DO, pH variations, temperatures, toxic or recalcitrant compounds, etc.)  The black as stated below is almost certainly septicity.  Increase your recycle rate first to get rid of the bottom portion of the clarifiers.  You may be running too high of bed levels, which give low DO environments and proliferate anaerobic bacteria which take oxygen from first nitrate and then sulfate in that order.)  There has to be float on the secondary clarifiers, unless you are running an MBR system.  Below is what I agree with whole-heartedly:

    Hi Arun,

    As people ​have already ​stated in ​the  ​comments, the ​foaming is ​normally caused ​by filamentous ​bacteria. There ​are conditions ​which create an ​ideal ​environment for ​the proliferation ​of these ​bacteria. Think ​of it like ​survival of the ​fittest, the ​filamentous ​bacteria are ​bigger than the ​other bacteria ​and will ​dominate in ​situations such ​as:

    Low F/M ratios.

    Low DO

    Insufficient nutrients.

    The black ​MLSS is ​normally a sign ​of septicity, ​once again low ​F/M, you will ​need to reduce ​sludge age ​ and WAS more ​frequently.​ 

     

    Thanks, Sean L. Roop - Senior Water and Wastewater Consultant - Industrial and Engineering Consultants, LLC.

  2. Hi Arun,

    As people have already stated in the  comments, the foaming is normally caused by filamentous bacteria. There are conditions which create an ideal environment for the proliferation of these bacteria. Think of it like survival of the fittest, the filamentous bacteria are bigger than the other bacteria and will dominate in situations such as:

    Low F/M ratios.

    Low DO

    Insufficient nutrients.

    The black MLSS is normally a sign of septicity, once again low F/M, you will need to reduce sludge age  and WAS more frequently. 

     

  3. Hi Arun.  I have come across this when the disinfecting chlorine somehow managed to get into the activated sludge bioreactor.  We were dosing the treated effluent stream with liquid chlorine and a leaking check valve allowed the chlorine to weep into the bioreactor.  It was a lesson never to be repeated.  At first we had no idea why the biomass was so black.  Aeration was good and at first we looked for a cause in the sewage.  This was in an SBR type treatment plant.

  6. Hi,

    your problem is very usual... it means that you can be at the presence of slowly biodegradable surfactants from industrial or municipal wastewater, proliferation of filamentous organisms in aeration tank or produced in anoxic zone of aeration tanks. What is the concentration of the oxygen in your aeration tank?

    regards

  7. Troubleshooting without details is difficult but from what you have described it sounds like a classic case of process turning septic, or anaerobic, that is typical colour, should also be offensive in smell?

    Cause? Well could be several from too low was rate to increase in solids load to power failure or reduced oxygen transfer rate, you should be measuring residual dissolved oxygen in the aerobic reactor and should be retained minimum 1.5mg/L

    the foaming then starts as the filamentous bacteria proliferate and dominate under these anaerobic conditions,

    not always easy to fix, I have a really good reference if you require

    regards

    gary 

  8. Hello it is simply a biological dysfunction. The organic matter in suspension is under the effect of putrefaction by a strong methanization of the medium. Any biomass that has become mud is no longer active and sees its destruction process triggered by putrefaction It is for this reason that WWTPs produce so many muddy residues of excrement. It's indestructible naturally out of the rotting function

  9. Bonjour il s'agit tout simplement d'un dysfonctionnement biologique. la matière organique en suspension est sous l'effet de la putréfaction par une forte méthanisation du milieu.

    Toute biomasse qui est devenue de la boue n'est plus active et voit son processus de destruction enclenché par la putréfaction

    C'est pour cette raison que les STEP produisent autant de résidus boueux d'excréments. C'est indestructible 

      

     

  10. Without having any information on the condition of the process preceding this observation, the my first thought would be that there was long interruption of oxygen supply. Would need additional process information to give a more specific answer.

    Regards

  11. Forming black color is because the active biomass is becoming inactive..an resulting in sludge. There are many reasons for the foam generation, narcotic microbes is one of them.