Floating Sludge

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A plant recently experience shock loading event which resulted in the MLSS having settability issue.

 

The sludge is constantly floating ( scums formation) in the clarifier, causing sludge to overflow into the treated water channel.

Anyone has any idea what chain of events may cause the destabilisation of the mlss causing it to not settle?

Any recommendations for remedy?

The mlss has dropped 30% after the shock event and current sludge age looks young ( light brown colour with greyish tint).

Thank you all for any feedback

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7 Answers

  1. This has occurred because the plant has become overloaded and you have lost oxygen.  From the colour it sounds like it has become partially anaerobic and possible anoxic.  When plants lose oxygen, the organisms, which are able to grow at lower oxygen levels, or anoxically these grow more rapidly and don't become included in the main floc.  When the plant operates anoxically, the ultimate result is the conversion of Nitrate to Nitrogen gas and this causes the floc to separate.  If it is possible, increase the oxygen levels and add a high charge, high molecular weight cationic polymer to the aeration system.  This will help draw the sludge together.  The amount needed will depend on the size of your aeration system. The important thing is to get the aeration up and keep it up till the plant recovers.

    1 Comment

    1. To add on to Don's accurate assessment, remember when the sludge does not settle and massive surface accumulation occurs, you will lose some to carryover from the secondary clarifier, most likely why you have a drop in MLSS concentration. 

      Physical removal of accumulating surface scum or temporary high pressure jetting tends to speed up the recovery, by breaking the surface scum you will encourage re-settling that will be aided by the addition of the floc.

      In the event that filamentous bacteria tend to dominate colonisation, you may want to consider applying chlorine - be aware you run the risk of complete process failure if your chlorination is too high as you will destroy too many, or all of your biomass.

  3. Think Thomas is on the right track, this will be solved with the microscope, Settleometer and a thoughtful look at the clarifier.....or add some ferric and see if it works, keep an eye on pH.

  4. Organic shock loading can cause nitrogen deficiency if the ammonia is low.  The microbes can form exocellular polysaccharides  which make the MLSS settle poorly.  If the MLSS concentration has dropped this causes higher F/M ratio which can exacerbate the carbon/nitrogen imbalance.  Settleometer test will result in high sludge volume index.  Check influent data for BOD:N ratio being consistently higher than 100:1    This ratio may have gone low during the shock load.  To diagnose with microscope: 1) examine floc for indicators of nutrient deficiency such as 021N filaments or tetrads  2) perform india ink stain test on floc - polysaccharides do not accept stain and appear as white globs.   

  5. Hi, just a few questions to have a more accurate framing of the problem:

    1) is the sludge really floating on top of/above the water interface, or is it bulking sludge (most of the water column is occupied by slowly/not settling sludge, but with no sludge on top of the water interface).

    2) is there scum/foam formation in the aeration tank?

    3) does the influent contains in general substantial amounts of FOG, and was there a substantial higher FOG load during the shock-loading?

    4) is it an industrial or communal WWP, and in case of theformer, what is the type of industry connected?

    5) what are the normal, average Ntot and COD-concentration values in the influent? 

    6) how long is this foam:scum prblem ongoing? 

    7) Was there a microscopic sludge examination done on both the settleable fraction, asw ell as on the scum/foam fraction? If so, what were the results?

    1 Comment

  6. First floating sludge is most often caused by:

    • Denitrification  – small nitrogen gas bubbles float the sludge in the clarifier creating floating sludge chunks with small bubbles entrapped

    •   Fats, Oils & Grease  – simply put, FOG floats on water. When entrapped in floc, excessive grease or oil can cause floating biomass. This appears as a scum blanket that can cover the entire clarifier.

    • Viscous bulking  or billowing sludge – viscous bulking can sometimes create floating sludge (more often it is just billowing over the weir versus floating). This is often caused by nutrient deficiencies (normally low phosphate) in industrial waters.

    There are several ways to address the problem based on the cause. As suggested by Amit, bacteria growth can help or in some cases skimming of sludge will be helpful. 

    https://www.biologicalwasteexpert.com/blog/why-are-solids-are-floating-on-my-secondary-clarifier#:~:text=Denitrification%20%E2%80%93%20small%20nitrogen%20gas%20bubbles,put%2C%20FOG%20floats%20on%20water.&text=This%20is%20often%20caused%20by,low%20phosphate)%20in%20industrial%20waters.

  7. floating sludge is due to dead bacteria which didn't sustain the shock load and due to which the young bacterial growth in the bioreactor can be seen in the form of baby bacterial growth which are acclimatizing to the incoming effluent.

    this stage may take few days to stabilised the MLSS value. and offcourse the dead floating bacteria to be removed as it is just a "DEAD SLUDGE".

    regards.

    Technical Sales Engineer

    Amit S.

    Amalgam Biotech Pune

    +91 7447753382