How to get rid of scum?

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We are facing the  problem of reducing the scum which is developed  in our secondary settling tanks in aeration process. 

How can  the formation of this foamy scum be minimised? Which chemicals should be used for dosing?  

Please share your experiences and advice.  

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10 Answers

  1. let the mixture rest for sometime and then pour it with a scupper slightly dipping and there by blocking the scum; then you need to remove the scum from the scupper with some laterally sliding equipement.

    LMAJdS 

  2. Dear Zyaad,

    Foaming in activated sludge process is a common operational problem in many wastewater treatment plants.The foam can occur in aeration tank, Followings process to remove scum.

    1. Verify that the return sludge is flowing to the aeration tank. Maintain a sufficient return sludge

    rate to keep secondary clarifier blanket to normal levels (1ft to 3 ft).

    2.  Stop wasting activated sludge for a short time to build the MLSS levels back up and MCRT to

    desired range.

    3.  Control air flow rates to control DO in the 1.0 to 3.0 mg/l range. Foaming may persist longer

    with fine bubble aeration compared to course bubble aeration.

    –4. Consider hauling in seed activated sludge if warranted

    –5.Actively enforce sewer use ordinances to avoid process upset and deterioration of the

    secondary system. Check out the distribution of return sludge, and influent into the basin for

    proper flow split.If nitrification is not required, gradually increase the F/M and decrease the MCRT.

    6.If the scum is not returned to the aeration tanks, include the volatile solids removed in

    the scum in the waste sludge calculations. During normal operation, the amount of

    volatile solids removed with the scum is to small to matter. However during periods of

    high foam, 10 to 15% of the solids may be removed with the scum.

    7. If filaments appear, try to identify the cause. There are several books on the market

    that will help you identify the type of filament and how to control it. A microscope is a

    must in identification of filaments.

  3. Dear Zayed - when I was with DM in the Waste Treatment Section we were trying to develop the SOPs based upon RCA , FMEA and the data analytics. we developed a number of draft guidelines _ Do you have to these ?

  4. Dear 

    Check the color of scum, there are many reasons , check the ski,  do set,  quick solution is spreading water peroxide how. 

    Eyad

  5. Try to avoid recirculation of the scum. Try to discharge the scum separately. If scum is due to Microthrix Parvicella polyaluminum chloride dosage (few mg/l) may help. Alternatively sprinkle a diluted solution of sodium hypochlorite on the surface of the settling tank. In this case pay attention to clogging of sprinkling nozzles due to carbonate precipitation. To avoid it, provide dropping NaHClO on a jet of tap water at the sprinkling point. This technique proved effective at a large plant in Milan.

  6. You need to know the reasons for the scum formation; operational and/or organisms, especially filamentous bacteria. Options: You can introduce aerobic selector before the aeration tanks to reduce the amount of oxygen entering into them so as to reduce the growth of filamentous bacteria or you can introduce Chlorine to kill off the bacteria (depending on your final product goal). You can also reduce the Sludge Retention Time (SRT).

  7. Dear Zyaad,

    The scum is a normal phenomena floating in the secondary clarifier. Please explain if you have tube/lamellar settlers or normal circular clarifier woth bottom scrapper.

     

    If you have lamella/tube settlers then no need to worry about removing this scum as this will be beneficial in having a cleaner outlet water from weirs. However you can remove manually (simply using floor washing wiper with gentle hands) after every two weeks or so if you have a scape point made for this. Otherwise use swimming pool cleaning net with long rod to clean it.

     

    If you have circular clarifier with bottom scrapper then just simply make adjustment on the moving arm by putting rubber to skim out or guide the floating s to a scape point or use simple swimming pool cleaning rod with net.

     

    Also you need to look into if MLSS in you aeration are increased then or SV is increased then increase WAS flow rate to adjust and decrease RAS ratio.

     

    Please do any of the above will solve your problem.

     

    Best regards

    Mansoor Ahmed

  8. You have to check if there is a filemantous bacteria in your aeration basins this could be as many reasons: food to mass ratio and others investigate MLSS samples under microscope to determine which kind if suck bacteria you have

  9. If the scum is due to grease entering the biological treatment unit, you can start with a program to minimize grease entering the collection system or passing through primary treatment. I have treated grease problems at the lift stations with added mixing/aeration and biological cultures.