MLSS Concentration dropping in WWTP

Published on by in Technology

Our integrated wastewater treatment plant is now facing the problem low Mixed Liquor Suspended Solids (MLSS) concentration in the aerobic system.

The overall performance - removing Chemical Oxygen Demand (COD) efficiency and Total Suspended Solids (TSS) are normal, but the MLSS concentration in aerobic system keeps dropping. We even increased Return Activated Sludge (RAS) to try to build back the sludge contain but did not have success. 

How do we stop MLSS from dropping and why is it happening in the process?
Has anyone had similar experiences?

The wastewater source is petrol chemical industry wastewater.

 

Taxonomy

20 Answers

  1. This is an operational issue, please check the sludge aging into the digester, too much sludge lead to absorption of MLSS. Then it will end up decreasing the MLSS, for clarity seek go back and record all your recycling, desludging times and etc. Then you will get an answer, monitor your process regularly ask record from the process controllers.

    some question you need to ask yourself is that:

    1. Does your WWTWs operate 24/7?

    2. Does   your WWTWs monitored accurately?

    3. Does your WWTWs operate by competent personnel?

    4. Does handover done per shift?

    5. Do have record of DWF, PWF, and so on?

     

    If you have all meaning that you need to check on desludging record.

     

    Thank you,

    Phetla Mangena

  2. This is an operational issue, please check the sludge aging into the digester, too much sludge lead to absorption of MLSS. Then it will end up decreasing the MLSS, for clarity seek go back and record all your recycling, desludging times and etc. Then you will get an answer, monitor your process regularly ask record from the process controllers.

    some question you need to ask yourself is that:

    1. Does your WWTWs operate 24/7?

    2. Does   your WWTWs monitored accurately?

    3. Does your WWTWs operate by competent personnel?

    4. Does handover done per shift?

    5. Do have record of DWF, PWF, and so on?

     

    If you have all meaning that you need to check on desludging record.

     

    Thank you,

    Phetla Mangena

  3. Hi All,

    Thank you very much for all of your answers. My team checked through all the process and finally found sludge settling too good at the bottom of clarifier, which the concentration 3 times higher than normal time. After we increased RAS flow and unplug the RAS pump suction, the condition came back to normal.

    Thanks again for all of you.

    Best Regards,
    Zhengzhi

  7. Engr. Mansoor has given a good course of action to take. It is a question of checking through the process and by a process of elimination finding the cause of the problem. Once you have established the likely cause and you need to build up the biomass again consider the use of bioaugmentation to quickly build up a good biomass again.

  11. Lot of good points made here. Verify the influent loading hasn't changed that much. Was the WAS rate increased? If it was, decrease it but by no more than 10 % per week. If the WAS rate wasn't decreased and you are still losing MLSS, then decrease WAS rate by no more than 10% per week. Have you done a microbiological analysis (speciation)? Are the microbes essentially the same before the issue arose or not? If different, must determine why the change. Has something entered the RAS piping from the clarifier in which the flow is partially blocked? Did something like a bucket fall in the clarifier?

  12. This is due to input of higher influent load for immediate action required is to dilute the aeration tank volume wwith treated effluent.

    Some time it is due to filamentous growth of bacterias and to cope up pl add 0.3 ppm of active chlorine with recycling sludge to aeration tank

  14. Dear Zhengzhi Zhao,

    There are many points to focus for MLSS reduction in the Bio Reactor, you can make a check list as follows;

    1) Inlet Water might containing any antibiotic (disinfectants like Chlorine), please check if any change for any new chemical usage in the Processing Area?

    2) As you said, it is from Petrochemical Industry, any seepage/leakage of oil/petrol reaching to the Bio Reactor which inhibits Oxygen Transfer to Bacteria

    3) RAS Pump is not sufficient or may be clogged not returning sludge properly

    4) Temperature of the Bio Reactor is within the range (max. 37C), not increased?

    5) If you are giving Air by Blowers/Piping Grid with Diffusers, please check if these are not chocked (this could easily be done by checking DO Level 2 - 4 mg/l in the Reactor)

    6) Check Inlet Pollution Load, if it has sufficient to feed to bacteria, if COD is much less then you can add Jaggery (Sweet/Cane Sugar or else) for Bacteria to to have nutrients

    7) Please check inlet/outlet wastewater characteristics if different then designed?

    8) These could be the possible areas / checks to observe and rectify.

    Hope this would be enough by now.

    3 Comments

    1. I like to add that solids washout may lead to the same result, check decanted water S.S, but the case you have is most probably having TEL leaked to the system, if so , it will kill all your bugs. microscopic examination will help.  

  17. When the MLSS is dropping for no apparent reason it's usually caused by either of two reasons.  The first may be redworms and the resulting midge flies.  Red worms eat young protozoa and this drops MLSS.  We have a product Aquabac for Wastwater we use if this is the reason.   The second possibility is due to quaternary amines or other biocides.  if this is the reason we like to neutralize the disinfectant prior to the plant.

    In either case MLSS will settle like a rock, or very quick.  teamaquafix.com shows our Aquabac.

  18. Check and make sure your waste sludge pump is set correctly. Check your effluent SS to make sure you are not having blow through episodes. Also check the DO and COD. Low DO is bad, but high DO and low COD means your influent has changed. Have you checked the MLSS under the microscope for filaments?

  19. check the DO, a drop in D.O due to some problem with diffuses or blowers. oxygen is very important for aerobic process.

    drop in incoming COD, not enough food to sustain them in sufficient numbers.

  20. If you want to know the reason, you must provide a lots of information. To maintain the concentration of MLSS,  reduce the volume of waste sludge  at the moment.

    1 Comment

    1. The WAS is critical either set by a timer or a MLSS probe or by level control. Check this first and reduce slowly over say a week and MLSS should increase. More info is required but check food to mass ratio, and sludge age. I assume that the returned sludge is from final settlement tanks and a portion of this is wasted (WAS)..check level of hydrostats so that water is not being returned...