The loading (F/M value) effect the efficiency of organotrophic and nitrifying bacteria

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Dear all,

1.One of the inflows is stopped because of the regular inspection, and the COD loading is decreased, but the NH3-N loading is the same. The COD reduction rate is keeping about 90%, but the NH3-N reduction rate is decreased from about 90% to 0%.
(1)the wastewater is decreased from about 18,000 M3/D to 11,000 M3/D.
(2)the inflow COD change from 1,000 ppm to 700 ppm.
(3)the inflow NH3-N change from 20 ppm to 40 ppm.
(4)the MLSS of activated sludge is decreased from about 3,000 ppm to 2,000 ppm.

2.We think,
(1) the loading of COD is decreased, the MLSS is decreased to keep the F/M ratio, so the COD reduction rate could keep the same (about 90%).
(2)The MLSS is decreased, the nitrifying bacteria in the sludge is decreased, but the NH3-N is increased, so the NH3-N reduction rate is decreased from about 90% to 0%.

3.Does someone have the knowledge or experience to assist to check our hypothesis, and help us to make the next step, thanks.

 

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4 Answers

  1. I agree with most what has already been said. I would make sure that you control your MLSS to give an F:M of around 0.1 a sludge age of a least 12 days. If the pH is around neutral and you have sufficient alkalinity you should have no problem re-establishing the nitrifier population. I would never buy nitrifiers, grow your own. If you need to add them, there is something wrong with the process; sort that out and they will return naturally within a week or so (depending on the operating temperature). Keep the DO above 2 mg/l initially and reduce depending on effluent quality once nitrification has stabilised. Let us know how you get on. If you lose nitrification under these circumstances then check for inhibition due to something in the influent (ISO 9509).

    1 Comment

    1.  

      1.The pH is changed from about 6.6 to  5.6.

      2.The abnormal time have been two weeks, and the temperature is about 35℃.

      3.we pump the sludge from other system (which is good to NH3-N reduction) as usually, but this time  the NH3-N reduction rate and MLSS is poor to improve .

      4.we have increase the pH, from 5.6 to 6.0 (now), the target is about 7.

      5.Could you kindly offer me the ISO 9509, thanks.

      1 Comment reply

      1. Dear Lin. Is the wastewater domestic or industrial?

        1. Do you know the cause of the pH drop? Is this the untreated wastewater or after treatment? You will not nitrify at pH 5.6

        2. Is this wastewater temperature? You are on the edge of nitrification at 35oC. You will need sludge age of at least 12 days, preferably 18 days for full nitrification at this temperature.

        3. If you have a sludge from another plant, this is good. But, the conditions need to okay. I suggest you raise the pH to at least 6.5. What is the alkalinity? You will need at least 300mg/l as CaCO3 for 40 mg/l NH3 and a minimum of 50mg/l after full nitrification to prevent pH drop, Do you denitrify and recover the alkalinity?

        4. Is this pH increase after treatment or have you increased by manual alkaline addition?

        5. ISO9509 is available on the internet

  2. What is the pH range and also the alkalinity? Nitrifying bacteria need to have a minimum of 4.5+ mg/L of alkalinity to 1 mg/L N-NH3 to achieve sequential Nitrogen-Ammonia reductions and they need same ratio (4.5::1) of dissolved oxygen for metabolic activity. This is a good way to start if you have the data. As below comment, remember this is a flow thru treatment scheme and adding Nitrifiers from an incubator is a BMP.  What other process changes have you made?

    1 Comment

    1. 1.The pH is ​changed from ​about 6.6 ​to  5.6. Now ​we have ​increase the pH from 5.6 to 6.​0, the ​target is about ​7.

      2.The ​DO is about 3 ppm, although the DO is varyed from 1.5 to 3.5 ppm.

      3.we pump the ​sludge from ​other system (​which is good ​to NH3-N ​reduction) as ​usually, but ​this time  ​the NH3-N ​reduction rate  is ​poor to improve ​.

  3. One of the key things is bacterial population and sludge age.  If the bacteria are too young then you may have wasted out too many nitifiers.  They are extremely sensitive, as you know.  I would start with adding liquid nitrifiers (nitrosoma/nitrobacter blend usually kept cold in a suspension).  4 gallons per shift to each aeration basin to grow back the nitrifying colonies.  You should be able to monitor the mixed liquor under the scope for the increase in colonies.  Should take about a week but you should see an impact day 3. Thanks, Sean

    1 Comment

    1. 1.The sludge we drain is 5 mins every 30 mins, and now we plan to lower the drain time, to increase the sludge age.

      2.we pump the ​​sludge from ​​other system (​​which is good ​​to NH3-N ​​reduction) as ​​usually, but ​​this time  ​​the NH3-N ​​reduction ​rate  is ​​poor to improve ​​.

  4. Hi Lin,

    You are right, the MLSS will gradually decrease in accordance with the lower load. To give you a more complete answer one would also need to know: 1. How long has the load been lower or at what date did the load decrease, 2. What is the reactor water temperature, 3. at what sludge age are you operating the reactor and 4. what procedure do you follow to control the sludge age/MLSS concentration? Regards, Andre

    2 Comments

    1. Hi Lin,

      The reactor temperature is much higher than my typical experience, but this should have a positive impact on nitrification. Because we don't know what the sludge age is, I would recommend that the MLSS is maintained at higher levels (and higher sludge age) rather than lower levels as a safety precaution for nitrification. From the info available I would say that the current problem was due to a reduction in alkalinity (due to nitrification or feed) coupled with an increase in ammonia concentration. Nitrification will utilise alkalinity resulting in pH instability and lower pH values. Lower pH values will result in lower nitrification rates (pH below 7.0 will significantly reduce nitrification rates as the pH reduces). I would therefore recommend that alkalinity/pH is adjusted upward by lime (or other base) dosing. pH adjustment should be accurately controlled as a high pH will also impact negatively on nitrification.

      If alkalinity/pH is not the problem, it could be some nitrification inhibitory substance in the feed or which became more prominent due to the change in load.

      Regards

    2. Q1. How ​long has the ​load been lower ​or at what date ​did the load ​decrease,
      A1. The load lower initiate date is 8/22, and the NH3-N ​reduction rate ​decreased ​is 8/28.

      Q2. ​What is the ​reactor water ​temperature,
      A2. ​The temperature ​is about 35℃.​

      Q3. ​what sludge ​age are you ​operating the ​reactor
      A3.The sludge ​we drain is 5 ​mins every 30 ​mins, the ​sludge age we do not calculae yet.

      Q4. ​what procedure ​do you follow ​to control the ​sludge age/MLSS ​concentration? ​
      A4.To maintain the MLSS is about 3,000~3,500 ppm.