NO2-N decrease and NO3-N increase while we lower the DO in the high chloride (~10,000 ppm) wastewater

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the petrochemistry and chemical wastewater we deal ,

1.the inflow : COD~1,000 ppm, NH3-N 20~30 ppm,TKN ~50 ppm; the process parameter,HRT ~12 hrs for one aerotion tank (DO 2~3 ppm) and HRT ~12 hrs for the other aerotion tank (DO 6~8 ppm) ,

2.the effluents: COD ~200 ppm,NH3-N 2~20 ppm,and NO2-N 2~20 ppm, NO3-N 0~2 ppm.

3.while we lower the DO of the second aerotion tank from 6~8 ppm to 3~4 ppm,then the NO2-N change from 2~20 ppm to 0~2 ppm, and NO3-N change from 0~2 ppm to  2~20 ppm.

4.what happen to the second aerotion tank ,when we change the DO from 6~8 ppm to 3~4 ppm.

5.the  NO2-N (2~20 ppm) will negative impact the sludge of aerotion tank ,and make the reduction rate of NH3-N is unstable, and the NH3-N of effluents is 2~20 ppm.

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7 Answers

  1. Hi Lin, may you know the nature of your wastewater or industrial process and the flow managed?

    Also probably all of us will appreciate the feedback about your results of suggested solutions, thanks.

    2 Comments

    1. the COD of inflow is about 1,000 ppm, the wastewater deal by settling tank ,activated sludge tank(MBBR/first and second ​aerotion tank) ,DAF and sand filter, the COD of effluents is below 100 ppm,the process for COD remove is all right;the NH3-N of inflow is about 20~30 ppm,the NH3-N reduction rate deal by aerotion tank is not stable, and the NO2-N and NO3-N generate in the aerotion tank is not normal. I guess the DO may be a factor, but I do not know why we lower the DO in the  second aerotion tank, and the NO2-N is decreased and NO3-N is increased.

      1 Comment reply

    2. the wastewater come from the units of Epichlorohydrin, vinyl chloride, polyvinyl chloride etc.,and the flow rate of this wastewater is about 15,000~20,000 M3/D.

      1 Comment reply

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  2. Dear Mr. YAN

    From my experience, I will use COD/N ratio by using anoxic but 12 hr is not enough. If you use AS or SBR you need more time for COD 1000 and TN 50 for digestion, The first tank you are correct on operation but for the second you should decresing DO to 0.5ppm for Anoxic and COD will be remove as well. more infor aggasit2012@gmail.com  and whatapp +66917027747

    1 Comment

    1. we deal the wastewater by MBBB,first aerotion tank and second ​aerotion tank.the process for COD remove is all right,but the NH3-N reduction rate is not stable,we lower the DO in the  second aerotion tank, althought the NO2-N is decreased and NO3-N is increased,but the NH3-N reduction rate is still all right.

  4. You have a typical "nitrite lock" phenomena, in which during the startup or temperature change or shock loading conditions, nitrite will accumulate.  Nitrite concentration, when high enough, will cause inhibition of nitrite oxidation bacteria (NOB).  But your influent ammonia is not too high, this transient process will pass and the change of DO may not be the cause of the nitrite reduction.  But the nitrification in your system is still not complete, so keep you sludge  age long and keep the feed steady and maintain DO at > 2 mg/L in both reactors.   The problem should go away.  You don't have to spend money to change process, I don't believe.    

    1 Comment

    1. to improve this situation in our plant, we add the other sludge to this system, and the NH3-N ​reduction rate ​will be  promoted rapidly(about 7~14 days), but the NH3-N will change to NO2-N,until we add the other sludge to this system the same ,but we lower the DO, and the NH3-N change to NO3-N. now we will look on the NH3-N ​reduction rate will be stable,in the lack of NO2-N in our aerotion tank. ​

  6. I am afraid your info is still lacking a lot of essential input to have a full massbalance. NOrmally: first denitrification tank with very low (like Paolo suggested) O2 0.2-0.5ppm, then the nitrification 1,5-2,5 mg/l (why you need 5-6 mg/l? TO me that is a HUGE unnecessary destruction of electricity with that kind of heavy aeration).

    BUT you need a large recirculation of the ML (mixed liquor) of the second tank back to the first, to bring back NO3 (with healthy sludge you do not have elevated levels of NO2) to the first tank for denitrification. This could be anything between 50% (compared to the feedflow) up to 300 or even 500% recirculation....but not sure if your system has been designed hydraulically for that (overflows, pumps etc). To know what the denitrification recirculation rate shoudl be you need to make the massbalance of N and C, using the usual stoechiometric reactions of nitrification/denitrificationMind: .

    Denitrification recirculation is something else than sludge recycle (that is typically 100%) that brings back sludge from the secondary clarifier to your (preselector?) mixtank before the first 12h denitrification tank.

    What puzzles me is that to me it seems you have just enough (even a bit of shortage) of Nkj versus COD, (easy circumstances C:N = 100/15 tough: 100:5) so most, if not all, would be needed to built enough biomass....taking away the need for denitrification. And with 80% COD removal, and such fluctuatiing N numbers in your effluent it sounds to me your system shoudl be able to perform more stable, no NO2, no NH3, and only couple of mg/l of NO3.

    If you nonetheless still need nitri/denitrifucation, why don;t you get advice from organisations like COlsen (which incorporates annamox bacteria (red coloured) into your normal activated sludge saving hugely on your oxygen electrical consumption) or RHDHV (Royal Haskoning DHV) that have the NEREDA, granular aerobic sludge (cancelling your secondary clarifier, and potentially one of your activated sludge tanks).


    Good luck!

    1 Comment

    1. the process for ​COD remove is ​all right, but ​the NH3-N ​reduction rate ​is not stable.in ​our plant, we ​add the other ​sludge to this ​system, and the ​NH3-N ​​reduction rate ​​will be ​ promoted rapidly(about 7~​14 days), but ​the NH3-N will ​change to NO2-N,​until ​we add the ​other sludge to ​this system the ​same ,but ​we lower the DO, and the NH3-N ​change to NO3-N.​ now we ​will look ​on the NH3-​N ​reduction ​rate will ​be stable,in ​the lack of NO2-​N in our ​aerotion tank, or we add the other ​sludge to this ​system normality,to keep the NH3-N ​reduction rate ​.