Elimination of Organic Nitrogen in a WWTP

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Hi All, 

I was wondering if it is possible to get NGL = NTK at the outlet of a WWTP. My understanding is that there is a small fraction of organic nitrogen which will never be treated, so NGL will always be higher than NTK. 

If anyone can help, that would be amazing, 

Thanks a lot

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9 Answers

  1. You get NGL > NTK because there is always a fraction of Nitrate/Nitrite which does not get  removed. It would be impossible to remove them totally unless there is a proper tertiary treatment method. 

  2. Ismail Alaoui 

    You are right that Total Nitrogen TN (NGL) is always higher than Total Kjeldahl Nitrogen TKN (NTK) in the effluent of a biological WWTP. However this is NOT because there is always residual organic nitrogen but because there is always some residual oxidized nitrogen N-NOx (nitrite + nitrate nitrogen). As explained by others TKN = organic nitrogen + ammonia nitrogen and TN = TKN + N-NOx. Hence N-NOx > 0 implies TN > TKN.

    Regards,

    Bruno

  3. Here is a small summary of the different forms of nitrogen usually sought after in wastewater analyzes: 

    - Nitrates: these are NO3 in solution. The pollution is calculated in mgNO3 / L. 
    - Nitrogen nitrate : also represents nitrates but is expressed in milligram of nitrogen per liter (mgN / L) - Nitrogen nitrate = Nitrates / 4.43 --- (4.43 = Molecular weight of NO3 / mass of nitrogen). 
    - Nitrites: these are NO2 in solution, very toxic for aquatic life. The pollution is calculated in mgNO2 / L. 
    - Nitrous nitrogen:also represents nitrites but expressed in milligrams of nitrogen per liter (mgN / L) - Nitrous nitrogen = Nitrites / 3.28 --- (3.28 = NO2 molecular weight / mass of nitrogen). 
    - Kjeldahl Nitrogen (NTK): It represents the sum of the organic nitrogen and the ammoniacal nitrogen contained in the water. It is expressed in milligram of nitrogen per liter (mgN / L). 
    - Global Nitrogen (NGL): It is the sum, expressed in milligrams of nitrogen per liter, of Kjeldahl nitrogen, nitrates and nitrites - NGL = NTK + Nitrogen + Nitrogen Nitrogen. 

    Hope it gives you clarification.

     

    Regards,

     

    Sushant Kumar

  4.  Nitrogen exists in several forms. The principal nitrogen types of concern to wastewater treatment are: total Nitrogen (t-N), Total Kejeldahl Nitrogen (TKN), Ammonia (NH4 ), Organic Nitrogen (org-N), Nitrate (NO3 ), and Nitrite (NO2 ). Concentrations are reported in mg/L, as Nitrogen (N).

    treatment facilities with total- nitrogen  effluent limits can oftentimes reduce the  organic nitrogen  to less than one mg/L by subjecting  wastewater  to strongly anaerobic and  organically -rich conditions. Nitrification. Ammonia removal is a strictly aerobic biological process.

    Total Kejeldahl Nitrogen (TKN). TKN is made up of Ammonia (NH4 ) and organic-Nitrogen. A municipal wastewater treatment plant with an effluent containing more than 5 mg/L TKN is not fully nitrifying.

    TKN = NH4 + org-N

    organic-Nitrogen (org-N). A small fraction, typically one or two milligrams per liter, of the organicNitrogen is not amenable to biological treatment and passes through the treatment facility unchanged. A municipal wastewater treatment plant that is effectively nitrifying generally contains less than 3 mg/L organic-Nitrogen.Proteins represent a large portion of organic nitrogen and carbon in wastewater treatment effluents, but their detailed characteristics and their role and fate in receiving waters are virtually unknown.

    Treatment plants convert the majority of the incoming nitrogen to nitrogen gas in a three step biological process.

     Step 1. Organic-nitrogen is converted to ammonia-nitrogen (NH4 ) by a mostly anaerobic process called Ammonification.

    Step 2. Ammonia-nitrogen (NH4 ) is converted to nitrate-nitrogen (NO3 ) by an aerobic biological process called nitrification.

     Step 3. Nitrate-nitrogen (NO3 ) is converted to nitrogen gas biologically in a low-oxygen (anoxic) environment. During denitrification, nitrogen gas bubbles harmlessly out of wastewater into the atmosphere.

    Ammonification.

     The majority of the nitrogen contained in raw sewage (urea and fecal material) is converted from organic-nitrogen to ammonia (NH4 ) as it travels through sewer pipes. As a result, the majority of the influent nitrogen is ammonia (NH4 ), although some organic-nitrogen remains. In most plants, less than 2 mg/L of organicnitrogen passes through the treatment plant untreated. The rest is converted to ammonia (NH4 ).

    Ammonification is mostly an anaerobic process. It is sometimes called hydrolysis. Most treatment plants do nothing to enhance organic-nitrogen removal; it is not managed. However, treatment facilities with total-nitrogen effluent limits can oftentimes reduce the organic nitrogen to less than one mg/L by subjecting wastewater to strongly anaerobic and organically-rich conditions.

      Nitrification.

     Ammonia removal is a strictly aerobic biological process. Technically, bacteria convert ammonia (NH4 ) to nitrate (NO3 ); it isn’t really “removed.” Nitrification only works on ammonia (NH4 ). Organic-nitrogen is not converted directly to nitrate (NO3 ); it must first be converted to ammonia (NH4 ), and the ammonia (NH4 ) converted to nitrite (NO2 ) and then nitrate (NO3 ). Nitrifying bacteria are slower growing and more sensitive to environmental upset than BOD removing bacteria. Generally, nitrification occurs only under aerobic conditions at dissolved oxygen levels of more than 1.0 mg/L. In activated sludge facilities, nitrification requires a long retention time, a low food to microorganism ratio (F:M), a high mean cell residence time (measured as MCRT or Sludge Age), and adequate pH buffering (alkalinity).

  5. Hi. Ismael. I have been remedying ww using phyto- R using appropriate plants.. This mode could be used to fix N2 in plants..Organic Botanists can elaborate. Pl.. w wshs .. 

  6. Biological process to treat domestic wastewater, should have residual non-biodegradable and soluble organic nitrogen at a level of approx. 2.5 to 3 mg/L TN in the effluent. You can further remove them by adsorption by activated carbon or by RO.

  7. Sir.......We have been treating such a problem with great success for many years now. We have engineering reports from several WWTP that show excellent results.

    Let us have an email chat, perhaps we can solve your problem with ease /

     

    pettman@soleco-technology.com 

    Hugh.

  8. Hi Ismael, the dissolved iorganic (non-biodegradable) nitrogen stands for 1,5-3 mg/l for a typical domestic sewage water.

    1 Comment

    1. Dear Phillipe, dissolved inorganic N (NH4, NO2, NO2) which has reliance to WWT processes; I have no idea about non-biodegradable inorganic N. The name of the game here is TKN; organic N. Microfiltration has limitations in removal of nitrogen fractions. We have difficulties in reaching a total N of 10 mgN/L in one of MBR facilities? What is the actual source of organic N is not easy? So, assuming of 2 mg N as TKN in the effluent (German DWA approach in ATV-A 131) is just to make the life of the process engineer easy in doing a N mass balance.

      So, organic N can be non biodegradable if of biological origin as intermediate metabolites or of unknown industrial waste streams. 

       

  9. I'm not sure what do you means exactly with NGL ...

    However, normally it goes like this:

    Total Nitrogen (TN) = Organic Nitrogen (Norg) + Ammonia nitrogen (NH4-N) + Inorganic Nitrogen (NOx-N)

    While Kjeldahl nitrogen is the sum of Norg and NH4-N

    At wastewater outlet you will always have some residual Norg carried out as part of the suspended solids composed mainly of activated sludge cells. ATV Standards suggest a 2mg/L value after a conventional secondary clarifier.

    Tertiary treatment like microfiltration will surely decrease this value.

    I hope it can help ...

    1 Comment

    1. Thank you for your answer. I was referring to TN when I said NGL. I was wondering if it is possible to eliminate at 100% Kjeldhal Nitrogen and get at the outlet of a WWTP with a reuse purpose, TN=N-NO3.  is it feasible?

      1 Comment reply

      1. Indeed, there is some contradiction in your original question. If your task is to get close to TN=N-Kjeld then you need to reduce as much as possible N-NOx. While if your target is to get close to TN=N-NO3 then you should look to reduce N-Kjeld and therefore N-org and N-NH4. From your comment, I assume that your goal is the latest. 

        My second concern is related to the fact that in the real world, it is usually impossible to get concentrations equal exactly to "0". So you should better set an acceptable threshold (less than ...) rather than try to get to zero.

        Then, on the technological side you should act on three components: 1) N-org (in suspended solids); 2) N-org dissolved and 3) N-NH4 dissolved. 

        The first can be reduced by tertiary filtration (sand or active carbon --> microfiltration --> ultrafiltration --> RO depending how much you want to push your system).

        N-org dissolved can be reduced by improving biology in your system but if it is composed by recalcitrant compounds you could also think about adsorbtion on GAC or advanced oxydation technologies or again RO

        N-NH4 can be reduced by improving nitrification or again by use of tertiary treatment.