The DO after degassing process

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Hi everyone,

The wastewater is treated by Anoxic, Oxic, and by degassing process.

The sludge after the DAF process will return to the Anoxic process.

Does the DO after degassing process meet the need of the microorganism in Anoxic tank? and to maintain the denitrification reaction rate (about 50%) in the A/O process ? while the DO of Oxic process could be 5~8 ppm.

your feedback much appreciated

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5 Answers

  1. Hi Lin, from what you have said (nitrification is unstable at higher DO levels in the oxic stage) that the reactor is too small, and the micro-organisms are active converting COD to biomass with the available food and oxygen.  It will only be when the COD food source is very low that nitrification will occur, or when DO levels are low.  So - have you measured COD values in the effluent both when the DO is high and when the DO is low in the oxic reactor.  Also is your reactor a completely mixed reactor or do you have at least 2 but preferably more oxic stages so that the COD food gets less and less in the later stages, allowing nitrification to take place?  It would also be useful to know what the ammonia and nitrate levels of your final effluent are.

    1 Comment

    1. Dear lan,

      1.the volume of anoxic and oxic tank both is about 10,000 M3, jet or diffuser type mixed reactor. the Inflow is about 20,000 M3/D, the MLSS of  both process is 3,000~4,000 ppm.

      2.the COD of influent is about 1,000 ppm, the COD of effluent is less than 80 ppm, the COD reduction rate is all right in the high or low DO of the oxic process.

      3.the NH3-N of influent is about 30 ppm, the TKN of influent is about 60 ppm, the NH3-N of effluent is 10 ppm or higher, and the NO2-N produced in the high DO case, while we lower the DO to ~3 ppm, the NH3-N of effluent is less than 3 ppm, the NO2-N is disappear and NO3-N produced in the low DO case.

      4.we check the sludge by NGS (Next Generation Sequencing), and find some clue, but we still not know what happen due to the change of DO in the oxic tank.

       

      1 Comment reply

      1. Hi Lin,  my first thought was that you may be getting some anoxic conditions within the MLSS flocs at the lower DO levels, but it seems the literature does not support this theory.  The fact that you get some nitrite in the higher DO conditions seems to imply the temperature of the wastewater is quite high (>25 degrees C), which may also affect other biological processes.  Lastly, having a single mixed aerator is not normally ideal for nitrification.  If possible try to install baffles to divide the reactor and obtain more of a plug flow condition, but test this out on a laboratory scale first.  Best wishes

  2. apologies - my system closed when I was half way through. I wanted to understand whether you recirculate after the oxic stage back to the anoxic stage to be able to convert the nitrates formed in the oxic stage to nitrogen gas in the anoxic stage.  This is a normal BNR sequence, and this stream is likely to carry a small amount of free oxygen into the anoxic stage, but it will be quickly used up when combined with the return sludge.  You would be recirculating at least 100% or more of the flow through the oxic tank back to the anoxic tank.  

    1 Comment


    1. 1.The wastewater of the oxic stage do not back to the anoxic stage now. The sludge ​of the oxic stage deal by the DAF ​process, and ​return to the ​anoxic process
      2.if the DO of the oxic stage is 5~8 ppm, the nitrification reaction rate is not stabile, we think the high DO weak the active of the anoxic bacteria in the sludge, until we lower the DO of oxic stage to ~3 ppm, and the nitrification reaction is stabile, the denitrification reaction rate will be 40~50%.

  3. Hi Lin, as Philippe has said, the DO in the sludge return should be very low and not a problem.  However I am trying to understand your process.  You say the treatment seq

    1 Comment

    1. 1.The ​wastewater is ​treated by ​Anoxic, Oxic, ​and by ​degassing ​process.The ​wastewater of ​the oxic stage ​do not back to ​the anoxic ​stage now. The ​sludge ​of the ​oxic stage deal ​by the DAF ​​process, and ​​return to the ​​anoxic process ​
      2.if the DO ​of the oxic ​stage is 5~8 ​ppm, the ​nitrification ​reaction rate ​is not stabile, ​we think the ​high DO weak ​the active of ​the anoxic ​bacteria in the ​sludge, until ​we lower the DO ​of oxic stage ​to ~3 ppm, and ​the nitrification ​reaction is ​stabile, the ​denitrification ​reaction rate ​will be 40~50%.

  4. Don't worry, there is no issue, the amount of dissolved Oxygen is usually negligible and cannot interfere with nitrate removal

    1 Comment

    1. the DO ​​of the oxic ​​stage is 5~8 ​​ppm, the ​​nitrification ​​reaction rate ​​is not stabile, ​​we think the ​​high DO weak ​​the active of ​​the anoxic ​​bacteria in the ​​sludge, until ​​we lower the DO ​​of oxic stage ​​to ~3 ppm, and ​​the nitrification ​​reaction is ​​stabile, the ​​denitrification ​​reaction rate ​​will be 40~50%.​

  5. ORP values are going to be more meaningful for the operator and you should observe the changes in ORP as an indicator of desired metabolic functions post degassing.

    1 Comment

    1. the Anoxic, Oxic process,  we control the DO both is about 2~3 ppm now, and the  denitrification reaction rate is about 40~50%. if we control the Anoxic process DO is 2~3 ppm, and the Oxic process DO is >4 ppm earlier in the system, the nitrification reaction rate is not stabile. we do not know why the DO just range 1~2 ppm, and the active of microorganism is different totally.