Break Point Chlorination

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I am looking for some insight on breakpoint chlorination in RO rejects containing Ammonia. In ionized form. There is about 1 -7ppm of Ammonia as N. Need to bring it down to 0.3 ppm by Breakpoint Chlorination.

What dose ratio should be considered to convert Ammonia into Nitrogen gas?

AWWA recommends 12: 1 ratio. Will there be Nitrogen Trichloride formation. But the pH of the solution is between 7.5 to 8.5. Nitrogen Trichloride usually forms at lower ph about 4.2.

Can you please recommend possible solutions here. Thanks in advance

Regards,

Abilash

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7 Answers

  1. This is going to be very difficult.  Chlorination reacts with ammonia to form mixed mono and dichloramines.  These will de-gas if the water is then sprayed.  Because the levels of ammonia appear to vary then the level of chlorine required will vary.  I don't think you will achieve conversion to nitrogen gas.

  2. although the stoichiometric ratio is 1:7, it is always recommended to go above this to say 1:10 (we found this adequate in another application).  However you may also want to consider an alternative for ammonia reduction such as the natural zeolite - clinoptilolite which is able to reduce ammonia to acceptable levels through an ion exchange/adsorption process.  When you ammonia is as high as 7 ppm, you will require high chlorine doses which could be costly.

  3. The ratio based on stoichiometry is 1:7 meaning for each free Nh3 need to dose 7 my/l free chlorine 

    Anything beyond this will form free chlorine in water

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  4. hy are you concerned about chloramine in the reject water?  12:1 should be more than enough to get to nitrogen.

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  5. Abilash,

      My recommendation is to connect with a qualified/certified Chemist and have him/her analyse the RO reject water and recommend safe chemical treatment strategies to reduce the Ammonia. It may be possible to use breakpoint chlorination but if NCl3 does form (as you seem to already know) that can cause an explosion so bench testing on your own may not be the wisest option.

      Again a qualified/certified Chemist can provide a safe and effective treatment solution to your question.

    Best Regards

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