Break Point Chlorination

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

Taxonomy

• Treatment
• RO Systems
• Chlorination
• Reverse Osmosis
• Chlorine Dioxide Treatment

7 Answers

1. One other option would be to lower the pH to about 6.5 this should essentially cause all the ammonia to convert to free form where it can be removed by aeration.

2. 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.

3. 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.

4. 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

   1 Comment

   1. Thanks, the intention is to form N2 from Ammonia as we have limits for Ammonia, Total Nitrogen, Nitrate in tge reject discharge. As NCl3 is pH dependent, I am sceptical if it's gonna form.

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

   1 Comment

   1. Thanks, Intent is to convert NH3 to N2 using Breakpoint. We don't want to form NCl3. Given the water pH being 7.5 to 8.5, is there a chance of NCl3 being formed?

6. 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

   1 Comment

   1. Thanks Louis, Testing would not be feasible until we get to site for commissioning. I am sceptical about NCl3 formation due to the water pH. Do you have any inputs on what would be the reaction time for Breakpoint chlorination.

7. Why not try Sodium bi sulphate?

   1 Comment

   1. Sodium Bisulphite is provided for controlling the ORP to -100mV to 100mV after breakpoint chlorination.