Chloramine Disinfection 1

[Lan123]

When using Sodium hypochlorite and Ammonium Sulfate for chloramine disinfection, do we first add Sodium hypo followed by Ammonia or vice versa. What is most preferred method by the plant operators?

 

[bimr]

The formation of monochloramine can be accomplished by first adding ammonia and then chlorine, or vice versa. Ammonia is added first where formation of objectionable taste and odor compounds caused by the reaction of chlorine and organic matter are a concern. However, most drinking water systems add chlorine first in the treatment plant in order to achieve the required concentration and contact time (CT) to meet EPA’s SWTR disinfection requirements. Typically, the point of ammonia addition is selected to “quench” the free chlorine residual after a target period of time based on optimizing disinfection versus minimizing DBP formation. Because the germicidal effectiveness of monochloramine is a factor of 200 less than for free chlorine, extremely long contact times are required for monochloramine to meet EPA disinfection CT
requirements. Therefore, if ammonia is added first, a means of ensuring that CT requirements are met must be developed.

To ensure that these compounds are not formed, common practice was to limit the chlorine to ammonia ratio to 3:1. However, because of problems such as nitrification and biofilm growth, which can be caused by excess ammonia, current practice is to use a Cl2:N ratio in the range
of 3:1 to 5:1, with a typical value of 4:1.

http://www.epa.gov/ogwdw/mdbp/pdf/alter/chapt_6.pdf

 

[Lan123]

Thanks bimr for the reply. Let me change my question now. In case we want to chloramine disinfect secondary municipal effluent, will the addition of chlorine first increase the chlorine demand?

 

[bimr]

My understanding is that chloramines are not as effective as chlorine. Here is an interesting paper advocating the use of chlorine first:

http://www.aaee.net/Downloads/EEJournalV9P2.pdf