It is a little complicated. ...
Published by Joseph Cotruvo, President at Joseph Cotruvo & Associates, Water , Environment and Public Health
It is a little complicated. Are you treating drinking water?If you add enough chlorine to exceed the chlorine demand you will have some excess remaining for a time. If there is ammonia or amines in the water you can add enough chlorine to go to breakpoint where the ammonia is converted to nitrous oxide and nitrogen, anything after that will leave free chlorine in solution. The complete reactions with excess chlorine and organic carbon would continue slowly until all of the TOC has been converted to organochlorine or mixed halogen compounds if some bromide was in the water.
With wastewater the chlorine demand is so high (so much ammonia nitrogen) that wastewater is seldom taken to breakpoint. That means that wastewater is usually marginally disinfected, and has residual chloramines that are weak and slow disinfectants.