IN CHLORINE SYSTEMS AND THE FORMATION OF CHLORAMINES
One of the important steps in the treatment of a water supply is chlorination. Most objectionable odors and tastes present can be removed while disinfecting water with chlorine gas during the treatment process. Chlorine also inactivates undesirable materials sometimes present in water such as sulfides, sulfites, ferrous iron, miscellaneous organic matter, etc.
In large open reservoirs, it is difficult to maintain the necessary level of chlorine due to the fact that it combines with organic matter and is dissipated in sunlight. In order to maintain a desired chlorine level, anhydrous ammonia can be added before the chlorination step. This complexes the chlorine in the form of chloramines. Treatment of water with chloramines is referred to as chloramination, or contained residual chloramination.
The actual reactions involved with the formation of chloramines are:
FORMATION OF AMMONIUM HYDROXIDE
NH3 + H20 → NH4OH
Anhydrous Ammonia Water Ammonium Hydroxide
FORMATION OF HYPOCHLOROUS ACID
Cl2 + H20 → HOCl
Chlorine Water Hypochlorous Acid
FORMATION OF MONOCHLORAMINE
NH4OH + HOCl → NH2Cl
Ammonium Hydroxide Hypochlorous Acid Monochloramine
FORMATION OF DICHLORAMINE
NH2Cl + HOCl → NHCl2
Monochloramine Hypochlorous Acid Dichloramine
The ratio of monochloramine to dichloramine is dependent upon the pH of the water being treated. At a pH of 8.5, monochloramine is the only compound formed. At a pH of 5.0, dichloramine is the only compound formed.
Each water system must be analyzed individually to determine if the addition of ammonia is required in the disinfection process. Such things as reservoir size and ammonia content of raw water must be considered. The ratio of chlorine to ammonia required for the formation of chloramines varies from 8:1 to 1:1, depending upon the amount of ammonia present in the raw water. At a ratio of 10:1 the chlorine will tend to oxidize ammonia to form nitrogen and water.
Click here for the Anhydrous Ammonia Material Safety Data Sheet
