Applications of Environmental Aquatic Chemistry, 3rd Edition

143Chapter 4: Nutrients and Odors

RULES OF THUMB

1. The rate of ammonia removal by breakpoint chlorination is most

rapid at pH 8.3.

2. The rate decreases at higher and lower pH and at temperatures below

30°C.

3. Since Equations 4.9a through 4.9d produce H

+

and lower the pH,

additional alkalinity as lime might be needed if the concentration of

total ammonia >15 mg/L. Add alkalinity as CaCO

3

in a weight ratio

of about 11:1 of CaCO

3

to total ammonia–nitrogen (NH

3

–N).

4. The chlorine breakpoint (Figure 4.3) occurs theoretically at a

Cl

2

:NH

3

–N weight ratio of 7.6:1.

5. In actual practice, ratios of 10:1 to 15:1 may be needed if oxidizable