Civil Engineering Reference
In-Depth Information
is consumed by the organic nitrogen, free ammonia is released to instigate biological
instability in the distribution system.
Mixing.
Mixing at the point of application greatly affects the efficiency with which
monochloramine is formed. The reaction time between ammonia and chlorine is nearly
instantaneous at between 7 and 8.5. If chlorine is mixed slowly into ammoniated water,
organic matter may react with the chlorine and consume chlorine prior to monochlor-
amine formation. If ammonia is mixed slowly into chlorinated water, an excess of
chlorine may be present in localized areas, causing breakpoint chlorination and / or the
formation of dichloramine and nitrogen trichloride.
Blending Waters.
When chlorinated water is blended with chloraminated water, the
chloride:ammonia ratio will increase, causing breakpoint chlorination and formation
of dichloramine and nitrogen trichloride. The entire monochloramine residual can be
depleted. Therefore, it is important to determine how much chlorinated and chlora-
minated water can be blended without significantly affecting the monochloramine re-
sidual. Blended residual curves should be developed to determine the impact for each
specific blend.
Human Health and the Environment.
Kidney dialysis equipment users are the most
impacted by monochloramine use. If chloramines are not removed from the dialysate
water, chloramines can cause methemoglobinemia and adversely affect the health of
kidney dialysis patients. Chloramines can also be deadly to fish in aquariums. Chlor-
amine residuals should be removed from the water prior to addition to the aquarium.
Monochloramine DBP Formation.
The effectiveness of monochloramine in controlling
DBP production depends upon a variety of factors, including the point of addition of
ammonia relative to that of chlorine, the level of mixing, and pH of the water.
Monochloramine (NH
2
Cl) does not produce DBPs to any significant degree, al-
though some dichloroacetic acid can be formed. Also, cyanogen chloride formation is
greater with monochloramine than with free chlorine during secondary disinfection of
the distribution system.
Chlorine Dioxide
The major uses of chlorine dioxide for potable water treatment are:
Disinfection
•
Taste and odor control
•
Iron and manganese control
•
