TM 5-813-3/AFM 88-10, Vol 3
the formation of chloramines until the ratio of ele-
bed it is again airlifted and repeats the cycle. Upflow
mental chlorine to ammonia compounds is about 5 to
continuous backwash sand filters require no backwash
1. Further addition of chlorine results in the oxidation
valves, storage tanks, or backwash pumps, therefore
of chloramines to gaseous nitrogen and nitrogen
their operation is greatly simplified.
oxides, which decreases the quantity of chloramines
2-7. Disinfection.
present. After all of the chloramines have been oxi-
dized, additional chlorine added to the water forms
Disinfection involves destruction or inactivation of
only free available chlorine. The point at which all of
organisms which may be objectionable from the stand-
the chloramines have been oxidized and only free chlo-
point of either health or esthetics. Inasmuch as the
rine is formed is called the "breakpoint ." If no am-
health of water consumers is of principal concern to
monia is present in the water, there will be no break-
those responsible for supplying water, design of facili-
point. The chlorine required to reach the breakpoint is
ties for disinfection must necessarily be carefully
usually about 10 times the ammonia nitrogen content
executed.
a. Chlorination. The application of chlorine to water
of the water. However, in certain waters, because of
the presence of other chlorine consuming substances,
is the preferred method of disinfecting water supplies
as much as 25 times the ammonia nitrogen concentra-
at military installations.
(1) Definitions. Terms frequently used in connec-
tion may be required. Enough chlorine should be added
past the breakpoint to ensure an adequate free
tion with chlorination practice are defined as follows:
(a) Chlorine demand. The difference between
chlorine residual.
(c) Marginal chlorination. Marginal chlorination
the concentration of chlorine added to the water and
involves the application of chlorine to produce a de-
the concentration of chlorine remaining at the end of a
sired level of total chlorine residual regardless of the
specified contact period. Chlorine demand varies with
relative concentrations of free or combined chlorine
the concentration of chlorine applied, time of contact,
present. In marginal chlorination the initial chlorine
temperature, and water quality.
(b) Chlorine residual. The total concentration of
demand has been satisfied but some oxidizable sub-
stances remain.
chlorine remaining in the water at the end of a speci-
fied contact period,
(d) Chlorine dosages. Figure 2-4 provides mini-
(c) Combined available residual chlorine. Any
mum cysticidal and bactericidal free chlorine residuals
and minimum bactericidal combined chlorine residuals
chlorine in water which has combined with nitrogen.
--
The most common source of nitrogen is ammonia, and
for various pH and temperature levels. Since water-
borne bacteria are the major concern at fixed installa-
compounds formed by the reactions between chlorine
tions, minimum bactericidal levels will be maintained
and ammonia are known as chloramines. The disinfect-
in treated water in all parts of the distribution system
ing power of combined available chlorine is about 25 to
100 times less than that of free available chlorine.
under constant circulation. Even at lower pH levels,
(d) Free available residual chlorine. That part of
free chlorine residuals should not fall below 0.2 mg/L
and combined chlorine residuals should not fall below
the chlorine residual which has not combined with
2.0 mg/L. If marginal chlorination is practiced, the
nitrogen.
(2) Chlorination practice.
total chlorine residual must not be less than 2.0 mg/l.
Whenever epidemological evidence indicates an out-
(a) Combined residual chlorination, Combined
residual chlorination entails the application of suffi-
break of a nonbacterial waterborne disease such as
amebiasis, infectious hepatitis, or schistosomiasis in
cient quantities of chlorine and ammonia, if ammonia
the area of a fixed military installation, cysticidal free
is not present in the raw water, to produce the desired
chlorine residuals shall be maintained in the water
amount of combined available chlorine (chloramine) in
supply. Further guidance on disinfection requirements
a water. If enough ammonia is present in raw water to
may be obtained from the Surgeon General's office.
form a combined chlorine residual, only chlorine need
Air Force policy on minimum chlorine levels is estab-
be added to the water. Combined residual chlorination
lished in AFR 161-44.
is generally used only when maintaining an adequate
free chlorine residual in the distribution system is
(3) Other effects of chlorination. In addition to
difficult or when objectionably high levels of TTHMs
the disinfection achieved with chlorination, other
beneficial effects should be noted. Since the oxidizing
would be formed as a result of free residual chlorina-
power of chlorine is high, in the presence of free chlo-
tion. Due consideration of other TTHM control
rine, hydrogen sulfide is oxidized, nitrites are oxidized
alternatives should be made before using chloramines,
to nitrates, and soluble iron and manganese are oxi-
(see para 2-13).
(b) Breakpoint chlorination. If a water contains
dized to their insoluble oxides. Free chlorine also re-
--
acts with naturally occurring taste, odor and color-
ammonia or certain nitrogenous organic matter which
reacts with chlorine, the addition of chlorine causes
producing organic substances to form chloro-organic
2-13
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