DISINFECTION OF WATER
Section I. PRINCIPLES OF DISINFECTION
Disinfection is the destruction of pathogenic (disease-producing)
microorganisms. It is essential in the purification process of military water treatment.
Disinfection is always included in military water purification because the other three
steps--coagulation, sedimentation, and filtration--cannot be relied upon to remove all
pathogenic microorganisms from water. Even when the water comes from a very safe
source (such as a deep well) and requires no other treatment, disinfection is always
practiced to protect against possible contamination or recontamination during handling.
Every disinfectant or means of disinfection should satisfy certain criteria. The
a. Must contact all particles of the water treated.
b. Must be effective for a wide range of expected changes in the conditions of
treatment or in the characteristics of the water being treated.
c. Must be nontoxic to humans at the concentration levels present in the finished
d. Must have a residual action sufficient to protect the distribution system from
bacterial growths and be measurable. For example: with chlorine residual action must
be at least 5.0 ppm after 30 minutes).
e. Must be of a practical method.
CHLORINE AS A DISINFECTANT
When calcium hypochlorite (Ca(CIO)2) is dissolved in water, the chlorine goes
into solution and the calcium settles out in the form of a sludge consisting of calcium
carbonate (CaCO3), calcium hydroxide (Ca(OH)2), or both, depending upon the
carbonate content of the water. The chlorine is present in solution as hypochlorous acid
(HOCI) or free hypochlorite ion (CIO-), depending on the pH. Both HCIO and CIO- are
powerful oxidizing substances and the available chlorine in either of these two forms
rapidly oxidizes both organic and inorganic substances in the water, including bacteria.
The chlorine used in this reaction is converted to chloride and is no longer available as