12 Water Purification: Chemical Treatment: Chlorine:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
12 Water Purification: Chemical Treatment: Chlorine:
Chlorine is familiar to most Americans as it is used to
treat virtually all municipal water systems in the United States. For
a long time chlorine, in the form of Halazone tablets, was used to
purify small batches of water for campers and military troops. Later
questions emerged about the effectiveness of Halazone, and in 1989,
Abbot labs pulled it off the market. If Halazone Tablets are
encountered outside the US, the nominal shelf like is 6 months, and
the dosage is 2 tabs per liter. Until recently, there was no chlorine
product designed for wilderness/survival use available in the US.
Chlorine has a number of problem when used for field treatment of
water. When chlorine reacts with organic material, it attaches itself
to nitrogen containing compounds (ammonium ions and amino acids),
leaving less free chlorine to continue disinfection. Carcinogenic
trihalomethanes are also produced, though this is only a problem with
long term exposure. Trihalomethanes can also be filtered out with a
charcoal filter, though it is more efficient to use the same filter to
remove organics before the water is chlorinated. Unless free chlorine
is measured, disinfection can not be guaranteed with
moderate doses of chlorine. One solution is superchlorination, the
addition of far more chlorine than is needed. This must again be
filtered through activated charcoal to remove the large amounts of
chlorine, or hydrogen peroxide can be added to drive the chlorine off.
Either way there is no residual chlorine left to prevent
recontamination. This isn't a problem if the water is to be used at
once.
Chlorine is sensitive to both the pH and temperature of the treated
water, Temperature slows the reaction for any chemical treatment, but
chlorine treatment is particularly susceptible to variations in the pH
as at lower pHs, hypochlorous acid is formed, while at
higher pHs, it will tend to dissociate into hydrogen and chlorite
ions, which are less effective as a disinfectant. As a result,
chlorine effectiveness drops off when the pH is greater than 8
Chlorine, like iodine, will not kill Cryptosporidia.
Continue to:
My Books
