13 Water Purification: Chemical Treatment: Methods of chlorine treatment: Bleach:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
13 Water Purification: Chemical Treatment: Methods of chlorine treatment: Bleach:
Ordinary household bleach (such as Clorox) in the US contains 5.25%
sodium hypochlorite (NaOCL) and can be used to purify water if it
contains no other active ingredients, scents, or colorings. Bleach is
far from an ideal source due to its bulkiness (only 5% active
ingredient), and the instability over time of the chlorine content in
bleach. Chlorine loss is farther increased by agitation or exposure
to air. One source claims chlorine loss from a 5% solution at 10%
over 6 months if stored at 70 deg. F. Nevertheless, this may be the
only chemical means available to purify water, and it is far better
than nothing. Normal dosage is 8 drops (.4 ml) per gallon. Allow the
treated water to sit for 30 min., and if there isn't a slight chlorine
smell, retreat. Note: USP standard medicine droppers are designed to
dispense .045-.055 ml per drop. Use of other solvents or some
chemicals can change this. The dropper can be calibrated against a
graduated cylinder for greater accuracy.
Some small treatment plants in Africa produce their own sodium
hypochlorite on site from the electrolysis of brine. Power demands
range from 1.7 to 4 kWh per lb. of NaOCL. 2 to 3.5 lbs. of salt are
needed for each pound of NaOCL. These units are fairly
simple and are made in both the US and the UK. Another system,
designed for China, where the suitable raw materials were mined or
manufactured locally, used a reaction between salt, manganese dioxide,
and sulfuric acid to produce chlorine gas. The gas was then allowed
to react with slaked lime to produce a bleaching powder that could
then be used to treat water. A heat source is required to speed the
reaction up.
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