can of water, one-half of the contents of one calcium hypochlorite ampule should be
used initially as explained in a (3) above; then, additional small amounts should be
added if necessary (a (7) and (8) above). For a 55-gallon drum of water, four or five
ampules should be used initially. For a 400-gallon trailer of water, 30 ampules should
be used initially. Water, in larger containers, is not easily chlorinated by use of ampules.
The use of bulk calcium hypochlorite is described in subparagraph c, below.
c. Batch Chlorination. The term "batch chlorination" applies to the practice of
using bulk calcium hypochlorite quantities of water for which the calcium hypochlorite
ampules are not appropriate.
(1) Chlorine demand. In order to determine the required dosage, we
determine chlorine since chlorine residual equals the dosage minus the demand.
Determination of the chlorine demand requires a more accurate method of measuring
the chlorine residual than afforded by the comparator tubes in the chlorination kit. This
procedure is discussed in detail in paragraphs 2-10 and 5-10b. Briefly, it is determined
by adding a known quantity of chlorine (in ppm) to a known amount of raw water and
measuring the chlorine residual after the required contact time.
(2) Available chlorine. Calcium hypochlorite consists of 70 percent active
chlorine. Therefore, when the amount of chlorine required to provide a given residual
has been determined, that figure must be divided by 0.70 to determine the amount of
calcium hypochlorite compound required.
(3) Calculation. To determine the amount of calcium hypochlorite
necessary to provide a chlorine residual of 5 ppm-in a 3,000-gallon container of water
having a chlorine demand of 2 ppm, the following procedure should be followed:
(a) Convert the volume of water to weight:
3,000 gal water x 8.34 lbs/gal = 25,020 lbs
(b) Determine the dosage required:
Dosage = demand (2ppm) + residual (5ppm) = 7 ppm, or
7 lbs chlorine_
1,000,000 lbs water
7 lbs chlorine x lbs chlorine
X lbs chorine
1,000,000 lbs water
25,020 lbs water
= 0.175 lbs. chlorine (2.8 ounces)