Disinfection of Pipelines - Disinfection of Pipelines and Storage Facilities Field Guide - page 50

11. High calcium hypochlorite concentrations (greater than
100 mg/L) may raise the pH of the water to unacceptable
levels. Measure the pH of the chlorinated water to ensure
that optimum pH is maintained. Remember that if the
pH is greater than 10, virtually all of the chlorine resid-
ual is present as hypochlorite ion, which is a less effective
disinfectant than hypochlorous acid.
Chlorine amount calculation. The following tables and
calculators should be used to determine the amount of chlorine
and the application circumstances to correctly perform the slug
method of pipeline chlorination. A section of the pipeline is filled
with 100 mg/L chlorine water (the slug), and this portion is
moved along the length of the pipe so that there is a 3-hr contact
at every point. The size of the slug and the rate of movement are
critical to the success of this method.
The chlorinator feed settings needed to produce a 100 mg/L
dosage at various flow rates are given in Table 3-10. These settings
are not exact but should yield a dosage suitable for field applica-
tions. The flow rate given in the left column is the “fill rate” of the
pipeline. So, if the pipeline is being filled at 20 gpm, the chlorina-
tor should be set at 24 lb/day to produce a 100 mg/L slug. Using
SI units, if the pipeline is being filled at 2 L/sec, the chlorinator
should be set at 720 grams/hr.
Table 3-11 lists the feed rate needed to prepare a 100 mg/L
dosage slug using sodium hypochlorite solutions. The feed rate is
matched with the pipeline feed (or fill) rate. From the table, if the
pipeline is being filled at 25 gpm, the feed rate of a 1% sodium
hypochlorite solution must be about 15 gallons/hr.
The amount of calcium hypochlorite needed to produce a
100 mg/L dosage for each 500 ft of pipeline is given in Table 3-12.
The amount is listed in ounces (pounds), grams (kilograms), and
the number of 5-gram tablets. Tablets are generally not used for
this method since a large number is usually needed. It is common
to use calcium hypochlorite to prepare 1% or 5% chlorine solu-
tions to produce the slug as shown in Table 3-11. A 1% solution is
prepared by mixing 1 pound of calcium hypochlorite (65%
strength) in 8 gallons of water.