Dechlorination of Highly Chlorinated Water - Disinfection of Pipelines and Storage Facilities Field Guide - page 101

water through the tubes to assure good contact between the
water and dechlorination tablets. As the stream of water flows
past the feed tubes containing dechlorination tablets, the dechlo-
rination agent is released into the water by dissolution. Commer-
cial tablet dispensers are available for a wide variety of flow
rates and chlorine concentrations.

Flow Control Measures
During planned and unplanned water releases, it may be
necessary to construct flow control measures to prevent the
water from entering directly into a water body and to provide an
opportunity for better mixing of the dechlorinating agent.
Construction of berms, swales, ditches, or redirection pipes are
common methods used to control the flow of released water.

Chemical Dechlorination Calculation
Table 7-5 lists the amount of dechlorination chemical needed
to remove 1 mg/L residual for 100,000 gal or 100 m 3 . The volume
of water is calculated from Table 3-6 for pipelines, and Table 5-2
and calculators c5-1, 5-2, 5-3, and 5-4 for storage tanks. Make sure
that the volumes are in gallons for US units and cubic meters for
SI units. The total amount of dechlorination chemical needed is
calculated using the dechlorination chemical calculator .

Table 7-5 Approximate dechlorination chemical needed for fixed volume

Pounds of Chemical Needed for 100,000 gal per 1 mg/L

Sodium
Thiosulfate

Sodium
Bisulfite

Sodium
Metabisulfite

Sodium
Sulfite

Calcium
Thiosulfate

Ascorbic
Acid

Sodium
Ascorbate

1.58 1.34 1.23 1.63 1.02 2.08 2.33

Kilograms of Chemical Needed for 100 m 3 per 1 mg/L

Sodium
Thiosulfate

Sodium
Bisulfite

Sodium
Metabisulfite

Sodium
Sulfite

Calcium
Thiosulfate

Ascorbic
Acid

Sodium
Ascorbate

0.19 0.16 0.15 0.20 0.12 0.25 0.28