Dechlorination of Highly Chlorinated Water - Disinfection of Pipelines and Storage Facilities Field Guide - page 94

Table 7-2 Comparison of dechlorination agents

Dose at
pH 7.0
mg/mg Cl *

pH of
1%
Solution

Forms
Available

Decomposition/
Off-gassing

Oxygen
Scavenger Agent

Sodium
bisulfite

Powder/
crystal

1.61 4.3 Sulfur dioxide Strong

Sodium
metabisulfite

Powder/
crystal

1.47 4.3 Sulfur dioxide Strong

Sodium
sulfite

Powder/
crystal/
tablet

1.96 8.5-10.0 Sulfur dioxide Moderate

Sodium
thiosulfate

Powder/
crystal

1.9 7.0 Sulfur dioxide Weak

Calcium
thiosulfate

Powder/
crystal

1.22 6.5-7.0 Sulfur dioxide Weak

Ascorbic
acid

Powder/
crystal/
tablet

2.5 6.0* none None

reported

Sodium
ascorbate

Crystal/
tablet

2.8 7.0 none None

reported

* All dechlorination dosage estimates listed are based on field results (values may differ
based on variable conditions). Dechlorination capacity must be checked for each
application using site-specific conditions. The symbol Cl in this heading refers to
chlorine as hypochlorous acid (HOCl).

Table
Tamer

This table shows the approximate dosage of various
dechlorination chemicals needed to neutralize one
milligram of chlorine. Example: About 1.61 mg of sodium
bisulfite is needed for each milligram of chlorine.

The discharge spigot on the container can be adjusted to provide
a minimum dechlorinating solution feed rate into the water flow,
based on calculations involving the concentration of the dechlori-
nating solution, water flow rate, and residual chlorine concentra-
tion in the flow stream.
To minimize the volumes of dechlorinating solution needed on
field vehicles, wherever possible, dry dechlorinating agent should