Dechlorination of Highly Chlorinated Water - Disinfection of Pipelines and Storage Facilities Field Guide - page 90

Chapter 7
Dechlorination of Highly
Chlorinated Water
Dechlorination is the practice of partially or totally removing
the chlorine residual. Highly chlorinated water used for the dis-
infection of facilities, pipelines, and appurtenances is commonly
dechlorinated when discharged. In some areas, low chlorine
residual drinking water must be dechlorinated before it can be
drained to storm sewers or directed to waterways. Water dis-
charged during pipeline break emergencies must occasionally be
dechlorinated.
Dechlorination practices generally have not been optimized to
the degree of chlorination operations. Local conditions and regu-
lations have driven the need to dechlorinate and the develop-
ment of methods that address these situations. Some of the most
important factors that need to be considered are: the flow (or vol-
ume) to be dechlorinated; the chlorine residual level (initial and
final); the time (or distance) that dechlorination must achieve;
the location and the chemistry of the water to be dechlorinated;
the impact on the receiving waterway or facility; and any regula-
tory requirements. System operators should evaluate all of the
applicable factors and select the dechlorination method that best
suits their situation.
The information provided in this chapter reflects the array of
practices currently used by water utilities to dechlorinate water
in the field. These are not the only methods but are the most
common ones. In some cases, the performance values presented
are from empirical field observations and may not predict the
performance of a practice used in another situation. Operators
should test any dechlorination procedure to determine the exact
conditions for that application.
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