Dilution is the most common means of detoxification of treated water.
The use of activated carbon filters allows removal of chlorine without replacement with another salt, and this is the most effective means of actual dechlorination (Menis-Croxall and deBruyn 1997).
Where chlorine dosage is at high concentrations or relatively frequent, dechlorination may be required to meet discharge regulations, unless outflow is to a storage lagoon or is diluted to acceptable levels. Dechlorination can be done by addition of sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), sodium metabisulfite (Na2S2O5), or sulfur dioxide (SO2) (Barton 1993; Claudi and Mackie 1994). Sodium bisulfite in solution, known as liquid sulfite, is commonly used at 1.8 to 2.0 mg L-1 of sulfite per mg L-1 of residual chlorine, and can be fed into the discharge waters at any time as it acts rapidly (Claudi and Mackie 1994).
Zebra Mussel Chemical Control Guide
Hypochlorite and Chlorine Gas