Dechlorination is performed primarily to reduce what effect when effluent is discharged into the environment?

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The main goal of dechlorination is to protect aquatic life by removing residual chlorine before the effluent enters the environment. Free chlorine residuals are highly toxic to fish and many aquatic organisms, even at low concentrations, and can cause immediate harm to gills and overall health of organisms in the receiving water. By adding a reducing agent (such as sodium bisulfite or sodium thiosulfate), the chlorine is neutralized to chloride, lowering the residual to levels that meet environmental discharge limits and minimizing harm to aquatic ecosystems.

Dechlorination does not target color, turbidity, or biochemical oxygen demand. Color comes from dissolved compounds, turbidity from suspended solids, and BOD from organic matter that biological treatment handles; none of these are the primary reason for dechlorinating effluent.