What chemicals are utilized to remove chlorine from treated wastewater before it is released into the environment?

The process of removing chlorine from treated wastewater is essential to prevent harmful effects on aquatic life and the environment when the water is released back into natural bodies. Sodium bisulfite and sulfur dioxide are commonly utilized for this purpose because they act as effective dechlorinating agents.

Sodium bisulfite is a reducing agent that reacts with chlorine, effectively neutralizing it and converting it into harmless chloride ions. This reaction allows for the safe removal of chlorine, ensuring that the treated water meets environmental discharge standards. Similarly, sulfur dioxide also acts as a dechlorinator and is often used in larger treatment facilities due to its effectiveness and lower cost compared to some other chemicals.

The other options provided do not serve the primary function of dechlorination. Chlorine gas and bleach are forms of chlorine, which would only add to the chlorine content rather than remove it. Calcium sulfate and ferric chloride are not used for dechlorination; rather, ferric chloride may serve in coagulation processes in water treatment. Sodium hydroxide and alum are typically used for pH adjustment and coagulation and do not play a role in removing chlorine from wastewater.