Which two chemicals are typically used to de-chlorinate water?

De-chlorination is the process of removing chlorine from wastewater or treated water, and it's essential to prevent harm to aquatic life when discharging effluent into water bodies. Among the chemicals mentioned, sulfur dioxide and sodium bisulfite are both effective agents used for this purpose.

Sulfur dioxide functions by reacting with chlorine to form sulfate, effectively neutralizing the chlorine. Sodium bisulfite, likewise, serves as a reducing agent, which can also convert chlorine into chloride ions. Both of these chemicals are well-regarded in water treatment for their ability to quickly and effectively reduce chlorine concentrations to non-toxic levels.

The other options do not serve the purpose of de-chlorination successfully. Specifically, chlorine and ammonia are components used in disinfection processes, while sodium bicarbonate and hydrogen peroxide do not have the direct capability of de-chlorination. Lastly, calcium carbonate and sodium chloride do not remove chlorine from water; they are used more commonly for other purposes such as pH adjustment and salinity, respectively. Thus, sulfur dioxide and sodium bisulfite are identified as the correct choices for de-chlorination in wastewater treatment.