In wastewater treatment, what is the primary use of Sodium Bisulfite?

Sodium Bisulfite is primarily used in wastewater treatment as a chemical that effectively removes chlorine from treated wastewater. Chlorine is commonly used for disinfection, but once it has served its purpose, residual chlorine can be harmful to aquatic life if released into the environment. Sodium Bisulfite reacts with any remaining chlorine in the effluent, converting it into chloride ions that do not pose the same environmental risks. This dechlorination process is crucial for ensuring that treated wastewater meets regulatory standards before discharge into receiving water bodies.

The other options relate to processes that are important in wastewater treatment but do not accurately define the primary function of Sodium Bisulfite. For example, while adjusting pH is important, Sodium Bisulfite is not primarily used for this purpose. Similarly, aiding in coagulation is typically the role of other chemicals such as alum or ferric chloride, and disinfection is generally carried out using chlorine or other disinfectants rather than Sodium Bisulfite. Thus, the primary role of Sodium Bisulfite in wastewater treatment is dechlorination, as stated in the correct answer.