Which of the following is most commonly used for dechlorination in wastewater treatment?

The most commonly used method for dechlorination in wastewater treatment involves sulfur dioxide. This compound is favored because it effectively neutralizes chlorine, which is often used in disinfection processes. When sulfur dioxide is introduced to chlorinated water, it reacts with chlorine to form soluble chlorosulfates and other harmless products, thereby removing harmful chlorine from the water before it is released into the environment.

Sulfur dioxide's practicality in field applications enhances its preference in various wastewater treatment facilities. It operates efficiently at a wide range of pH levels and is less toxic to aquatic life compared to remaining chlorine concentrations, making it a suitable choice for ensuring water quality.

Hydrochloric acid, on the other hand, is primarily utilized to adjust pH levels rather than for dechlorination. Chlorine gas is not suitable for dechlorination as it serves the opposite purpose; it's a disinfectant used to kill pathogens. Hydrogen peroxide is also capable of dechlorination, but its use is not as common or straightforward due to costs and handling precautions compared to sulfur dioxide, which provides a more effective and economical solution.