What is the primary purpose of adding sodium hypochlorite to sewers?

The primary purpose of adding sodium hypochlorite to sewers is to control odors. Sodium hypochlorite is a powerful oxidizing agent and disinfectant, which helps to reduce the concentration of hydrogen sulfide gas and other compounds that can lead to unpleasant smells in the sewer system. When introduced to the wastewater, it reacts with the odor-causing substances, neutralizing them, and thus significantly improves the overall smell and air quality in the vicinity of the sewer system.

The other options, while relevant to wastewater treatment, do not accurately describe the main function of sodium hypochlorite. For instance, while it may have some influence on waste decomposition, this is not its primary use. Its role in enhancing pipe integrity is also not applicable, as sodium hypochlorite can potentially lead to material degradation over time if not managed properly. Promoting bacterial growth is contrary to the intended use of sodium hypochlorite, as its disinfectant properties tend to reduce bacterial populations rather than enhance them.