What is the main reason for adding sodium hypochlorite to sewers?

Sodium hypochlorite is commonly added to sewers primarily to control Biological Oxygen Demand (BOD). BOD is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in the water. By adding sodium hypochlorite, which acts as a disinfectant and oxidizing agent, it helps reduce the levels of organic materials and harmful pathogens in the sewage. This is critically important in maintaining the overall health of the wastewater collection system and ensuring compliance with environmental regulations. Effective BOD control can significantly improve the treatment process and reduce the environmental impact of wastewater discharge.

The other options, while they may touch on issues related to wastewater management, do not accurately reflect the primary purpose of sodium hypochlorite in sewer systems. The focus on BOD showcases the chemical's role in promoting better water quality and supporting effective treatment processes.