Why is the removal of nutrients (nitrogen and phosphorus) important in sewage treatment?

The removal of nutrients such as nitrogen and phosphorus during sewage treatment is crucial primarily because it helps to prevent eutrophication in receiving water bodies. Eutrophication is a process where excessive nutrients, particularly phosphorus and nitrogen, enter a water body and stimulate the overgrowth of algae. This rapid algal bloom can deplete oxygen levels in the water and harm aquatic life, leading to dead zones where fish and other organisms cannot survive.

By effectively removing these nutrients during the sewage treatment process, facilities can significantly reduce the likelihood of eutrophication occurring in lakes, rivers, and coastal areas. This not only preserves aquatic ecosystems but also helps maintain the quality of water used for recreational purposes and drinking water sources.

While enhancing flavor, reducing treatment costs, and improving clarity may be benefits in certain contexts, they are secondary to the critical environmental impact of preventing eutrophication. Cleaning water by removing excess nutrients directly addresses one of the main challenges in water quality management, making option B the most important and relevant reason for nutrient removal in sewage treatment.