What is a common requirement of NPDES permits regarding wastewater treatment?

NPDES (National Pollutant Discharge Elimination System) permits are designed to regulate the discharge of pollutants into the waters of the United States. A common requirement of these permits is the removal of both phosphorus and nitrogen from wastewater before it is released into the environment. This is crucial because excess phosphorus and nitrogen can lead to nutrient pollution, which causes algal blooms and other detrimental environmental impacts such as hypoxia in aquatic ecosystems.

Phosphorus and nitrogen are essential nutrients for plant growth, but when they enter water bodies in excessive amounts, they can disrupt the natural balance, leading to overgrowth of algae and degrading water quality. By including requirements for the removal of these nutrients, NPDES permits aim to protect water quality and aquatic life.

The other options focus on more specific or limited aspects of wastewater treatment that do not encompass the comprehensive approach often mandated by NPDES permits regarding nutrient control.