This document summarizes the journey of wastewater from homes through treatment plants before being returned to the environment. It explains that wastewater is collected through sewer systems and sent by gravity to local treatment plants. These plants treat wastewater in three levels - primary removal of solids, secondary aerobic biological treatment to reduce organic matter and nutrients, and tertiary advanced nutrient removal. After treatment, effluent is returned to streams while sludge is used or disposed of as fertilizer, fuel after drying, or composted.