Water Q&A: Where does our home wastewater go?

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Learn what happens at a wastewater treatment plant.

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Where does our home wastewater go?

Water Questions and Answers

Water leaving our homes generally goes either into a septic tank in the back yard where it seeps back into the ground, or is sent to a wastewater-treatment plant through a sewer system.

Different treatment is used depending on the type of water coming into the plant and the water-quality requirements of water leaving the plant. Often the first stages of water treatment are purely physical methods, such as letting solid particles settle to the bottom of a holding tank and filtering the water through sand or other fine particulate matter. Filters are used to screen out large particles, and at a minimum, chlorine is added to kill dangerous bacteria and microorganisms.

A typical set of steps to treat water:

  • Odor control: Chemicals can help keep down foul odors
  • Screening: Move water through screens to separate larger solids and trash
  • Primary treatment: Move water into large tanks and allow solid material to settle at the surface. Scrape material off and dispose of it
  • Aeration: Stir up the water to get it to release gasses, and pump air through the water to allow bacteria to act on organic matter to help it decay.
  • Remove sludge: Solid material settles to the bottom and removed
  • More filtration: Filter water through sand, for example, to reduce bacteria, odors, iron, and other solids.
  • "Digest" the solid material: Hold and heat the solid material to break it down to nutrient-rich biosolids and methane gas
  • Disinfection: Water is treated with chlorine to kill bacteria
Aerial view of a wastewater-treatment plant

Wastewater treatment plants can treat sewage and create water that can be used for other purposes (relaimed wastewater). (Credit: Michal Jarmoluk. Pixabay Creative Commons)

Some systems have additional water treatment that use biologic processes to remove organics, nitrogen, and phosphorus, a membrane tank to remove bacteria and suspended solids, ultraviolet disinfection to render viruses inactive, and aeration to raise the oxygen level (needed by fish living in the river where the treated wastewater is dumped after cleansing).