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Where does our home wastewater go?

Aerial view of the state of the art Johns Creek treatment plant in Atlanta, Georgia">
Credit: Aerial Innovations of Georgia

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 sewage-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.

Some systems have additional water treatment, such as adding chemicals to make matter bunch up (flocculate) and fall out of solution and adding chemicals to make the water less corrosive to metal. Other more advanced methods are sometimes used 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).