What happens after wastewater leaves a building?

Water leaving a building can carry scraps, suspended solids and organic material from living things. A wastewater plant removes some material by separation and changes some through living processes. Visible dirt is only part of what the water carries.

First, screens catch large objects that could block or damage later equipment. In settling tanks, water moves slowly enough for some heavier suspended material to sink. Taking out a large scrap and taking out a sinking particle are physical separations: the material has moved out of the water route.

Biological treatment handles material that a screen cannot simply catch. Microorganisms, including bacteria, use some organic matter as food. They transform it as they grow and carry out life processes. Many systems supply air so oxygen-using microbes can do this work. Microbial growth can later be separated from the water too.

Caught scraps, settled material and microbial solids still need their own treatment and management. Water may receive more treatment, including germ control, before release or reuse. These routes handle material in different ways; treated wastewater is not automatically drinking water.