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Sewage is domestic, municipal, or industrial liquid waste products. How it is disposed varies by the area, and the local commitment to the environment. In some countries, notably the United States, national law mandates sanitary treatment of sewage, and outfalls are regulated. Surprisingly, many quite wealthy countries have untreated outfalls directly to surface water, often causing disease, pollution and undrinkable tapwater.

Sewage may be carried directly through pipelines to outfalls, or from upstream sources via river systems. Sewage is often from storm water runoff of streets, parking lots, lawns and commercial and industrial areas. In some urban areas, sewage is carried separately in sanitary sewers while runoff from streets is carried in storm drains. Access to either of these is typically through a manhole.

Sewage may drain directly into major watersheds with minimal or no treatment. When untreated, sewage can have serious impacts on the quality of an environment and on the health of people. Pathogens can cause a variety of illnesses. Some chemicals pose risks even at very low concentrations and can remain a threat for long periods of time because of bioaccumulation in animal or human tissue.

The solution, of course, is sewage treatment.

Composition of sewage

Sewage contains mineral, animal and vegetable matter in suspension, as well as large numbers of bacteria. It may contain for example paper, food, grease, cigarettes, leaves. Sewage odors are unacceptable to most people. In a confined space such as a manhole or lift station housing, gases such as hydrogen sulfide may be concentrated to dangerous levels, requiring special breathing and rescue apparatus for workers who must enter such spaces. A special hazard of this gas is that it actually becomes odorless at high concentrations.

See also Sewage treatment, landfill disposal, waste management