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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 paper, food, grease, cigarettes, leaves, faeces, and urine. Other items that occasionally are flushed down toilets include child care-related waste (such as disposable diapers, training pants, baby wipes, bibs, pacifiers, and outgrown clothing), feminine hygiene materials (tampons and pantiliners), medical waste from hospitals, and industrial chemicals. Some items are disposed of in the sewage system for illicit purposes. Drugs are often disposed of this way in a raid, as are legitimate medications at the end of their useful life. In some prisons, inmates flush blankets down the powerful vacuum suction toilets in vain hopes of amusement caused by a clogged line. 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 apparatus and rescue apparatus for workers who must enter such spaces. A special hazard of hydrogen sulfide is that it becomes odorless at high concentrations. Another dangerous gas that can form in sewers is methane, which is both toxic and explosive.
See also Sewage treatment, landfill disposal, waste management
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