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Science Channel
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Have you ever wondered how waste gets carried away from your home? While it may not be the most pleasant topic to think about, sewage systems are extremely important in modern society. Sewage is the mixture of waste products and water that's carried away through the underground drainage systems of pipes known as sewers. These waste products can consist of such organic and inorganic materials as human waste, garbage, mineral salts and wastes from industrial facilities.
Because the wastes in sewage often contain toxic materials and disease-causing organisms, the safe disposal of sewage is essential to any community's well-being and is one of the most important municipal services. Most sewer systems in the United States treat sewage at a treatment plant where they destroy disease-causing organisms and remove toxic substances. About 99 percent of the wastewater that enters a treatment plant comes out as treated water [source: PennState]. After treatment, the sewage is usually released into nearby waterways or the soil.
A sewage system's conduits are typically made of clay, plastic or concrete, and they're usually built so that gravity will propel waste through them. There are different types of sewers for servicing sewage from a variety of sources:
- Individual buildings deposit their sewage into collecting sewers that carry waste to a central location for treatment.
- Sanitary sewers carry only domestic sewage -- waste from commercial and residential buildings.
- Storm sewers carry runoff from melted snow and rain.
- Combined sewers carry both domestic sewage and runoff water. These sewers are not ideal because overflow from heavy rains can cause untreated sewage to be discharged from a treatment plant.
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