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Sewer Science

 

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Overview
Clean water is one of our most precious natural resources. Yet every time we flush a toilet, pour oil down the drain or clean with strong household chemicals, we contaminate our supply. Before wastewater can be released into our waterways, it must go through a process called sewage treatment to be decontaminated. A network of underground pipes collects the millions of gallons of waste material created by a community. When the waste and water arrive at the sewage treatment plant, large objects are filtered out with screening devices. The flow of the wastewater is then slowed to allow the sludge to settle. Oils and grease are skimmed off the surface of the effluent sewage. The effluent is then treated with chlorine to kill specific microorganisms that cause disease before the water is returned to the waterways. This process is called primary treatment. Unfortunately, this treatment only removes about 50 percent of the pollutants found in wastewater and most sewage treatment plants must use a second stage of treatment. In secondary treatment, effluent and sludge are exposed to oxygen in an aeration tank. Here, valuable microorganisms consume the organic matter and even some of the poisonous or toxic materials. Then chlorine is added before the water is released into the waterways. Sludge from both primary and secondary treatments is pumped into oxygen-free digestion tanks and then dried. This processed sludge is often used as a fertilizer or as fuel. Sludge contaminated with toxic material must be incinerated or buried in a landfill. One way or the other, water returns to the environment. That is why sewage treatment is so important.

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