What is a Sewage System?

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  • Written By: M. McGee
  • Edited By: Jenn Walker
  • Last Modified Date: 05 November 2019
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A sewage system moves waste water and materials away from their origin point so they may be disposed of or treated. There are three main varieties of modern sewer systems. Cities often have two types of systems, the storm sewer, which moves clean water and refuse, and the effluent sewer which moves dirty water and human waste. In areas where buildings aren’t connected to a city system there is the third type of sewage system, the septic tank. This moves sewage away from the home where it breaks down overtime.

Sewage systems rose with the invention of cities. As a result, there are records of sewage systems going back almost 5,000 years. While most of these early systems were rudimentary by modern standards, some of these systems are still in operation. The oldest sewage system still in use is nearly 3,000 years old. This case is an exception rather than the norm, and most sewer systems are no more than 200 years old.

Most cities use two unconnected sewer systems, the storm sewer and the effluent sewer. Storm sewers collect rainwater and other clean waters. These sewers have the drainage grates commonly seen on city streets. This system typically contains street refuse and dirt, but no actual sewage. In many case, cities simply filter this water to remove any garbage or refuse and allow it to drain, untreated, into a local water source. Since the water is clean, this will typically have no environmental impact.


The other type of sewer system is for effluent. This is the actual municipal sewage system. This system collects human waste and wastewater from homes and business and pumps it to a treatment facility. This facility filters the water, removing solid substances such as human waste and garbage. The water and solids go through various processes where the harmful microorganisms within the substances are removed, killed or consumed. Once the water’s level of harmful bacteria is back to natural levels, the water is allowed back into the local system.

The third common sewage system is a septic tank. This type of system is found in location were there isn’t an available hookup to a city system. With a septic tank, sewage is moved a short distance from the building and held in a tank. The solids float to the bottom and are digested by specialized organisms in the tank. The remaining liquid, now much cleaner, drains out into the surrounding land. Once there, natural processes remove the rest of the waste before the water returns to the local system.


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