Sewage system
Sewerage is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater). It encompasses components such as receiving drains, manholes, pumping stations, storm overflows, and screening chambers of the combined sewer or sanitary sewer. Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment. It is the system of pipes, chambers, manholes, etc. that conveys the sewage or storm water.
According to this definition, sewerage and sewage are two different terms. However, at least in American English colloquial usage, both terms are sometimes used interchangeably.
The main part of a sewerage system is made up of large pipes (i.e. the sewers, or "sanitary sewers") that convey the sewage from the point of production to the point of treatment.
Types of sanitary sewer systems include:
Sewerage systems often reduce the water table in areas, especially in densely populated areas where rainwater (from house roofs) is directly piped into the sewerage system as opposed to being simply allowed to be absorbed by the soil. In certain areas it has resulted in a significant lowering of the water table. In the example of Belgium, a lowering of the water table by 100 meters has been the result. The freshwater that is accumulated by the sewerage system is then piped to the sea.
In areas where this is a concern, vacuum sewers may be used instead due to the shallow excavation that is possible for them.
Severe constraints are applied to sewerage, which may result in premature deterioration. These include root intrusion, joint displacement, cracks and holes formation leading to a significant volume of leakage with an overall risk for the environment and public health. For example, it is estimated that 500 million m3 of contaminated water per year can leak into soil and ground-water in Germany. The rehabilitation and replacement of damaged sewers is very costly. Annual rehabilitation costs for Los Angeles County are about €400 million, and in Germany, these costs are estimated to be €100 million.
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