Vacuum sewer

A vacuum sewer system is a method of transporting sewage from its source to a sewage treatment plant. It uses the difference between atmospheric pressure and a partial vacuum maintained in the piping network and vacuum station collection vessel. This differential pressure allows a central vacuum station to collect the wastewater of several thousand individual homes, depending on terrain and the local situation. Vacuum sanitary sewers take advantage of available natural slope and are most economical in flat sandy soils with high ground water.

Vacuum sewers were first installed in Europe in 1882. The first applied use of negative pressure drainage (so called vacuum sewerage) was the Dutch engineer Charles Liernur in the second half of the 19th century. Technical implementations of vacuum sewerage systems were started after 1959 in Sweden. Until the last 30 years it had been relegated to a niche market, although it has remained in use on trains and airplanes. Nowadays several system suppliers offer a wide range of products for many applications.

The main components of a vacuum sewer system are a collection chambers and vacuum valve parts, sewers, a central vacuum station and monitoring and control components.

Vacuum technology is based on differential air pressure. Rotary vane vacuum pumps generate an operation pressure of -0.4 to -0.6 bar at the vacuum station, which is also the only element of the vacuum sewerage system that must be supplied with electricity. Interface valves, that are installed inside the collection chambers, work pneumatically. Sewage flows by means of gravity from each house into a collection sump that might collect sewage from 2-6 houses and is located in public area. After a certain fill level inside this sump is reached, the interface valve opens. The impulse to open the valve is usually transferred by a pneumatically (pneumatic pressure created by fill level) controlled controller unit. No electricity is needed to open or close the valve. The energy is provided by the vacuum itself. While the valve is open, the resulting differential pressure between atmosphere and vacuum becomes the driving force and transports the wastewater towards the vacuum station. Besides these collection chambers, no other manholes, neither for changes in direction, nor for inspection or connection of branch lines, are necessary. High flow velocities keep the system free of any blockages or sedimentation.

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Wikipedia