Vacuum Stations


KLWTD Collections Staff

Introduction

Closed “Green” System: Because vacuum sewers are completely contained, there is no danger of sewage escaping into the environment.

Reliable System: The AIRVAC system will continue to function normally during a power outage with power from a standby generator located at the vacuum station.

Minimal Construction Impact: Vacuum sewers use small diameter vacuum mains buried in shallow trenches. That means less digging, smaller equipment, and little disruption to yards and traffic.

Vacuum sewers were first installed in Europe in 1882 but until the last 30 years it had been relegated to a niche market. The first who has applied the negative pressure drainage (so called vacuum sewerage) was the Dutch engineer Charles Liernur in the second half of the 19th century. It was only used on ships, trains and airplanes for a long time. Technical implementations of vacuum sewerage systems were started after 1959 in Sweden by Joel Liljendahl and afterwards brought onto the market by Electrolux. Nowadays several system suppliers offer a wide range of products for many applications.

How It Works

A vacuum sewer system uses the differential pressure 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 sewers take advantage of available natural slope in the terrain and are most economical in flat sandy soils with high ground water.A vacuum sewer system uses the differential pressure 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 sewers take advantage of available natural slope in the terrain and are most economical in flat sandy soils with high ground water.

Technology

Vacuum Tank

In order to ensure reliable transport, the vacuum sewer line is laid in a saw-tooth (length-) profile, which will be referred to more precisely afterwards. The whole vacuum sewers are filled with air at a pressure of -0.4 to -0.6 bar. The most important aspect for a reliable operation is the air-to-liquid ratio. When a system is well designed, the sewers contain only very small amounts of sewage. The air-to-liquid ratio is usually maintained by “intelligent” controller units or valves that adjust their opening times according to the pressure in the system.

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. Any sewage flows by means of gravity into each house’s collection sump. After a certain fill level inside this sump is reached, the interface valve will open. 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 according 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.

Vacuum Station

Vacuum sewer systems are considered to be free of ex- and infiltration which allows the usage even in water protection areas. For this reason, vacuum sewer lines may even be laid in the same trench as potable water lines (depending on local guidelines). The system supplier should certify his product to be used in that way. To achieve the condition of an infiltration-free system and therefore allowing to reduce the waste water amounts that need to be treated, water tight (PE material or similar) collection chambers should be used. Valve and collection sump (waste water) preferably should be physically separated (different chambers) in order to protect service personal against direct contact with waste water and to ensure longer life cycles (waste water is considered to be corrosive).

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