vacuum sewage

vacuum sewage systems

Manufacturers and suppliers:
Europe North and South America Asia Pacific

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 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 J.Lilijendahl and afterwards brought on the market by the Electrolux where QUA-VAC took over the vacuum sewer technology and Electrolux concentrated on the vacuum toilets for ships only.

A vacuum sewer uses the differential pressure between atmospheric pressure and a partial vacuum maintained in the piping network and Vacuum station tank. This vacuum differential pressure allows a central vacuum station to collect up to 1500 individual homes depending on terrain. Vacuum sewers take advantage of available slope in the terrain and are most economical in flat sandy soils with high ground water.

Collection chambers and vacuum valve units
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 chamber work pneumatically. Sewage flows by gravity into each house's collection sump. After a certain level is reached, the interface valve that is controlled by a controller will be opened. The resulting differential pressure between atmosphere and vacuum becomes the driving force, and transports the wastewater towards the vacuum station. Therefore, no inspection manholes are required in vacuum systems!

Vacuum sewer lines
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 - they should never be totally filled with sewage since the hydraulic friction loss would be too high! This is guaranteed when using suitable interface valves. For an investor, it must be paid attention to the fact that the choice of equipment ensures the automatic optimisation of the air-to-liquid ratio.
Considering that the vacuum idea relies on external energy for the transport of fluids, sewers can be laid in flat terrain and up to certain limits may also be counter-sloped. The saw-tooth profile keeps sewer lines shallow, lifts minimise trench depth (approx. 1.0 - 1.2 m). In this depth, expensive trenching, as it is the case for gravity sewers with the necessity to install continuously falling slopes of at least 0.5%, is avoided.

Central vacuum station
Once arrived in the vacuum storage tank (underground) at the vacuum station, sewage is pumped to the discharge point, which could be a gravity sewer or the treatment station directly.

Advantages

closed, pneumatically controlled system with a central vacuum station. Electrical energy is only needed at this centraal station
no sedimentation due to self-cleansing high velocities
spooling and maintenance of the sewer lines is not necessary
manholes are not required
no pumping stations required
investment costs can be reduced up to 50 % due to simple trenching at shallow depths, close to surface
flexibility of piping, obstacles (as open channels) can be over- or underpassed
reduced installation time
small diameter sewer pipes of HDPE , PVC materials; savings of material costs
aeration of sewage, less development of H2S, with its dangers for workers, inhabitants, as well as corrosion of the pipes may be avoided; sewage is kept fresh
no odours along the closed vacuum sewers
no infiltration, less hydraulic load at treatment station and discharge sewers
absolutely no leakages (vacuum avoids exfiltration)
sewers may be laid in the same trench with other mains, also with potable water or storm-water, as well as in water protection areas

Limitations

vacuum systems are not capable of transporting sewage over very long distances (> 3-4 km)
vacuum sewerage systems are only capable for the collection of wastewater within a separated system and not for the collection of storm-water
the lines can only reach up to 3-4 km laid in flat area
restrictions of the system due to headlosses (3-4 m)
systems should be designed with help of an experienced manufacturer (usual free of charge)
external energy is required at a centraal point for collecting sewage
odours close to the vacuum station can occur, biofiltre eventually necessary

Application Fields

Vacuum sewer systems becomes more and more the preferred system in the case of particular circumstances:

Especially difficult situations as ribbon, peripheral settlements on flat terrain with high specific canal lengths of longer than 4 metres per inhabitant are predestined for the application of vacuum sewerage systems. In the case of sparse population density the influence of the costs for the collection chambers and vacuum stations are less important in comparison to the costs of long and deep sewers on gravity. Missing incline of the ground, unfavourable soil (rocky or swampy grounds) and high groundwater table (with the necessity of dewatering trenches) lead to enormous investment costs in regards to gravity sewerage systems. On the contrary vacuum sewers that are small in diameter can be laid close to the surface in small trenches. Vacuum sewers can pass through water protection areas and areas with sensitive high ground water tables, because there is no danger of spoiling groundwater resources (vacuum sewers have a high leaktightness due to their material; moreover the vacuum itself does not allow exfiltration). Vacuum systems has also been applied to collect toxic wastewater. In seasonal settlements (recreation areas, camping sites etc.) with conventional gravity sewer systems, sedimentation problems can easily occur as automatic spooling from the daily waste water does not take place. High flow velocities within vacuum sewers prevent such sedimentation problems. Even in old narrow and historical villages, the use of vacuum sewer systems becomes more and more important due to a fast (traffic, tourism), cost-effective and flexible installation.

The county of Sarasota, Florida[1] and the city of Carnation, Washington[2] are developing a county wide collection system and is incorporating vacuum sewers.

In Germany, several hundred well-working systems are operating since the 1970's. Especially in the Middle East, vacuum sewer systems become more and more important due to easy and fast installation along with water saving effects and easiness of maintenance.

The world most famous vacuum sewer project is currently the Palm Island Jumeirah, located in in front of the coast of Dubai City, United Arab Emirates. Approx. 23.000 people will be connected to this vacuum sewer system with only 1 central vacuum station once the Palm Island has been completely finished. Others are Amwaj Island in Bahrain serving more than 15.500 with a vacuum sewer system and running for more than 3 years.

The biggest installation in Europe and supposed to be the largest vacuum sewer system world wide can be found in Gerasdorf (near Vienna), Austria, where many benefits of a vacuum sewer system helped to overcome difficult conditions in this mountainous area.

Good examples can be found on the Maldives, the post-tsunami WATSAN project UNICEF - UN, where on several islands vacuum sewer system was the best option. Several other project, mainly for resorts, have already been realized on the Maldives.