Vacuum Sewer Systems
A vacuum sewer moves wastewater with atmospheric pressure instead of gravity. Small, shallow pipes held under vacuum suck sewage from collection chambers to a central station, which makes them ideal for flat land, high groundwater, rock and coastal areas.
How it works
Wastewater from each building flows by gravity into a small collection chamber. When the level rises, a pneumatic interface valve opens for a few seconds. The pressure difference between the atmosphere and the vacuum main pushes a slug of sewage, followed by air, into the pipe at high speed. Sawtooth "lifts" in the pipe profile let the system climb gentle slopes. At the vacuum station the sewage collects in a tank and is pumped on to the treatment plant.
Pressures
The vacuum station typically holds the mains at about −0.5 to −0.7 bar relative to atmosphere, which is 0.3–0.5 bar absolute. That is a rough vacuum: water there still boils only at about 70–77 °C, so the sewage stays liquid.
Advantages and limits
Compared with gravity sewers:
- Small pipes laid shallow in narrow trenches, without deep excavation or lift stations.
- No exfiltration: a leak lets air in, not sewage out.
- High flow velocity keeps pipes clean.
- Needs power at the vacuum station and regular valve maintenance.
Typical pressures
| Process stage | Pressure |
|---|---|
| Vacuum mains (typical) | −0.5 to −0.7 bar gauge (0.3–0.5 bar abs) |
| Vacuum toilets (trains, aircraft, ships) | Similar rough vacuum |
Suitable vacuum pumps
References & further reading
- K. Jousten (ed.). Handbook of Vacuum Technology, 2nd ed.. Wiley-VCH (2016). Standard reference on gas flow, conductance, pumps and gauges.
- J. F. O’Hanlon & T. A. Gessert. A User’s Guide to Vacuum Technology, 4th ed.. Wiley (2023). Practical design of vacuum systems, pump-down and outgassing.
Frequently asked questions
How deep is the vacuum in a vacuum sewer?
About −0.5 to −0.7 bar relative to atmosphere, which is 0.3–0.5 bar absolute, a rough vacuum well within the range of rotary vane or claw pumps.
Where are vacuum sewers used?
In flat, coastal or rocky terrain, areas with high groundwater, holiday resorts and new developments where deep gravity sewers would be expensive, and in vacuum toilets on trains, aircraft and ships.
What happens if a vacuum sewer pipe leaks?
Air is drawn into the pipe instead of sewage escaping, so groundwater is protected. The vacuum station sees the extra air load and runs longer, which helps locate the leak.
Other applications
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