Vacuum sewerage systems is low cost environmentally friendly method of transferring wastewater away from houses to treatment plants. Unlike the operation of conventional wastewater collection systems, vacuum systems base their operation in 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. Vacuum sewerage systems have been accepted with great success in over 40 countries since the 1960’s. Today there are several hundred systems installed worldwide.
A typical vacuum sewerage system consists of the following parts:
- Pumping or Vacuum Pump: 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. Once arrived in the vacuum collection tank at the vacuum station, the wastewater is pumped to the discharge point, which could be a gravity sewer or the treatment station directly. As the dwell time of the wastewater inside the system is very short and the wastewater is continuously mixed with air, the sewage is kept fresh and any fouling inside the system is avoided (less H2S).
- Vacuum network: Vacuum pipes supply the vacuum which is required by Interface valves to open and convey wastewater. A typical network consists of one or more central branches which are connected to pumping station. In order to ensure reliable transportation, the vacuum sewer line is laid in a saw-tooth (length-) profile which allows longer lengths between elevations and greater overall lift sewage. he 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 valves and sump pits: Vacuum Valves placed inside sump pits and act as ''interface'', or as a mediator between the vacuum inside pipes and the atmospheric pressure of the houses gravity sewer. 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.
The wastewater collections pits are made specifically for vacuum sewerage usage and made of polyethylene. The vacuum valve is placed in a sealed chamber which is not in contact with the wastewater. The vacuum valve opens automatically when a given amount of wastewater is collected in the sump admitting sewage and the correct amount of air and then closes. The air-water ratio ranges from 2: 1 to 5: 1.
Environmental Engineering S.A. are experts in the design, supply, installation and operation of these systems.
Vacuum Sewer Systems
The selection between a sewage vacuum systems, gravity or vacuum, is usually product of Technical-Economic Cost-Benefit Analysis. In applications with one or more of the following problems the vacuum system is particularly appropriate solution:
- Flat ground level or not quite satisfactory slope
- High water table
- Rocky ground
- Unstable soil
- Sensitive ecosystem
- Rich archaeological site
- Barriers (rivers, ditches, other pipelines)
- Sensitive Aquifer
Typical areas of Vacuum Sewerage application are the following:
- Cities and villages in almost flat areas and in areas with high water level
- Coastal and lake region and Communities
- Marinas and Ports, where the construction of gravity networks by the sea is difficult and expensive because of the high water level. Especially for Marinas relevant Directive of the European Community makes it mandatory Network installation Vacuum, to absorb the sewage of moored boats
- Railway Stations, Aircraft, Ships also use the blank for use in toilets.
- The use of vacuum toilets in houses has developed also in many countries in recent years
- The Vacuum pipes installed in shallow (up to 120cm). This eliminates the need for wide, deep ditches, and reduces the cost of excavation and environmental nuisance.
- Commonly used small pipe diameters (much smaller than the corresponding gravity networks, so construction costs are significantly lower).
- There are no sewage pits, as in gravity systems.
- Changes in the field are easily made. When obstacles are encountered, which have not been previously identified, Vacuum pipes may in most cases be driven around them.
- Since there are no leakages of liquid from the vacuum pipes, Vacuum pipes can be installed in the same trench with the pipes or water in relatively small height difference of them.
- No electricity in the valve pit.
- The uphill transport of wastewater is possible within limits (maximum allowable elevation of about 4.5m).
- The depths of the pipes can be minimized by using profiles along special design.
- The project construction time is reduced drastically because the widths and depths of the trenches is the minimum.
- Obtained large sewage flow rates, thereby reducing the risk of blockage of the pipes
- Repairing a vacuum system reduces the security measures for maintenance staff. The exposure to hazardous effluent gases collected in the pits is minimum.
- Leaks in pipes gravity may remain silent for some time, causing soil contamination. Instead, breaks in pipelines Vacuum will be identified very quickly in the control bodies of the pumping station.
- A blockage in a main gravity pipeline can cause backward flow of sewage to a number of houses. The vacuum valve isolates each home from the mains and protects backward flow.
- You only require one power source, in the Vacuum Pump Station.
- Because the infiltration of water from the soil is not feasible, the size and cost of biological treatment units is reduced.
- The mixture of air / wastewater enters the pipes at a high speed, and the air provides a pre-treatment in the wastewater in the pipe before they are passed to the ultimate recipient.