Pressure drainage
Various systems for wastewater disposal are referred to as pressure drainage :
- Special drainage systems serve to discharge the wastewater (dirty, rain and extraneous water) that occurs in structural systems by means of overpressure or underpressure . In contrast to traditional, pressureless gravity drainage via gravity sewers , these are still of little importance.
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Vacuum drainage
- from flat roofs and other higher-lying areas is used solely for the drainage of rainwater . In contrast to all other methods of pressure drainage, this is a gravity drainage , as it works without the use of external energy and pumps.
- in means of transport is used for individual drainage objects or for compact wet cells. See: vacuum toilet
- is occasionally also used to drain dirty water inside buildings, in particular to save water when flushing toilets.
Special drainage of wastewater
Wastewater cannot always flow freely downhill to the nearest public sewer system or sewage treatment plant. Pressure drainage methods have also been used in Germany since the late 1960s, and are described as special drainage methods in worksheet A 116 of the DWA .
Systems of this type often represent an economical alternative to the gravity sewer in sprawled residential and recreational areas with unfavorable terrain or soil conditions , as this often becomes uneconomical with decreasing population density, especially with regard to construction costs.
Overpressure systems with decentralized pumps are mostly used. With 50 or more connected properties, vacuum drainage systems can also be operated economically. Both are usually designed as separation systems, i.e. H. the domestic wastewater generated is disposed of separately from the rainwater.
Overpressure drainage
The wastewater from the connected buildings is fed into collecting shafts on the property and from there pumped into a pressure pipe network. The spur lines coming from the collecting shafts flow into the main line, which conveys the wastewater to the next sewage treatment plant, into a collecting pumping station or into another sewer network.
The sewage collection shaft is usually made of plastic ( polyethylene ) or concrete and is equipped with a submersible pump that transports incoming sewage into the collecting line. The power supply for the pump mostly comes from the connected building. If there is a combined system of pressure drainage and free-fall sewerage in a city or municipality, the residents of the pressure drainage system are often relieved of the additional electricity costs through somewhat lower wastewater contributions.
The pressure in the system required for transporting the wastewater is either applied by the pumps in the connection shafts alone or fed to a central collection pumping station. The pressure lines can be led to the sewage treatment plant in various network forms (branched network or ring network).
There are a number of advantages in favor of using cutting wheel pumps , which shred the solids contained therein:
- They homogenize the wastewater. This can have a positive effect on the overall efficiency of the system and, under certain circumstances, on the purification of the wastewater.
- The risk of clogging in the system is reduced.
- Smaller pressure line diameters are usually possible. Pressure lines from the nominal size DN 32 can be laid with significantly less effort and slightly less interference with the surface. Often these lines can be laid trenchless with special methods.
- There are hardly any blockages in branch and collecting lines, since impermissible contaminants are crushed directly in the connection shaft of the person causing them, block the pump or at least can be detected. With other drainage methods, the cause often cannot be determined.
Vacuum drainage
economics
Pressure drainage can be an economical alternative for municipal drainage compared to conventional gravity sewers for several reasons:
- Only a few inspection shafts are required in the collecting lines. This saves construction and operating costs and reduces the space required by the main lines.
- The course of suction and pressure lines is relatively independent of the terrain gradient.
- Obstacles (e.g. supply lines, other crossing canals, other underground structures) can be bypassed more easily and more cheaply than with the free fall canal.
- A significantly lower installation depth is required for suction and pressure lines than for the free fall sewer.
- Since the pressure drainage is a closed system, there is hardly any odor nuisance. These can possibly become a problem with free gradient drainage in warm summers.
- With negative pressure drainage ( vacuum drainage ), damage to the connection stations can have a detrimental effect on the rest of the system.
The energy costs for decentralized pumps are often viewed critically with overpressure drainage. In well-planned pressure pipe networks or when connecting a single house, the costs for a four-person household are only around 10 euros.
The "guidelines for the implementation of dynamic cost comparison calculations" of the state working group on water ( LAWA ) facilitate the system comparison. Investment costs, operating costs and service life are taken into account. The prerequisite for an objective comparison of variants is the same planning depth.
Web links
Legal information on pressure drainage, Juraforum.de
Footnotes
- ↑ Jens Friedemann: Introduction to urban drainage , Werdau, June 2003, Institute for Water Management Halbach
- ↑ Uwe Eichhorn: Comparison between gravity and pressure drainage, excerpt from the brochure "Wastewater costs 2000 for East German municipalities and associations", pages 78 to 86 (Annex), 2000, Halbach Institute for Water Management