Sewerage

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Sewer in Paris
Sewer in Paris
Shaft in Brighton
Ancient sewers (Athens)
Plan of the sewer system of Vienna , 1739

A sewer system is a system for collecting and discharging sewage , rainwater or meltwater through underground channels in the course of sewage disposal . Regional names for the sewer system are Dole , Siel or Schleusung.

In addition to the sewer network, the sewage system also includes collection, pumping, shut-off and mechanical cleaning systems. The collected wastewater is transported to wastewater treatment plants (mostly sewage treatment plants ) or discharged directly into bodies of water , referred to in this context as receiving waters .

Sewerage partly coincides with the term drainage system . According to DIN EN 752-1: 1995, this is "a system of pipes and additional structures for the discharge of wastewater and / or rainwater to a cesspool, sewer system or other disposal facility".

When the canalization of natural flowing waters is completely covered, one speaks of piping . Examples are the Darmbach in Darmstadt, the Salzbach in Wiesbaden with its tributaries, the Wuppertal Briller Bach and the Mirker Bach , in Austria the Grazbach in Graz and the Wienfluss in Vienna.

development

With the formation of contiguous settlements, hygienic problems arose from waste , sewage and flooding. The easy availability of drinking water was a major reason for the emergence of settlements on streams and rivers. The bodies of water could be used as a natural receiving water at the same time to discharge the waste water.

Before underground canal systems were created, sewage initially ran open in gutters along the streets and collected in small streams and other natural bodies of water .

In order to be able to divert flood and rainwater quickly, the first sewer systems developed in settlements, which are also known as flood sewer systems, since dirt and waste were washed away by the rainwater , while sewage on the individual plots was mostly seeped away .

The first drainage canals can be found around 3000 BC. In the Euphrates valley . From approx. 2600 to 1800 BC The Indus civilization spread across what is now Pakistan . She knew cobbled streets with gullies and house toilets that fed brick drainage channels. These are counted among the oldest sewer systems in the world. In Mohenjo-Daro , the brick-built house connections and canals that drained the sewage can still be seen today. In Roman times , alluvial sewers were used; Most of the time, however, they were open channels, and because of the high construction costs, sewer pipes were rare. The most famous Roman sewer system is the Cloaca Maxima in Rome . The remainder of an underground Roman sewer system in Cologne's old town is still accessible today.

In the early European Middle Ages, knowledge of the hygienic importance of an orderly sewage disposal was largely lost, which is why the growing population over the centuries led to major cholera epidemics . It was only in the modern era that an orderly sewage disposal system was installed in cities that had grown rapidly due to industrialization . In 1739 Vienna was the first city in Europe to be completely canalized. In the year of the Great Fire of 1842 , construction of the first modern sewer system on mainland Europe began in Hamburg . From 1856 onwards, after experiencing several cholera epidemics, London intended to build a sewer system. The project was finally decided in the year of the “ Great Stench ” (1858).

The sewer system of Berlin-Charlottenburg around 1900 together with a depiction of the sewage fields in Gatow .

Taking Berlin as an example , four phases of modern water management in metropolitan areas can be distinguished: 1856–1874, 1874–1900, 1900–1925, 1925–1940. Today's Berliner Wasserbetriebe were implemented in the first phase by an English private company. The municipal handover of the waterworks took place in 1874. After that, a comprehensive basic supply was built up by 1900. The sewage was trickled out on urban estates located outside the city at that time . The construction and expansion of an efficient sewer system, however, began later in the second phase. In Berlin at that time, long empirical investigations under the direction of Rudolf Virchow avoided serious technical errors in the design and construction of the sewer system and thus high bad investments, in contrast to Frankfurt, Düsseldorf, Essen and Münster, for example. The development of biological wastewater treatment and the activated sludge process followed in the years 1900–1940.

In rural areas, today's sewer system was usually created through the so-called mayor canals .

Today, many sewage networks are being rehabilitated to enable the cleaning of small amounts of sewage. The Leipzig mixed water network with a length of more than 2,700 kilometers has a so-called sewer network control. This system can be used to temporarily store large amounts of rainwater, such as those that occur during heavy rain, in the sewer. The water is then gradually diverted to Leipzig's largest sewage treatment plant in the Rosental . The system not only relieves the wastewater treatment plant and protects it from flooding, but also protects the environment because significantly less mixed water has to be discharged into surrounding waters such as Elstermühlgraben or the Parthe in heavy rain .

Dewatering process

Today, the sewerage system is mainly fed from municipal sewage from households and small businesses and a large part of the rainwater from roofs and sealed surfaces ( street drains ). Due to contamination by mineral oils , salts or other chemicals , industrial wastewater is mostly pre - treated in the company's own sewage or separator systems before it can be discharged into the public systems.

While wastewater in Germany and Austria was directed into cesspools and septic tanks until the 1960s (in rural areas in exceptional cases until today) , in recent decades these house systems have been combined in local sewers by the municipalities and sent to sewage treatment plants . The public sewer network consists of canals, shafts, special structures (rain overflow basins, sewage pumping stations, pumping stations, curved structures, outlets) and, depending on the local statutes, connection lines up to property boundaries or inspection shafts.

Types after drain

After the drain, a distinction is made between the following drainage systems:

Mixed system (mixed sewer system)

House, industrial and precipitation wastewater are discharged together.

Modified mixed sewer system

Wastewater and precipitation wastewater requiring treatment are discharged together. Precipitation wastewater that does not require treatment is seeped away on site or discharged directly or indirectly into a body of water.

Separation system (separation sewer system)

Wastewater is discharged in a canal, rainwater in a separate canal. Due to the generally low pollutant load of rainwater, it is usually discharged directly or indirectly (e.g. via rainwater retention basins) into bodies of water and not treated in sewage treatment plants.

Extended separate sewerage

Wastewater and rainwater that needs treatment are drained off in separate channels. Precipitation wastewater that does not require treatment is seeped away on site or discharged directly or indirectly into a body of water.

Special procedure

In the case of remote buildings or settlements, depending on the volume and quality of the wastewater, pressure or vacuum drainage methods and storage in drain-free collection pits with disposal by vehicles can be used to dispose of the wastewater. Supply channels are also required for local wastewater treatment using small wastewater treatment plants ( trickling filters , activated sludge processes , plant-based wastewater treatment plants and sewage fields (sewage irrigation)). In some cases there are also additional canal systems for drainage or external water that lead directly into a receiving water.

In Germany, the mixed sewer system still predominates today, with which around 60% of the settlement areas of all residents are drained. When building new systems, a separate sewer system is required according to the Water Resources Act. The drainage concept has also changed in recent years. From the discharge-oriented point of view and in the sense of an economic and ecological point of view, decentralized rainwater infiltration on site is becoming increasingly important.

Types by size

A distinction is made according to size:

House sewerage

Nowadays, pipes with a nominal width of DN 100 (pipe diameter 10 cm) to DN 200 (20 cm) are mostly used on private properties . The house sewer system includes sinks, toilets, roof vents and internal gullies (the drainage objects). The house sewer system is disposed of in the public sewer system or flows into wastewater treatment plants or drain-free collecting pits in the immediate vicinity of the object to be drained. The drainage objects in a house are connected via odor traps ( siphons ) and drained to the downpipes. The downpipes open into the basic sewer, which directs the wastewater to the house connection shaft. A sewage lifting system for lower floors may be required. In order to avoid damage caused by backflow from the sewer network and the resulting flooding, all drainage objects should be located above the backflow level (mostly the top edge of the street, since when the local sewer system is overloaded, the sewage escapes through the manholes and therefore the water level in the local sewer can only rise up to there) . Backflow protection must be provided for drainage objects below the backflow level, but are not completely reliable if they do not comply with the relevant standards. Since the drainage system in the building has to follow the separation system , the downpipe of the gutters must not be closed to the underground pipe. This is best done in the revision shaft. The downpipes must be ventilated via the roof to prevent odor traps from being sucked empty and to enable odors to be discharged from the sewer system. For this reason, no odor traps should be provided in basic ducts either.

Cleaning openings should be arranged in the house connection shaft and in the drainage network. Plastic , gray cast iron or stoneware are mostly used as the material for house sewer systems. The choice of material depends on the aggressiveness of the wastewater (for small businesses), the pipe diameter, the processing and the costs.

Local sewerage

These include the connection channels that flow into street channels that are brought together to form secondary and main collectors. Nowadays, pipes with the designation DN 250 (pipe diameter 25 cm) to DN 800 (80 cm) are mostly used. The main collectors direct the wastewater to a sewage treatment plant. In addition to the pipeline network, there are storage basins as well as rain overflows and rain basins that flow directly into receiving waters. If longer distances - as in rural areas - or differences in altitude have to be overcome, pumping stations are also used. In the past, gray cast iron or stoneware was used as the material. Since the end of the 20th century, plastic has been used increasingly in the course of technical developments.

channels

Sewers usually have a gradient of 0.5 to 2% and a nominal width between 200 mm (or DN 250 according to the newer technical rules) and sometimes several meters. The channels are usually designed as so-called gravity lines so that the water level in the pipe is below the top of the pipe. The channels are only completely filled with sewage in exceptional cases; for example in the event of heavy rain events in mixed or rainwater sewers. In special cases, e.g. B. If there is a slight gradient in the catchment area or transport lines, negative pressure systems or pressure lines are used. If the pipe gradient is too small or if there are slopes to be overcome, additional pump systems must be provided. Inspection shafts are located between longer pipe sections . The pipes have large cross-sections compared to drinking water pipes. Main sewage collectors in metropolitan areas can be made accessible and in some cases even navigable by boats; so the Geest-Stammsiel at the Hamburg Landungsbrücken . In some European countries and cities (e.g. Paris ) the accessible canals were also used to lay supply lines (water, gas, electricity), which is not common in Germany. For remote settlements, such as remote homesteads or weekend house settlements, pressure or vacuum drainage or, in order to avoid long canals, decentralized small sewage treatment plants are used in exceptional cases. In the past, channels were often built up from bricks or made of clay or stoneware pipes. Depending on the medium and the load on the pipes, ducts are now made from a wide variety of materials such as fiber concrete , cast iron , steel , stoneware, plastic or concrete .

Mixing and separating system

In principle, there are two ways of disposing of the dirty water and the rainwater. Either in a common line ( mixed system or mixed process) or in separate lines (separate system or separate process). Both methods have their advantages and disadvantages.

costs

The mixed method usually causes lower construction costs for the line construction than the separation method, since only one channel is necessary. Sewage treatment plants and pumping stations, however, have to be dimensioned for large amounts of water and are therefore structurally and operationally more expensive. The separation process has the advantage of smaller sewage treatment plants and pumping stations with correspondingly lower construction and operating costs. In terms of price, both systems are therefore roughly the same.

change

In the past, the mixing system was often given preference over the separation system, not only because of the lower investment costs, since relatively little wastewater was assumed and heavy rain was seen as a welcome flushing of the pipe network. The infrequent overflow of the heavily diluted wastewater via a rain overflow structure into the receiving water could therefore be tolerated, but the dirt of the streets was kept away from the receiving water at the beginning of rain and during smaller rains.

The increasing population and lengthening of the sewer lines have led and continue to lead to an ever increasing waste water base load and overload cases are becoming more frequent. This creates backwater of the sewage in the basement and flooding of streets, which is particularly unpleasant because of the faeces carried along. Further relief structures and backflow stops are being built. Due to the overload cases, the faeces reach the receiving water uncleared, which makes the biochemical pollution too great or new and larger sewer systems and structures are required.

This is why the separation system has been increasingly used since the 1970s. In the meantime, attempts are often made in urban planning to merely discharge the wastewater in a sewer system and to infiltrate rainwater on site, so a corresponding design is required. This can also reduce costs.

Special structures

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A special structure is a structure of the sewage system that is not a shaft or a sewer. The types of construction of special structures are described in worksheet ATV-DVWK-A 157 "Sewer structures".

Rain relief structures

A rain relief structure is a facility in a mixed or modified mixed system or a sewage treatment plant that relieves the system hydraulically.

The following structures are considered rain relief structures:

The sewer system cannot be dimensioned to discharge all of the waste and rainwater that accumulates. Relief structures must therefore be built in the combined sewer network.

From certain rain intensities and the associated wastewater quantities, parts of the wastewater are diverted into a receiving water via rain overflows for relief.

Rain basin

The rain basins are arranged where the conditions for flood relief are not reached or the flood relief starts too often and pollutes the receiving water with dirty water.

The rain basins can have three functions.

  1. Saving the excess wastewater.
  2. Rough clarification of the overflowing mixed water.
  3. Catching the first bump of dirt, which mainly results from washing away the sewer deposits.

The effect of the rain basin depends on the ratio of the basin contents to the size of the catchment area.

There are the following reasons for building a rain basin.

  • Overloaded networks can often be purposefully rehabilitated by installing rain basins without enlarging the existing sewers. Pumps must also be switched on depending on the gradient.
  • When connecting new construction areas to an existing, almost fully utilized sewer system, there is often the option of discharging the wastewater and part of the rainwater, but not the peaks in runoff, into the existing sewers. The extension of the existing sewer system can be avoided by installing a rainwater retention basin.

Depending on the mode of action, the following types of pools are distinguished under the collective term "rain basin":

  • Rainwater retention basin (RRB)
  • Rain overflow basin (RÜB)

Rainwater retention basin (RRB)

In the event of heavy rainfall, rain retention basins store part of the incoming mixed water volume and release it back into the sewer system in a delayed and restricted manner. They prevent overloading in the sewer network, where relief is impossible or not desired. Such basins do not have to be close to receiving waters. They usually only have one drain into the network and an emergency overflow.

Rain overflow basin (RÜB)

Rain overflow basins represent a combination of rain overflow and rain retention basin. The two components, basin and overflow, can be implemented separately or combined in one structure. These basins have a basin drain and one or more overflows. The rain sewage is roughly treated and fed to the receiving water. The tank contents with the retained, deposited substances are fed to the sewage treatment plant. This breaks the peaks of the runoff and reduces the amount of water to be discharged.

The rain overflow basin acts as a retention basin until the overflow starts. Only when it is filled, with overflow operation, does it become a clarifier through which the water flows. Rain overflow basins can be operated in the main or shunt.

So that the rain basins can be optimally managed, the rain overflow basins are built in a shunt today. Basins operated in the main circuit are located in the sewer leading to the sewage treatment plant. This important arrangement is only possible with a sufficient slope, as the basin is emptied continuously and only with a natural slope towards the sewage treatment plant. The basin is only emptied after the rain has ended using a pump. If the gradient is sufficient, the pool can also be emptied using a controlled slide after the rain has ended.

They forward at least the critical mixed water runoff Qkrit to the sewage treatment plant. This results in a mixing ratio

mRÜ = (Qdr - Qt24) / Qt24> 7, the mixing ratio of mRÜ = 7 for the RÜ is to be used.

If the mean COD concentration in the dry weather runoff ct is above 600 mg / l, the mixing ratio m must be increased in order to achieve greater dilutions:

mRÜ ≥ (ct - 180) / 60

The overflows should, if possible, be designed with a raised weir. Diameter of a throttle pipe du> 0.2 m. An RÜ with a floor opening (spring overflow) makes sense when the drain is closing.

An RÜB should have a minimum storage volume. Vs min = 3.60 + 3.84qr in m³ / ha

Continuous basins (DB) should have Vs> 100 m³,
Catch basins (FB) should have Vs> 50 m³.

Catch basin (FB) in the shunt

A catch basin is used to catch the first surge of water when it rains and to relieve the canal. Normally the canal flows through them. In addition, they are fed via separating structures. After the pool is filled, the pool overflow comes into action. There is no loss of gradient. In dry weather and small rain with QR <Qab no inflow to the basin. Emptying by pump with constant additional feeding of the sewage treatment plant.

In the main end, the sewage plant inflow goes through the basin. Simple arrangement, no separating structure, possible loss of gradient, draining without a pump, fluctuating drain without a control device.

Flow basin (DB) in the bypass

Continuous basins also have an overflow for clarified water (clarification overflow), which starts in front of the basin overflow and directs the mechanically clarified mixed water in the basin to the receiving water.

Storage ducts (SK)

Storage ducts with relief at the top are usually dimensioned like catch basins, provided that the conditions for catch basins can be met. Otherwise they are to be treated like storage ducts with relief at the bottom. They are also useful for storage volumes smaller than 50 cubic meters.

Storage ducts with relief at the bottom receive a volume surcharge in the simplified division process because of the poorer settling effect. The specific storage volume Vs is to be determined as for rain overflow basins.

VSKU = 1.5 • Vs • Au in m³ With Vs in m³ / ha = specific storage volume Au in ha = impermeable area of ​​the associated sub-catchment area

In verification procedures, the special features for storage ducts with relief at the bottom must be observed. The emptying time of storage ducts should be less than 15 hours. The minimum mixing ratio is to be determined as for rain overflow basins.

Organization and costs

Opened sewer manhole

Germany

The construction and maintenance of the public sewer system and the public wastewater treatment plants ( sewage treatment plants ) are the responsibility of the “wastewater disposal person”, usually the respective municipality. This can transfer the obligation to dispose of the wastewater to a third party, for example a wastewater association , or, under certain conditions, to the property owner who produces the wastewater, for example by building a small wastewater treatment plant.

For new connections to a public sewer system, a connection fee may have to be paid depending on the sewage statute. When connected to a central wastewater network, the usage fees are usually billed for the wastewater according to the drinking water consumption (probability scale) and the rainwater according to the connected sealed surface. In the case of a decentralized connection ( small sewage treatment plant ), the amount of faecal sludge removed is billed.

Austria

The construction, maintenance and operation of wastewater disposal systems is carried out by individuals, companies and companies, water cooperatives , municipalities and water associations .

The settlement of the sewerage costs is a municipal matter in Austria . There are basically three billing models for the current sewerage fees:

  • according to the area of ​​the connected building floors (more in rural areas)
  • according to the water consumption from the drinking water pipe (( water distribution system ), this distribution key is increasingly used in urban areas).
  • according to the number of connected toilet bowls combined with water consumption (as in Graz). If more than the included base water amount is consumed, the difference is offset using the second method.

In addition, connection fees must be paid for a new connection.

Switzerland

The Federal Office for the Environment (FOEN) is responsible for overseeing the enforcement of laws in Switzerland.

Local sewer networks

Cologne

The wastewater in Cologne is diverted, cleaned and fed into the Rhine via a sewer network of around 2,400 km to the five Cologne sewage treatment plants in Stammheim , Langel , Weiden , Rodenkirchen and Wahn . The total amount of wastewater generated by residents and businesses is equivalent to 1.82 million residents. Connected to the sewage treatment plants of the Stadtentwässerungsbetriebe Köln (StEB).

The sewer network is 2,385 km long, 591 km of which are accessible and 1,793 km are not accessible. There are 58,129 sewer shafts , 82 rain retention basins and canals, 674 flood valves , 190 operating valves . Three quarters of the wastewater volume is channeled through two large collectors in Niehl through two culverts under the Rhine to the large sewage treatment plant in Stammheim.

Paris

The construction of the Paris sewer system after 1852, especially by Eugène Belgrand under GE Baron Haussmann, was a milestone in the history of the city. A multiple water network was created under the earth's surface with two systems for fresh water (drinking water and non-drinking water (eau brute)) and one system for waste water. The merging of wastewater disposal was decisive for the connection of numerous Parisian households to the water network: Until then, the wastewater from private households had to be collected by them in containers and picked up by private companies. With the expansion of the networks, private households were given the opportunity to be connected to the public sewage system. Numerous reservoirs of different sizes were built underground in the middle of the city to regulate the water level. A hygienic problem also arose with the numerous flooding of the inner-city cemeteries, whereupon extensive reburies in underground quarries were carried out in the 18th century ( catacombs of Paris ).

Leak test

With the tightness test according to DIN EN 1610 , newly constructed or renovated sewers can be tested for tightness. For this purpose, all openings in the duct section to be tested are closed and pressed off with air or water . The recurring leak test of old sewers is carried out with lower test pressures.

Risk of explosion

There is a risk of explosion in sewer networks from biogas , the formation of which is promoted by the absence of atmospheric oxygen. In areas where coal was mined, leaks can cause mine gas to enter the sewer system.

See also

The chandelier hall of the Cologne sewerage system

literature

  • Christian Berger, Johannes Lohaus: State of the sewer system - result of the DWA survey 2004 . In: KA, Korrespondenz Abwasser, Abfall 52 (5), pp. 528-539 (2005), GFA, Society for the Promotion of Abwassertechnik, Hennef, ISSN  1616-430X .
  • Alexandru Braha, Ghiocel Groza: Modern wastewater technology: survey, model structure, scale up, planning . Wiley-VCH, Weinheim 2006, ISBN 978-3-527-31270-2 .
  • Willi Gujer: Urban water management . 3rd edition, Springer, Berlin 2007 ISBN 978-3-540-34329-5 .
  • Wilhelm Hosang, Wolfgang Bischof: Sewage technology . 11th edition, Teubner, Stuttgart 1998, ISBN 3-519-15247-9 .
  • Martin Illi; Stadtentwässerung Zürich (Ed.): From Schissgruob to modern urban drainage . NZZ Neue Zürcher Zeitung, Zurich 1987, ISBN 3-8582-3173-8 .
  • Axel Stefek: Weimar's early canals as reflected in urban development. In: water under the city. Streams, canals, sewage treatment plants. Urban hygiene in Weimar from the Middle Ages to the 20th century. Edited by Axel Stefek for the Weimar sewage company. Weimar 2012. pp. 15–74.
  • Klaus Mudrack: Biology of wastewater treatment . 5th edition, Spektrum, Heidelberg 2009, ISBN 978-3-8274-2576-8 .
  • Helmut Resch, Regine Schatz: Understanding wastewater technology: A small 1 × 1 in wastewater technology for beginners and interested laypeople . Hirthammer, Oberhaching 2010, ISBN 978-3-88721-204-9 .

Web links

Wiktionary: sewerage  - explanations of meanings, word origins, synonyms, translations
Commons : Sewers  - Images and Media Files

Footnotes

  1. ↑ Eau potable / Eau non potable. Retrieved October 29, 2019 (French).
  2. ↑ W. Kuipers et al .: Autonomous flame ionization detector for explosion protection in sewer networks . In: Technical Security . tape 7 , no. 11/12 , p. 19-24 .