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Wastewater is a generic term for water from various sources that is conveyed through structural systems:

  • Rain water - runoff from paved areas rainwater ; In some contexts, rainwater is not counted as wastewater
  • Wastewater - water that has been contaminated through use ("changed in its properties or its composition"), which is further differentiated:
    • Gray water - according to EN 12056-1, faecal-free, slightly contaminated wastewater, such as occurs when showering, bathing or washing hands, but also comes from the washing machine and can be treated to process water or process water. This also includes rainwater running off the roof or balcony .
    • Black water - according to ISO 6107-7: 1997 domestic sewage with urine and / or faecal solids; Black water can be further divided into:
  • Extraneous water that enters the sewage system due to structural damage

Wastewater is collected and transported in the sewer system in the course of wastewater disposal , usually treated in sewage treatment plants in Central Europe and then discharged into waters that serve as receiving waters or into the groundwater through seepage , trickling or rain . The thermal energy contained in the waste water can be used with systems for waste water heat recovery for hot water and heating purposes.

The municipal water management is concerned with the discharge and treatment of waste water.


Rainy weather runoff

Rainwater consists primarily of rainwater and meltwater . Since rain releases dust , soot , pollen and gases from the atmosphere and carries away pollutants present on roofs, paved and agricultural areas , precipitation runoff can in some cases require treatment.

One distinguishes

  • rainwater in need of treatment that is discharged into rainwater clarifiers or sewage treatment plants, and
  • Rainwater that does not require treatment ( pure wastewater ) that can be discharged into nearby bodies of water or seeped away on site .

Examples of pure wastewater are:

  • Overflow water from springs, reservoirs, wells
  • Return water from cooling and air conditioning systems, heat pumps
  • Drainage and seepage water

Dry weather runoff

Wastewater is domestic wastewater from toilets (faecal or black water ), sanitary facilities, kitchens and washing machines (washing or gray water ) as well as wastewater from companies that discharge into the public sewer system ( commercial or industrial wastewater; in short: industrial wastewater ). Industrial wastewater can be particularly polluted, which is why it is often pretreated in gasoline, oil or grease separators and similar systems before it is discharged into the public sewer system (indirect discharge, mixing) or into a body of water (direct discharge). Some wastewater contains organic substances (e.g. brewery wastewater) and / or inorganic substances (e.g. from the metal and basic industries). Heated water from cooling systems (cooling water) also counts as wastewater. Wastewater that arises from the various cleaning and treatment technologies in water treatment plants is also counted as industrial wastewater.

Extraneous water is the unpolluted water that runs off together with the dirty water in dry weather and is actually not supposed to get into the sewer system ( groundwater , drainage water ).

The separation of yellow water and brown water in special toilets facilitates wastewater treatment and further use. Brown water does not contain urine and can be used as fertilizer after dehydration .

Mixing and separating system

In the mixed system , dirt and rain water flow off together.

In the separation system, on the other hand, the only slightly polluted rainwater is discharged and treated separately from the dirty water in a second channel. A danger in the separation system comes from incorrect connections, which u. a. domestic wastewater is discharged into the rainwater sewer and thus gets into the environment almost uncleared. Here one speaks of extraneous water. The reverse case, in which rainwater is led into the sewage channel, is often also undesirable because the dilution of the sewage can impair its cleaning.

Legal Definitions

The term wastewater is defined in the Federal Republic of Germany in Section 54 (1) of the Water Management Act (WHG) of July 31, 2009 ( Federal Law Gazette I p. 2585 ) and the Swiss waste water disposal standard SN 592,000. According to this, wastewater is the water that has changed its properties through domestic, commercial, agricultural or other use and the water that runs off together with it in dry weather (dirty water) as well as the runoff water collected from precipitation from the area of ​​built-up or paved areas (precipitation water). The liquids escaping and collected from facilities for the treatment, storage and disposal of waste are also considered to be waste water. The definition previously existing in the Waste Water Tax Act was adopted word for word.

In Austria , issues related to wastewater law are dealt with in the Water Law Act , the emission ordinances and the sewer connection laws of the federal states as well as the associated ordinances at the municipal level.

Waste water volume

Private water consumption and thus the amount of wastewater has decreased in Germany in recent years. According to the German Association for Water Management, Sewage and Waste ( DWA ), the average amount of wastewater produced per person per day fell from 147 liters in 1990 to 127 liters in 2004.

Water consumption will continue to decline in the foreseeable future, because rising energy costs, constant maintenance and repair costs with decreasing water consumption will result in fee increases for the individual household. Furthermore, due to the demographic development in Germany, the sewage (indirect) discharges will decrease. For areas such as Saxony , Saxony-Anhalt and Thuringia, official demographic reports show that the population will be reduced by up to 20% over the next 15 years. In addition to a positive aspect of the protection of the drinking water resource, the declining water consumption also has a negative impact on the functioning of the drainage facilities, the maintenance and wastewater treatment that becomes necessary and ultimately on future cost developments.

One reason for this can be seen in the fact that wastewater systems in Germany have been dimensioned and constructed based on key parameters such as water consumption of 130 to 150 liters per day and person. These values ​​are sometimes undercut dramatically: in Saxony, the average consumption in 2005 was only 88 liters per day and person. The sewage system is also usually designed for a constant number of users. A significant shortfall of the key parameters leads u. a. to increased deposits in the sewer and an extension of the flow time to the wastewater treatment plant with many negative consequences, such as B. the sulphide formation in sewage systems. The effects are changed wastewater parameters, increased effort for wastewater treatment, odor nuisance, bio-corrosion and finally an increased need for remediation in shorter time intervals. To remedy this, clean drinking water is already being used to flush the sewer pipes, because the amount of wastewater that arises is too small to flush the sewer system.

The clothing industry is responsible for 20 percent of wastewater worldwide .


Wastewater consists of around 99 percent water and 1 percent pollutants. Dirty substances in wastewater are in dissolved and undissolved form as well as organic compounds ( fats , proteins , carbohydrates ). A distinction is made between the following wastewater constituents:

such as uric acid , glucose . They are biodegradable and lead to odor nuisance during anaerobic degradation processes. The oxygen consumption triggered by these substances reduces the oxygen content in the surrounding water and can lead to fish deaths ( eutrophication ).
such as nitrogen and phosphorus compounds , which lead to the eutrophication of stagnant water in particular and are also responsible for increased algae growth in the seas.
such as poisons , heavy metals , synthetic organic substances (such as microplastics , drugs , detergents etc.), bacteria , fungi or viruses that can lead to diseases.
such as salts , fats , oils , clays , sand

Depending on the composition of the waste water are different methods for the waste water treatment required.

Wastewater treatment

Wastewater treatment plant in Wilhelmshaven
Wastewater treatment plant in Schiffdorf

The aim of wastewater treatment is to remove the constituents of the wastewater from the water and to restore the natural water quality. This counteracts excessive nutrient input into water. In the Federal Republic of Germany, according to § 57 WHG, waste water must be treated according to the state of the art before it is discharged into a body of water (direct discharge) . Minimum requirements for certain industrial sectors are specified for Germany in the wastewater ordinance. The discharge into public sewage systems (indirect discharge) is regulated by § 58 WHG.

The wastewater treatment takes place in sewage treatment plants, possibly after pretreatment of industrial or commercial wastewater, e.g. B. in a separator . One differentiates

  • mechanical / physical cleaning processes
  • biological cleaning processes
  • chemical cleaning processes

Water that potentially contains mineral oil because it contains e.g. B. was used to wash cars or may have come into contact with substances hazardous to water (e.g. filling areas of a petrol station), must be pretreated in a separator system according to EN 858 / DIN 1999 before being discharged into the sewer .

In addition to treatment in technical wastewater treatment plants, wastewater can under certain circumstances also be treated in wastewater ponds and plant treatment plants.

The treatment of wastewater outside central wastewater treatment plants takes place in small wastewater treatment plants . A distinction is made between outdated systems without wastewater aeration (DIN 4261 Part 1) and the fully biological small sewage treatment plants with ventilated purification levels (DIN 4261 Part 2) that are required today.

On the way from the place where the wastewater accumulates to the wastewater treatment plant, processes take place that change the wastewater. It can lead to the formation of odorous and hazardous substances, such as B. the toxic hydrogen sulfide (H 2 S), come what

  • has negative effects on the wastewater treatment process,
  • is the main cause of odor nuisance (H 2 S smells like rotten eggs),
  • can be dangerous for people (H 2 S is a nerve gas that is fatal even in low concentrations; death in a few moments at 1000 ppm),
  • Can destroy sewage structures and facilities and
  • if discharged into a body of water without treatment , it can cause water pollution and fish death .

Appropriate measures, such as B. through an inter-stage wastewater treatment in drainage systems , these processes can contain or make controllable.

Wastewater that occurs in water treatment plants is more and more often treated again in these plants (circulation). This increases the net yield of pure water and reduces the amount of residual waste water to be discharged. The treatment of rinsing wastewater in treatment plants for drinking and bathing water is given as an example . In areas with a lack of water, the partial recirculation and reuse of regeneration waste water is also economical. However, only the flow and residual wash water quantities that do not have a higher salt content than the raw water are suitable for this.

Decentralized wastewater treatment and disposal

Sewage pumping shaft

In the Federal Republic of Germany, households and equipment that are not connected to the central sewage disposal, the waste water either in a sump to catch and let then transported away by the sanitation agent or its own wastewater treatment plant to be treated to make it then discharged directly into a water body or to seep or trickle away. In this case, the responsible water authority transfers the obligation to dispose of wastewater to the property owner, usually in connection with the granting of a permit to use the water . The state of the art is considered to be complied with if the requirements specified in the annexes of the waste water ordinance for the respective area of ​​origin of the waste water are complied with. For small wastewater treatment plants for the treatment of domestic wastewater, the requirements of the wastewater ordinance are deemed to have been met if they have a general building inspection approval.

Type-approved small wastewater treatment plants have been tested on an official test field and can reliably guarantee the legal requirements for the wastewater treatment plant flow, usually a chemical oxygen demand (COD) below 140 and a biochemical oxygen demand within 5 days (BOD 5 ) below 40 mg / l. Have proven such. B. Systems based on the SBR ( Sequencing Batch Reactor ) or fixed bed process , trickling filters , membrane activated reactors (MBR) and near-natural cleaning processes such as plant-based sewage treatment systems or sewage ponds.

The use of small sewage treatment plants is usually neither ecologically nor economically sensible. It is true that the disposal costs of the sewage sludge produced in these plants are considerably lower due to the smaller quantities. The investment costs, however, correspond to a multiple of the costs of simple septic tanks. There are also costs for energy and maintenance. From the point of view of water protection too, small wastewater treatment plants tend to be a problem because the cleaning requirements placed on them are much more moderate. For example, there are no limit values ​​for phosphorus and the various nitrogen compounds.

See also


  • Thomas Kluge , Jens Libbe (ed.): Transformation of network- bound infrastructure. Strategies for municipalities using the example of water . (= Difu contributions to urban research, Volume 45). Difu, German Institute for Urban Studies, Berlin 2006, ISBN 3-88118-411-2 .
  • Jens Libbe, Ulrich Scheele: Spatial aspects of quality and supply standards in the German water industry . In: Federal Office for Building and Regional Planning (ed.): Infrastructure and services of general interest in the area. Information on spatial development. 1/2 2008, ISSN  0303-2493 , pp. 101-112.
  • Theo Mann: The development of wastewater technology and water pollution control. In: Chemistry in Our Time . 1991, 25, pp. 87-95, doi : 10.1002 / ciuz.19910250205 .
  • Dieter Weismann, Theodor Gutzeit: Municipal sewage pumping stations . 2nd Edition. Vulkan, Essen, ISBN 3-8027-2843-2 .
  • Dieter Weismann, Manfred Lohse (Hrsg.): Sulfide Praxishandbuch der Abwassertechnik; Prevent odor, danger and corrosion and control costs! Vulkan, Essen 2007, ISBN 978-3-8027-2845-7 .
  • Diana Hummel, Alexandra Lux: It doesn't work out: fewer people = lower water consumption. Population decline challenges utility system planners. In: Research Frankfurt . 24 (1) (2006), ISSN  0175-0992 , pp. 60-63.
  • Hans-Jürgen Leist: Water supply in Germany - criticism and possible solutions . (= University publications on sustainability, Volume 35). oekom, Munich 2007, ISBN 978-3-86581-078-6 . (at the same time dissertation at the University of Hanover 2007 under the title: Use of water resources and drinking water supply from the perspective of integrated environmental protection )
  • Becker Büttner Held (Hrsg.): DWA topic volume wastewater disposal and energy law. 2nd Edition. DWA, 2010, ISBN 978-3-941897-40-3 .

Web links / sources

Wiktionary: wastewater  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Fashion is an environmental and social emergency, but can also drive progress towards the Sustainable Development Goals. In: . 2018, accessed on November 6, 2019 .
  2. UN World Water Report, 2017
  3. Wastewater Ordinance, Appendix 1, Section C, Paragraph 4.