Wastewater Indirect discharger Limit values

There are limit values for indirect dischargers in the wastewater that must always be complied with when discharging wastewater in accordance with the individually required indirect discharger permit. In principle, an official permit is required for any non-domestic discharge of wastewater, i.e. any water used commercially or industrially (except: uncontaminated rainwater and sanitary wastewater), a so-called indirect discharger permit, in which the limit values to be complied with in the specific case are specified, under certain circumstances also for process water treatment (e.g. from reverse osmosis system) also below the exemption limit of 10 m³/week. An indirect discharger application is required for this indirect discharger permit.

The indirect discharger application must contain detailed information on the location, production process and wastewater treatment, in particular on the following points: Where does the water for production come from, what is actually done with it and how is the wastewater treated?

The first step is to identify which annex of the Wastewater Ordinance (AbwV) applies to the respective company. As a rule, these are at least two annexes from the AbwV. Depending on the respective quantities and the wastewater treatment, these annexes then apply either at different points or together, but then possibly with a mixing rule, which must be considered in each individual case. The individual annexes to the AbwV are subdivided into parts A to E. However, Part C does not apply to the indirect discharger. However, this does not mean that this part remains unregulated; instead, the statutes of the municipal wastewater treatment plant, which are often based on the DWA model statutes, apply to indirect dischargers.

Essentially, the limit values from the Wastewater Ordinance for indirect dischargers are summarized and simplified as follows (deviations possible – depending on the annex and specific individual case, the specific decision in the individual case is decisive):

  • AOX usually 1 mg/L
  • Arsenic usually 0.1 mg/L
  • Barium usually 2 mg/L
  • Lead usually 0.5 mg/L
  • Cadmium usually 0.1 mg/L
  • Chlorine, free, usually 0.5 mg/L
  • Chromium, total usually 0.5 mg/L
  • Chromium VI usually 0.1 mg/L
  • Cyanide, easily releasable, usually 0.2 mg/L
  • Cobalt usually 1 mg/L
  • Copper usually 0.5 mg/L
  • Nickel usually 0.5 mg/L
  • Mercury usually 0.05 mg/L
  • Selenium usually 1 mg/L
  • Silver usually 0.1 mg/L
  • Sulphide, easily releasable, usually 1 mg/L
  • Tin usually 2 mg/L
  • Zinc usually 2 mg/L

In addition, the parameters of the local drainage statutes, i.e. the municipal monitoring values, also apply to indirect dischargers. However, these often apply at a different sampling point. Of particular note are the monitoring values for

  • Sulphate generally 600 mg/L or 3,000 mg/L (virtually unattainable in some sectors)
  • Fluoride usually 50 mg/L (or 20 mg/L)
  • Phosphorus usually 50 mg/L
  • pH generally 6.5 – 9.5
  • Temperature: 35°C
  • Colorants: clear

Note: Various tightening of these limit values are currently (as of 05/2023) under discussion, in particular a general tightening by 10%, silver is to be reduced to 0.50 mg/L, exceptions for AOX are to be reduced, PFOS is to be generally introduced at 10 µg/L (possibly However, other PFT/PFOS or PFAS parameters (possibly also as sum parameters PFT6/PFT20), in particular H4-PFOS or 6:2 fluorotelomer sulfonic acid (6:2-FTS), chromium VI should require pretreatment, mercury should be tightened to 0.00050 mg/L and cadmium to 0.0050 mg/L. It is not foreseeable whether and when these will be implemented.

If the limit values are violated or exceeded during indirect discharge, i.e. after chemical-physical wastewater treatment and possibly after a selective exchanger system at the respective monitoring point, i.e. if the wastewater contains more than the permitted quantity, various aspects must be taken into account, in particular with regard to administrative offenses and also environmental criminal law. Depending on the constellation, the 4 out of 5 rule initially applies, i.e. in an official measurement the limit value (or more correctly: monitoring value) may be exceeded by double, that means e.g. 1.0 mg/L copper. If a value is exceeded by more than double, there is another legal way out in some constellations. Please also see our separate article for these cases.

These aspects of operating an industrial chemical-physical wastewater treatment plant are also discussed in detail in our training courses.

Do you have further questions about wastewater indirect discharger limit values, such as an application for indirect discharge, problems with chemical-physical wastewater treatment or do you need support in communicating with authorities? Please do not hesitate to contact us.