Technical Information from A to Z

Here you have direct access to our A – Z of technical information for waste water chemistry. There are technical explanations and supplementary information for each of the keywords. Ingo Rürup will be happy to advise you and provide more specific information should you have any questions.


Nitrification is the bacterial oxidation of ammonia (NH) to nitrate (NO). It consists of two coupled sub-processes: In the first process, ammonia is oxidised to nitrite and oxidised to nitrate in the second sub-process. Both sub-processes provide the organisms involved with sufficient energy for growth and other life processes. In the nitrogen cycle of ecosystems, nitrification plays an important role because it converts the ammonia released by decomposer bacteria from dead biomass back into nitrate. This produces nitrogenous mineral nutrients for plants.


Denitrification is the conversion of the nitrogen bound in nitrate (NO) into molecular nitrogen (N) and nitrogen oxides through the activity of certain heterotrophic and several autotrophic bacteria, which are therefore referred to as denitrifying bacteria. This process generates energy for bacteria. In the absence of molecular oxygen (O) (anoxic conditions), different oxidizable substances (electron donors), such as organic matter, hydrogen sulphide (HS) and molecular hydrogen (H), use nitrate as the oxidant (oxidizing agent) for oxidization. The process is an alternative form of energy metabolism, namely an oxidative energy metabolism.

The nitrogen bound in nitrate is converted back into molecular nitrogen (N) through the denitrification process. It is transferred in a largely inert form and cannot be used as a nutrient (nitrogen source) by most living things. This means it is no longer available as a fertilizer in water and soil and no longer environmentally relevant. The resulting molecular nitrogen (N) largely escapes into the atmosphere, where it is already the main component. Denitrification is the only metabolic pathway for bound nitrogen to pass back into the molecular form and is, therefore, an integral part of the nitrogen cycle.

Quarterly contract price

In north-west Europe, contract agreements are almost always based on methanol’s quarterly contract price. This is determined once per quarter, usually around one to two weeks before the beginning of the quarter, between a major European producer and a major European consumer. As a consequence, all market participants, with a total volume of approximately 8 – 10 million tonnes, accept this quarterly contract price. Hence, the quarterly contract price is always a compromise between producers and consumers and reflects the current balance between supply and demand.

The quarterly contract price is published in such publications as PLATTS European Marketscan, ICIS Pricing and is also available on our website.

Waste Water Ordinance

The Waste Water Ordinance specifies the minimum requirements to be stipulated when granting a permit to discharge waste water into water bodies. Provisions for certain areas have been introduced for numerous plants. The ordinance also specifies analysis and measurement procedures. In 1997, the Waste Water Ordinance replaced the Waste Water Origins Ordinance of 3 July 1987 (Federal Law Gazette l.p. 1578) and the General Administrative Framework Regulation on Waste Water.

The Annexes to the General Administrative Framework Regulation on Waste Water were converted into Annexes to the Waste Water Ordinance. The background to this is that an administrative regulation only binds the administration and not the citizens and therefore EU directives can only be implemented by introducing a law or an ordinance.

  • See also: Appendix 1
  • See also: Appendix 51
Appendix 1

 Annex to the Waste Water Ordinance for Domestic and Municipal Waste Water (source of original text: Federal Law Gazette I 2004, 1118 – 1119)

A) Scope of application

This appendix shall apply to waste originating primarily from households or similar facilities such as communal accommodation, hotels, restaurants, campsites, hospitals or office buildings (domestic waste water) or from facilities serving some purpose other than the ones stated, provided it is equivalent to domestic waste water which is collected in the sewage system and originates primarily from the establishments and facilities specified in number 1 and from plants serving commercial or agricultural purposes, provided that the noxiousness of this waste water can be reduced by biological means with the same degree of success as for domestic waste water (communal waste water), or

which is treated in a river clarifying basin and whose origin corresponds to numbers 1 or 2.

B) General requirements
Article 3 paragraph (1) shall not apply.

C) Requirements for waste water at the point of discharge
(1) The following requirements apply to waste water at the point of discharge into the water body:

Samples according
to size categories of
the waste water
treatment plants
Chemical oxygen demand
Ammonia nitrogen
Total nitrogen as the sum of ammonia, nitrite and nitrate nitrogen (Ntot) Total phosphorous
mg/l mg/l mg/l mg/l mg/l
Qualified random sample or 2-hour composite sample
Size category 1
Less than 60 kg/d
BOD5 (raw)
150 40
Size category 2
60 to 300 kg/d
BOD5 (raw)
110 25
Size category 3
greater than 300 up
to 600 kg/d BOD5
90 20 10
Size category 4
greater than 600 up
to 6000 kg/d BOD5
90 20 10 18 2
Size category 5
greater than 6000
kg/d BOD5 (raw)
75 15 10 13 1

The requirements apply to ammonium nitrogen and total nitrogen, at a waste water temperature of 12° C and above in the effluent from the biological reactor of the waste water treatment plant. The 12° C threshold may be replaced by the following time limit: from 1st May to 31st October. The water discharge licence may stipulate a higher concentration for total nitrogen, of up to 25 mg/l, provided the reduction of the total nitrogen load is at least 70 per cent. The reduction shall refer to the ratio between the nitrogen load in the influent and that in the effluent, over a representative period of time not exceeding 24 hours. The load in the influent shall be based on the sum of organic and inorganic nitrogen.

(2) The allocation of a discharger to one of the size categories specified in paragraph (1) above shall depend on the assessment levels of the waste water treatment plant, using the BOD load of the untreated waste water – BOD (raw) – as a basis. In cases where only the BOD level of the sedimented sewage is used as a basis for the assessment level of a waste water treatment plant, the following levels shall be decisive for classification:

Size category 1: less than 40 kg/d BOD (sed.)
Size category 2: 40 to 200 kg/d BOD (sed.)
Size category 3: greater than 200 kg/d to 400 kg/d BOD (sed.)
Size category 4: greater than 400 kg/d to 4,000 kg/d BOD (sed.)

Size category 5: greater than 4,000 kg/d BOD (sed.)
(3) In sewage lagoons designed for a detention time of 24 hours or more, where a sample is clearly coloured due to algae, the COD and BOD shall be determined from a sample not containing any algae. In such cases, the levels specified in paragraph (1) above shall be reduced by 15 mg/l for COD and by 5 mg/l for BOD.

(4) In the case of small discharges within the meaning of Article 8 in conjunction with Article 9 (2) second sentence of the Waste Water Charges Act (Abwasserabgabengesetz), the requirements for size category 1, pursuant to paragraph (1) above, shall be deemed to have been met if a waste water treatment plant authorised by a general building-inspectorate approval, by a European-oriented technical approval pursuant to provisions of the Bauproduktengesetz (Act on Construction Products) or otherwise authorised in accordance with Land Law is installed and operated in keeping with the relevant authorisation. The relevant authorisation must also set forth the requirements for proper function of the facility, with respect to installation, operation and maintenance of the facility.

(5) For small discharges within the meaning of Article 8 in conjunction with Article 9 (2) second sentence of the Waste Water Charges Act (Abwasserabgabengesetz), the Länder may establish different requirements if connection to a public wastewater treatment facility is expected in the near future.

Appendix 51
Qualified random sample
or 2-hour composite sample
Chemical Oxygen Demand (COD)
Five-day biochemical oxygen demand (BOD)
Total nitrogen as the sum of ammonia, nitrite and nitrate nitrogen (Ntot)
Total phosphorous
Total hydrocarbons
Nitrogen from nitrite (NO-N)
Toxicity to fish eggs (Tegg)

(2) In the case of waste water whose chemical oxygen demand content (COD) prior to treatment is assumed to be in excess of 4000 mg/l, in derogation of paragraph (1) above, an effluent level for COD in the qualified random sample or 2-hour composite sample shall apply which is equivalent to at a reduction in COD of at least 95 per cent. The reduction in COD shall refer to the ratio between the contaminant load in the influent and that in the effluent from the waste water treatment plant over 24 hours. For the contaminant load of the influent, the capacity utilisation of the plant on which the permit is based shall be decisive. The scope of the reduction shall be evaluated on the basis of the dimensioning and mode of operation of the waste water treatment plant.

(3) The requirement for total hydrocarbons shall apply to the random sample. It shall not apply to waste water from the storage of domestic waste.

(4) The requirement for total nitrogen shall apply at a waste water temperature of 12 °C and above in the effluent from the biological reactor of the waste water treatment plant. A value specified for total nitrogen shall also be deemed to have been met in accordance with the definition of “total bonded nitrogen (TNb)”. A higher concentration of up to 100 mg/l may be conceded for total nitrogen in the water discharge licence, provided the reduction in the nitrogen load is at least 75%. The reduction shall refer to the ratio between the nitrogen load in the influent and that in the effluent, over a representative period of time not exceeding 24 hours. Total bonded nitrogen (TNb) shall be used as a basis for calculating the loads.

D) Requirements for waste water prior to blending
(1) The following requirements apply to the waste water prior to blending with other waste water:

Qualified random sample
or 2-hour composite sample
Adsorbable organically bound halogens (AOX)
Chromium VI
Cyanide, easily released

In the case of AOX, chromium VI, easily released cyanide and sulphide, the values for the random sample shall apply.

(2) Waste water, except for waste water from installations for biological waste treatment, may be blended with other waste water for the purpose of joint biological treatment only if at least one of the following requirements is expected to be met:

1. In determination of the toxicity to fish eggs, luminescent bacteria and daphnia of a representative wastewater sample, the following values are not exceeded, following execution of an elimination test with a biological, laboratory-scale continuous-flow treatment system (such as a system in keeping with DIN 38412 L 26):

  • Toxicity to fish eggs (Tegg) = 2
  • Toxicity to daphnia (TD) = 4
  • Toxicity to luminescent bacteria (TL) = 4

Via such measures as nitrification in the laboratory-type biological sewage treatment plant or pH value maintenance, steps are taken to ensure that the Tegg value is not exceeded due to ammonia (NH3). The waste water may be diluted as required to start up the laboratory-type biological sewage treatment plant. In the event of a lack of nutrients, nutrients may be added. During the test phase, no dilution water may be added.

2. A DOC elimination level of 75% in accordance with number 408 of the Annex “Analysis and measurement procedures” is achieved.

3. Prior to joint biological treatment with other waste water, the waste water already indicates a COD concentration level of less than 400 mg/l.

ADR Ordinance

The acronym ADR or AdR stands for:

  • Accord européen relatif au transport international des marchandises Dangereuses par Route, in English, European Agreement concerning the International Carriage of Dangerous Goods by Road

The ADR also regulates

  • the classification of goods to be transported as dangerous goods and the relevant safety measures
  • labelling (marking) and documentation such as transport documents and written instructions (TREMCARD) for transport of dangerous goods
  • the construction of containers, tanks, vehicles for transport of dangerous goods
  • exemptions related to compliance with the ADR regulations
  • multi-modal transport of dangerous goods (by road – rail, ship or aircraft)

The ADR also stipulates that

  • in many cases, the driver must have a dangerous goods license
  • all persons involved in handling and transportation must demonstrate specialist knowledge in the provisions for carriage of dangerous goods
  • the companies transporting dangerous goods must have a Dangerous Goods Safety Adviser

Safety obligations, documentation and instructions
The key content of the ADR is documentation of the transport process, clarification of the safety obligations of the participants and instructions to the parties involved, from shipper via packing agent and carrier and the recipient of the shipment, up to the emergency chain in cases of damage.

The ADR requires labelling of dangerous goods transport packaging and vehicle with labels for dangerous goods, and on vehicles, also the hazard panel (orange warning panel) with the hazard identification number (Kemler) and the UN number.

Personal protective equipment
This is stipulated in the written instructions. Every member of the vehicle crew must carry personal protective equipment. Personal protective equipment includes:

  • eye protection (e.g. protective goggles)
  • a pair of protective gloves
  • portable lighting apparatus
  • a warning vest
  • an emergency escape mask (only required for danger label numbers 2.3 and 6.1)

The vehicle must often be approved for the transport of dangerous goods (tank-vehicles and vehicles for the transportation of explosive substances and articles containing explosives) and

  • a fire extinguisher depending on the weight of the vehicle
  • two self-standing, reflective warning signs (two flashing lights or two warning triangles or two pylons – traffic warning cone)
  • wheel chocks, suitable to the maximum mass of the vehicle and the diameter of the wheel (for tractors and if available for trailers or semi-trailers)
  • if exceeding the exemption thresholds warning plates (front and rear) and if necessary, labels for dangerous goods on the right and left and on the rear of the vehicle
  • eye rinsing liquid (not required for danger label numbers 1 and 2)
  • a shovel, a drain seal and a plastic collecting container (only required for danger label numbers 3, 4.1, 4.3, 8 and 9)
Discharge limits

See: Appendix 1
See: Appendix 51


The chemical oxygen demand, also abbreviated as COD, is a so-called sum parameter, since no individual compounds can be quantified with it. It is determined by means of oxidation of waste water contents by potassium dichromate and measures the oxygen demand for oxidizing a majority of organic substances. If there are also oxidizable inorganic compounds, like sulphites, in the waste water, these are also registered as COD. For the chemical oxygen demand, a value of 120 grammes per inhabitant and day is assumed.


The BOD value, the biochemical oxygen demand during a measured time of five days at 20° C, measures the oxygen demand that arises due to the oxidation of organic substances by aerobic micro-organisms. It is a so-called sum parameter, since the degradation of single compounds cannot be determined with it.

The bacterial oxidisation of ammonia (NH), ammonium (NH₄₊) and nitrite (NO) to nitrate (NO₃₋), called nitrification, should not be measured and is blocked during the measurement by an inhibitor, such as allylthiourea (ATU) or sodium hydroxide pellets.

A usual value for BOD is 60 g per inhabitant and day. Of this, about 20 g can be removed in the primary clarifier by means of sedimentation. The following conditions are necessary to determine BOD:

  • The prepared sample must contain sufficient oxygen during the entire consumption period, that is a minimum of 2 mg/l.
  • The prepared sample must contain sufficient bacteria. They are abundant. in normal waste water. Bacteria must be added in special industrial effluent (e.g. landfill leachate purification). Domestic water is “inoculated” with 0.3 ml/l of the prepared sample.
  • The prepared sample must contain sufficient nitrogen and phosphate as nutrients.
  • The prepared samples must be kept for five days in the dark with the temperature kept stable at 20° C, preferably in a thermostatically controlled cabinet.
Directive 91/271/EEC

This Directive concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors. Its objective is to protect the environment from the adverse effects of this waste water. Industrial waste water entering collecting systems as well as the discharge of waste water and disposal of sludge from urban waste water treatment plants should be subject to general rules or regulations and/or specific authorisations.

The Directive contains a binding timetable for the Member States to equip communities that meet the criteria of the Directive with municipal waste water collection and treatment plants. The main deadlines are as follows:

  • 31st December 1998: All agglomerations whose “population equivalent”* (p.e.) is above 10,000 and whose waste water is discharged into sensitive areas, must have a collecting system and a system for thorough treatment;
  • 31st December 2000: All agglomerations of more than 15,000 p.e. and whose waste water is not discharged into sensitive areas must have a collecting system and a treatment system, which is able to comply with the conditions listed in the table of Annex I;
  • 31st December 2005: all agglomerations with p.e. between 2,000 and 10,000, whose waste water is discharged into sensitive areas, and all agglomerations with p.e. between 2,000 and 15,000, who do not discharge wastewater into such areas must have a collecting system and a treatment system.

Member States shall, in accordance with Annex II identify sensitive and less sensitive areas into which the treated water is discharged. These lists must be updated at regular intervals. The treatment of municipal waste water depends on the sensitivity of the water into which it is being discharged.

The Directive contains specific requirements for the disposal of biodegradable industrial waste water from plants belonging to certain industrial sectors, which does not enter urban waste water treatment plants before discharge into receiving waters.
The Member States shall be responsible for the monitoring of discharges from waste water treatment plants and the receiving waters. They shall ensure that their competent authorities publish a situation report every two years. This report must be forwarded to the Commission.

Member States must set-up national programmes for the implementation of this Directive and must present them to the Commission.

The Directive also provides for exemptions and temporary derogations.

Directive 98/15/EC

This Directive clarifies the rules relating to discharges from urban waste water treatment plants in order to put an end to differences in interpretation by the Member States.

This Directive specifies that:

  • the option of using daily averages for the total nitrogen concentration applies both to agglomerations of 10,000 – 100,000 p.e. and to those of more than 100,000 p.e.;
  • the condition concerning the temperature of the effluent in the biological reactor and the limitation on the time of operation to take account of regional climatic conditions only apply to the “alternative” method using daily averages;
  • use of the “alternative” method must ensure the same level of environmental protection as the annual mean technique.
Urban waste water

Waste water from residential settlements and services which originates predominantly from the human metabolism and from household activities (domestic waste water) or a mixture of domestic waste water with waste water which is discharged from premises used for carrying on any trade or industry (industrial waste water) and/or run-off rain water.


The enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned.

Population equivalent

A measure of pollution representing the average organic biodegradable load per person per day: It is defined in Directive 91/271/EEC as the organic biodegradable load having a five-day biochemical oxygen demand (BOD₅) of 60 g of oxygen per day.

Waste water

The term waste water is defined in the Federal Republic of Germany Article 54 para. 1 Water Management Act (WHG) of 31 July 2009 (Federal Law Gazette I S. 2585).

According to this, waste water is water whose properties have been changed by domestic, commercial, agricultural or other usage and the water drained together with it during dry weather conditions (polluted water), as well as water running off and collected from built-up or paved or asphalted surfaces following precipitation (rain water). Liquids released and collected from facilities designed for the treatment, storage and depositing of waste shall also be deemed to be polluted water.

Waste water treatment

Source: Wikipedia