About UNEP
United Nations Environment Programme
Division of Technology, Industry and Economics
top image
space space space
Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

6.0.4 what is considered the "state of tht art" in Western Europe?

The state of the art may be the latest in scientific discovery. However, in European wastewater practice, the state of the art is considered a technology, process and/or an operation which will be best suited to achieve a stated objective in today´s context, e.g. to reduce the BOD of the wastewater to 25 mg/L or by 80%. This implies prior successful testing of the technology in comparison to similar ones. State of the art implies further, that a majority of the experts in the field would accept it as a criterion and that it may undergo changes in accordance with changes as regards the objectives to be achieved, the resources available, and the time frame for action.

Accordingly, in defining the state of the art, the following are considered:

  • Comparable technologies, processes and/or operations which have been tested successfully in the recent past.
  • Technical advancement and changes in the scientific understanding.
  • Economic feasibility.
  • Time frame for action.
  • Type and quantity of the wastewater discharged.

As will be discussed in Section 6.6, water pollution legislation of the European Union is based on the "best available technology (bat)" Bat and the state of the art are comparable concepts (Dohmann 1996): on the one hand, the state of the art is the most efficient and advanced technology which is available and practical, whereas, on the other hand, the best available technology is the most efficient and advanced technology which is considered practical to prevent, or, if this should not be possible, to minimize the emission of a pollutant into the environment. Both are not exclusively technical-scientific concepts. In European practice, they include a strong element of practicability and feasibility as measured against the objectives set forth in the water pollution control legislation of the European Union.

It also follows that bat and the state of the art are based not simply on the scientific advancement but rather on the professional judgement of the experts and their professional organizations. It is important, further, that bat and the state of the art represent a majority view of the experts rather than that of an individual scientist or institution. They are not up-dated by continuous process in accordance with scientific progress but rather from time to time whenever one of the four variables has undergone significant change, i.e.:

  • The objective to be achieved.
  • The scientific and technical understanding.
  • The resources available.
  • The time frame for action which may be imposed.

Keeping these matters under review and deciding on the timeliness of up-dates is one of the functions of the professional water pollution control organizations which exist in most European countries as well as their Europe-wide professional umbrella the European Water Association (EWA); see also Sections 6.2.1-6.2.2 and addresses in Section 6.10. Their reviews take place in consultation with the regulatory agencies concerned.

6.0.5 Common approaches to the choice of technology

In the developing world, the choice of technology for wastewater and stormwater management is a complicated matter. Many factors need to be considered in addition to the technical ones and the uncertainties are great. In Western Europe, this is more straightforward. On the one hand, there is no longer a dispute over the need and the feasibility of high quality systems for the collection of wastewater and stormwater and for wastewater treatment. On the other hand, uncertainties are minor in comparison with those encountered in the developing countries. Demographic and other developmental information; topographic, hydrological, and environmental data is largely available; and the price elasticity of wastewater and stormwater management is high. Further, there is an overwhelming choice of manufacturer's equipment, maintenance tools, laboratory and monitoring apparatuses, and software for management and operation.

Another feature in the choice of technology in Western Europe is that few projects start from scratch. More often than not, decisions have to be made and technology chosen for extensions and/or the up-grading of existing systems rather than for new ones. In many cases, planners can plan and design on the basis of the performance of existing systems, and their task is then "simply" to extrapolate into the future rather than to consider fundamental alternatives.

Some of the most important factors are briefly discussed below:

  • Coverage, degree of treatment, and timeframe: The basic decisions with respect to coverage, degree of treatment, and timeframe have already been taken in the context of EU Directive 91/271 of 1991 (EEC 1991). Communities with more than 2000 pe are targeted to have collection systems by 2000 or 2005 depending on their size. Normally, they must have secondary treatment but in sensitive areas, tertiary treatment is to be provided for communities with more than 10000 pe. Tables 6.12 and 6.13 exhibit the targets and the effluent standards which must be met.
  • Separate vs. combined collection systems: Separate systems are generally preferred although they are usually more expensive than combined. Compatibility with existing systems or system components is important. More than half of the collection systems in Europe are combined. As much as 80% of the built up areas may be served by combined systems in some countries, and in practically no case less than 50%. The separation of combined systems is expensive. Nevertheless, the use of separate systems is likely to be continued, not least for new developments in residential areas provided that safeguards exist to minimize the risk of wrong connections. A major decision criteria is the pollution discharged at times of rain. The above-mentioned EU Directive 91/271 stipulates that the design, construction and maintenance of collection systems shall be undertaken in accordance with the best technical knowledge but not entailing excessive costs. Thus, the choice of technology and system design are governed by environmental and economic requirements, and the intricate task of integrating and/or expanding mixed systems of combined and separate components. The matter of stormwater overflows and their contribution to environmental pollution is discussed in Section 6.2.2.
  • Treatment technology: The degree of treatment required has already been discussed above. Within this framework, the choice concerns the processes of secondary and tertiary treatment and the associated costs. These matters are discussed respectively in Sections 6.3.2 and 6.9.
  • Industrial wastewater entering urban wastewater systems: Not all industrial waste can be discharged directly into a receiving water. In Western Europe, almost 60% enter urban wastewater collection systems and treatment plants. The municipalities are obliged to receive the waste but authorization is given subject to pre-treatment and charges levied in accordance with the quantity and the quality of the waste. For the State Members of the EU, Council Directive 91/271 stipulates the requirements which industrial wastewater entering an urban collection system and treatment plants shall meet ( see Section 6.6.1).
  • Cost: The price elasticity of sewer charges is high in Europe. Nevertheless, there are limits to be observed. The matter of cost and cost recovery will be discussed in Section 6.9.
  • Economy of scale: The European Waste Water Group (EWWG 1995) observes that wastewater treatment has a substantial economy of scale. The cost per person of a large treatment plant serving 100000 pe is about one fifth compared with that of a small plant serving 2000 pe. It is further observed that a large proportion of the treatment plants necessary in Western Europe will serve relatively small communities; therefore, it will be economical to opt for regional or other forms of joint schemes and/or link small agglomerations to larger systems in the region. In contrast, collecting system do not have the same economy of scale because the length of the network is proportional to the number of properties to be connected.
  • Adherence to technical standards: A great variety of norms and technical standards for the collection systems and treatment plants exist in Western Europe. They have been issued by professional associations and/or standard institutions. Some are binding while others are recommended practice. Technology choice in European practice is firmly related to these standards as is best exhibited by the authority accorded to them in the process of giving consent for the construction and/or operation of a sewerage system or a treatment plant. However, it would be overstating the case if this were to imply that the design and/or operation of a system are straight-jacketed by these standards. Nevertheless, technology choice is more governed by standards in Western Europe than would be conceivable in the developing countries of the world. The matter of standardization is discussed in some detail in Sections 6.0.6 and 6.6.1.
  • Manufacturer's choice: The variety of equipment and services offered by European manufacturers and other supplier is a key variable in the choice of technology. The best source of information is the International Trade Fair for Environment and Sanitation (IFAT) which is taking place in Munich every three years and is the largest such gathering world-wide. It covers wastewater, water supply, waste, street cleansing, laboratory technology, monitoring and control, and various types of services. IFAT 12 took place in May 1999 and IFAT 13 is scheduled for May 2002. Subjects covered in 1999 included sewers pipes and fittings; sewer construction, inspection, monitoring and rehabilitation: pumping and lifting; sewage treatment processes (primary, secondary and tertiary); sludge treatment, stabilization, recycling and disposal; laboratory technology and instrumentation; monitoring and control; energy management and the handling of residues (IFAT 1999).

6.0.6 Technical standards and state of the art reviews elaborated by professional associations

Professional associations exist in most of the countries of Western Europe. At the European level, they are integrated in the former European Water Pollution Control Association (EWPCA) which has been renamed the European Water Association (EWA). They are listed in Section 6.10 and are the most important source of information concerning wastewater and stormwater technology and management in Europe. The national member organizations of EWA comprise more than 40 000 Experts in wastewater and stormwater management as well as many sewage works operational organizations, equipment manufacturers, and regulatory. The Association has a Scientific Committee which keeps a watch on technical and scientific progress and helps evaluate the timeliness of review and the up-dating bat and the state of the art. It is basically at the national level that the professional organizations and national administrations undertake the up-dates and publish them in the languages of their members. It is impossible to present a full account of this work in the present Overview. However below, reference is made to some of the organizations which publish in English, French or German since one of these languages will be understood in most the countries of the region. They are the Association Général des Hygiénistes et Techniciens Municipaux (AGHTM) and the Minist“re de l´Aménagement du Territoire et de l´Environnement (MATE) in France, the Chartered Institution of Water and Environmental Management (CIWEM) and the Water Research Centre (WRc) in the UK and the German Water Pollution Control Association (ATV) in Germany.

The AGHTM is a professional centre for the exchange of technical, scientific and administrative information related to all aspects of urban and rural engineering. Further, it promotes studies and research and participates in developing regulations and advisory services. The Association publishes and monthly magazine, and holds a congress and specialized conferences etc. As its name implies, the MATE acts in a combined capacity both governmental and technical which is in line with traditions in France, and is linked with many other organizations in France, including the Office International de l´Eau OIEAU, a non profit association under French Law. MATE convenes conferences and publishes guidelines; OIEAU maintains a sizable documentation service (EAUDOC) and organizes training. CIWEM is strictly technical and publishes introductory books, handbooks and manuals which reflect the state of the art, e.g. handbooks on wastewater practice in the UK (4 volumes) and sewage sludge (4 volumes) Aqualine is a documentation service maintained by the Water Research Center (WRc) which also serves as the Topic Center on Inland Water of the European Environment Agency. The ATV´s publishes a series of handbooks on wastewater practice ( 6 volumes) and issues Technical Standards and Advisory Leaflets currently covering more than two hundred subjects related to sewerage systems, sewage treatment, sludge, and industrial wastewater; many of these are available in English and an increasing number also in other languages. ATV also maintains a comprehensive training programme at all levels (see also Section 6.7.2).


      Main Menu


  • Brochure
  • IETC Brochure

  • International Year of Forests
  • International Year of Forests

  • World Environment Day
  • ??????

  • UNEP Campaign
  • UNite to Combat Climate Change