Urban waste water treatment

Indicator Specification
Indicator codes: CSI 024 , WAT 005
Created 07 Oct 2004 Published 07 Apr 2005 Last modified 12 Oct 2017
9 min read
The indicator on waste water treatment CSI 024 is defined as the percentage of the population connected to sewage collection systems as well as primary, secondary and tertiary waste water treatment plants. The amount of the waste water is expressed as population equivalents (p.e.). The indicator illustrates: development of waste water collection and treatment in Europe since the 1970s; development of more stringent waste water treatment; level of waste water treatment in large cities (agglomerations >150 000 p.e.) in the EU.  

Assessment versions

Published (reviewed and quality assured)

Rationale

Justification for indicator selection

Wastewater from households and industry represents a significant pressure on the water environment because of the loads of organic matter and nutrients as well as hazardous substances. With high levels of the population in EEA member countries living in urban agglomerations, a significant fraction of wastewater is collected by sewers connected to public wastewater treatment plants. The level of treatment before discharge and the sensitivity of the receiving waters determine the scale of impacts on aquatic ecosystems. The types of treatments and conformity with the directive are seen as proxy indicators for the level of purification and the potential improvement of the water environment.

Primary (mechanical) treatment removes part of the suspended solids, while secondary (biological) treatment uses aerobic or anaerobic micro-organisms to decompose most of the organic matter and retain some of the nutrients (around 20 - 30 %). Tertiary (advanced) treatment removes the organic matter even more efficiently. It generally includes phosphorus retention and in some cases nitrogen removal. Primary treatment alone removes no ammonium whereas secondary (biological) treatment removes around 75 %.

The indicator tracks the success of policies to reduce pollution from wastewater by describing the trends in the percentage of the population connected to public wastewater treatment plants with different levels of purification.

Scientific references

  • No rationale references available

Indicator definition

The indicator on waste water treatment CSI 024 is defined as the percentage of the population connected to sewage collection systems as well as primary, secondary and tertiary waste water treatment plants. The amount of the waste water is expressed as population equivalents (p.e.). The indicator illustrates:

  1. development of waste water collection and treatment in Europe since the 1970s;

  2. development of more stringent waste water treatment;

  3. level of waste water treatment in large cities (agglomerations >150 000 p.e.) in the EU.

 

Units

Percentages of population connected to primary, secondary and tertiary wastewater treatment.

Policy context and targets

Context description

The Urban Waste Water Treatment (UWWT) Directive (91/271/EEC) prescribes the level of treatment required before discharge to surface water. It requires Member States to provide all agglomerations of more than 2 000 population equivalents (p.e.) with collecting systems. Primary (mechanical) and secondary treatment (i.e. biological treatment) must be provided for all agglomerations of more than 2 000 p.e. discharging into fresh waters. Special requirements with intermediate deadlines depending on the sensitivity of the receiving waters are placed on agglomerations of more than 10 000 p.e. with various size classes of agglomerations. The performance of the treatment is assessed using five different determinands (Biochemical oxygen demand - BOD, Chemical oxygen demand - COD, Total suspended solids - TSS, Total nitrogen - Ntot and Total phosphorus - Ptot).

For agglomerations smaller than described above and those equipped with a collecting system, the treatment must be “appropriate”, meaning that the discharge allows the receiving waters to meet the relevant quality objectives.

The UWWTD, adopted in 1991, is also a basic measure under the Water Framework Directive (WFD). The WFD requires the estimation and identification of significant point and diffuse source pollution, in particular by substances listed in Annex VIII, from urban, industrial, agricultural and other installations and activities, based, inter alia, on information gathered i.a. under Articles 15 and 17 UWWTD. From the substances listed in Annex VIII WFD, the following are important for CSI 024:

  • substances which have an unfavourable influence on the oxygen balance (and can be measured using parameters such as BOD, COD, etc.),
  • materials in suspension, and
  • substances which contribute to eutrophication (in particular, nitrates and phosphates).

Member States should thus take the necessary steps to collect these data. Reducing pollutants stemming from waste water is one of the key challenges for reaching good ecological and good chemical status of surface waters, as required by the WFD.

Targets

The Urban Waste Water Treatment Directive aims to protect the environment from the adverse effects of urban waste water discharges. It prescribes the level of treatment required before discharge and should have been fully implemented in the EU-15 countries by 2005 and in the ten new Member States by 2008 - 2015. The directive requires Member States to provide all agglomerations of more than 2 000 population equivalent (p.e.) with collecting systems and all waste waters collected to be provided with appropriate treatment by 2005. Secondary treatment (i.e. biological treatment) must be provided for all agglomerations of more than 2 000 p.e. that discharge into fresh waters, while more advanced treatment (tertiary treatment) is required for discharges into sensitive areas. To help minimise pollution from various point sources, the Integrated Pollution Prevention and Control directive, which came into force 1996, has a set of common rules on permitting for industrial installations.

The achievements through the UWWTD and the IPPC directive have to be seen as an integrated part of objectives under the Water Framework Directive (WFD) which aim at a good chemical and biological status for all waters by 2015.

Related policy documents

  • COM(2004) 248 final
    Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment, as amended by Commission Directive 98/15/EC of 27 February 1998
  • Council Directive (91/271/EEC) of 21 May 1991
    Council Directive of 21 May 1991 concerning urban waste water treatment (91/271/EEC)
  • Urban wastewater treatment summary report
    Summary report on: the identification of sensitive areas by the Member States; the measures implemented by the Member States with the view to the deadline of 31 December 1998; wastewater treatment in major cities; verification of the identification of sensitive areas by the Commission.

Key policy question

How effective are existing policies in reducing discharges of nutrients and organic matter into surface waters?

Specific policy question

What is the level of urban waste water treatment in large cities in the EU?

Methodology

Methodology for indicator calculation

The CSI 024 is based on data from Eurostat, which is then aggregated into groups of countries. Percentages connected to each treatment type, weighted by total population in each country were used from Eurostat tables. Compared to previous versions of the indicator, the time steps have been regularised and the number of countries reported in each region in Figure 1 has been kept constant across the time period.

 

Methodology for gap filling

The most recent year reported was used for gap filling e.g. 2013 data used for 2014. This approach used for up to 9 years gap filling.

 

Methodology references

No methodology references available.

Data specifications

EEA data references

External data references

Data sources in latest figures

Uncertainties

Methodology uncertainty

For the assessment shown in Figure 1, countries have been grouped to show the relative contribution on a larger statistical basis. So as to provide a complete and comparable dataset over the time period, some countries have been omitted from the European overview.

Regional results are biased towards countries with the largest population (e.g. Turkey constitutes about 70 % of the inhabitants in the whole South-eastern European region).

 

Data sets uncertainty

Eurostat data sometimes provides an incomplete picture of connected or treated inhabitants (e.g. the percentage of population connected to waste water systems is given, but the percentage where the waste water is collected without treatment is missing).

Slovakia reported much of its waste water treatment as “not specified” which leads to a probable under-estimate of the amount of treatment applied in that country.

 

 

Rationale uncertainty

Data gained from the UWWT Directive focuses on the performance of the treatment plant alone. However, waste water treatment systems could also include sewer networks with storm water overflows and storage which are complex and  overall performance is difficult to assess. In addition to the treatments covered by the UWWT Directive, there are other possible treatments, mostly industrial, but also independent treatments of smaller settlements outside urban agglomerations not included in UWWT Directive reporting. Compliance with the levels defined in the directive therefore does not guarantee that there is no pollution due to urban waste water.

In addition, urban waste water treatment (primary, secondary and tertiary, as described above) is the main waste water treatment used across the EEA area, but there are other possible treatments classified as “Other Waste Water Treatment”, which are mostly industrial or independent treatments. Furthermore, there are differences in how countries have interpreted and implemented the Directive leading to differences in the data reported. In particular, there are variations in the definitions of different classes of treatment between countries (classes based on performance or on design capacity and tertiary treatment for N, P or organic matter) that in turn lead to differences in the level of purification attributed by the countries to the classes. These differences emphasise the problem of using types of treatment plant as a proxy for the level of purification.

 

 

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Caroline Whalley

Ownership

European Environment Agency (EEA)

Identification

Indicator code
CSI 024
WAT 005
Specification
Version id: 1

Frequency of updates

Updates are scheduled every 2 years

Classification

DPSIR: Response
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)

Related content

Data references used

Data used

Latest figures and vizualizations

Relevant policy documents

European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Denmark
Phone: +45 3336 7100