Urban waste water treatment

Indicator Specification
Indicator codes: CSI 024 , WAT 005
Created 07 Oct 2004 Published 07 Apr 2005 Last modified 08 Nov 2017
9 min read
The indicator on urban waste water treatment, CSI 024, collects data on the percentage of the population connected to sewage collection systems, as well as on the prevalence of primary, secondary and tertiary urban waste water treatment plants. The amount of urban waste water treated is expressed as population equivalents (p.e.). The indicator illustrates: the development of urban waste water collection and treatment in Europe since the 1970s; the development of more stringent urban waste water treatment practices; the level of urban waste water treatment in 'big cities' (agglomerations of > 150 000 p.e.) in the EU.  

Assessment versions

Published (reviewed and quality assured)

Rationale

Justification for indicator selection

Waste water from households and industry represents a significant pressure on the aquatic 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 urban waste water is collected by sewers connected to public waste water treatment plants. The level of treatment before discharge and the sensitivity of the receiving waters determine the scale of the impacts on aquatic ecosystems. The proportion of the population connected to urban waste water treatment plants and the types of treatments used are seen as proxy indicators of the level of purification and the potential for improvement of the water environment.

Primary (mechanical) treatment removes some of the suspended solids, while secondary (biological) treatment uses aerobic or anaerobic microorganisms to decompose most of the organic matter and retain some of the nutrients (around 20-30 %). Tertiary (advanced) treatment removes 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 % of ammonium.

This indicator tracks the success of policies aimed at reducing pollution from waste water by describing the trends in the percentage of the population connected to urban waste water treatment plants with different levels of purification.

Scientific references

  • No rationale references available

Indicator definition

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

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

  2. the development of more stringent urban waste water treatment practices;

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

 

Units

The percentages of the population connected to primary, secondary and tertiary urban waste water treatment facilities.

Policy context and targets

Context description

The main objective of the UWWT Directive (91/271/EEC), and equivalent national legislation for non-EU countries, is to protect surface waters from the adverse effects of waste water discharges. The UWWT Directive prescribes the level of treatment required before discharge to surface waters. It requires Member States to provide all agglomerations of more than 2 000 p.e. with collecting systems. Primary (mechanical) and secondary (i.e. biological) treatments must be provided for all agglomerations of more than 2 000 p.e. that discharge 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 those described above and equipped with a collecting system, the treatment must be 'appropriate', meaning that the discharge must allow the receiving waters to meet the relevant quality standards.

The UWWT Directive, 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 the substances listed in Annex VIII, from urban, industrial, agricultural and other installations and activities, based, inter alia, on information gathered, for instance, under Articles 15 and 17 of the UWWT Directive. Based on the substances listed in Annex VIII WFD, the following are important for this indicator:

  • substances that have an unfavourable influence on oxygen balance (and can be measured using parameters such as BOD, COD, etc.);
  • materials in suspension;
  • substances that 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 of reaching good ecological and good chemical status of surface waters, as required by the WFD.

Targets

The UWWT Directive (91/271/EEC) 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. For the newer Member States (i.e. the EU-13), staged transition periods were set within the Accession Treaties which, in principle, did not extend beyond 2015. However, in Romania, smaller agglomerations (with less than 10 000 p.e.) should comply with the directive by the end of 2018, and Croatia has different transition periods, from 2018 to 2023.

Under the directive, EU-15 Member States were required to provide all agglomerations of more than 2 000 p.e. with collecting systems and all waste waters collected had 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.


The achievements resulting from the UWWT Directive should be seen as an integral part of achieving good status for all waters under the WFD. 

 

        

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 policies aimed at improving urban waste water treatment at reducing discharges of nutrients and organic matter into surface waters?

Specific policy question

What levels of urban waste water treatment are applied in 'big cities' in the EU?

Methodology

Methodology for indicator calculation

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

A p.e. of 1 is equivalent to an organic biodegradable load having a 5-day BOD of 60 g per day.

'Big cities' is a term used in the UWWT Directive to identify cities of at least 150 000 p.e. or agglomerations responsible for large waste water discharges.

Methodology for gap filling

Gap filling was undertaken on the basis that once an urban waste water infrastructure had been put in place, it was likely to be used in subsequent years. Therefore, any gaps were filled with data from the most recent year reported, e.g. 2004 data carried forward to 2005. This approach was used for up to 9 years of gap filling, e.g. 2004 data could be carried forward to up to 2013.

 

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. To provide a complete and comparable data set over the 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 of the entire south-eastern Europe region).

 

Data sets uncertainty

Data reported to Eurostat sometimes provide an incomplete picture of inhabitants connected to waste water treatment (e.g. the percentage of the population connected to urban waste water systems is given, but the percentage for which the waste water is collected without treatment is missing).

Slovakia reported much of its urban waste water treatment as 'not specified', which is likely to lead to an underestimate of the percentage of treated waste water in that country.

 

 

Rationale uncertainty

Data gained from the UWWT Directive focuses on the performance of the treatment plant alone. However, urban waste water treatment systems could also include sewer networks with storm water overflows and storage, which are complex and therefore 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 or 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 UWWT 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 design capacity and tertiary treatment for nitrogen, phosphorus or organic matter) that, in turn, lead to differences in the level of purification attributed by the countries to the different 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