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Indicator Assessment
The treatment of urban waste water is fundamental to ensuring public health and environmental protection. Urban waste water treatment in all parts of Europe has improved over the last 30-40 years.
In 2017, most European countries collected and treated sewage to tertiary level from most of their population. In EU-27 countries (EEA 2020), 69 % of the population were connected to tertiary level treatment and 13 % to secondary level treatment.
Countries where less than 80 % of the population were connected to public urban waste water treatment systems were Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Ireland, Italy, Lithuania, Poland, Romania, Serbia, Slovakia and Slovenia.
The treatment of urban waste water from our homes and workplaces is fundamental to ensuring public health and environmental quality. The main objective of the Urban Waste Water Treatment (UWWT) Directive (91/271/EEC), and equivalent national legislation for non-EU countries, is to protect the environment — specifically surface waters — from the adverse effects of waste water discharges — such as oxygen-consuming organic pollution, which degrades aquatic life — and microbiological contamination with pathogens. This is achieved through the collection and treatment of waste water in settlements and areas where population and economic activity are sufficiently concentrated (agglomerations), with the polluting load generated expressed as a population equivalent (p.e.). The UWWT Directive covers agglomerations over 2 000 p.e. In most cases, it stipulates that waste water must be subject to biological treatment (secondary treatment), but in catchments with particularly sensitive waters, such as those suffering from eutrophication, more stringent (tertiary) waste water treatment may be required to substantially reduce nitrogen and phosphorus pollution.
The installation of waste water treatment facilities first requires the set-up of a sewage collecting system, followed by the provision of facilities to treat the collected waste water. Where there is a low proportion of a population connected to waste water treatment facilities, it may be because of a lack of financial resources (or priority) for providing the sanitation services, low population density, or to high a proportion of the population living outside agglomerations. Where people live in scattered communities, individual sanitation systems (e.g. package waste water treatment plant, septic tanks) may be the most feasible solution. Such systems can provide treatment efficiencies that are similar to those of larger urban waste water treatment plants.
The indicators used in this assessment to measure discharged loads of organic matter and nutrients from urban waste water treatment plants to European surface waters are:
Compared with earlier versions of this indicator, some changes in historical data have been included owing to corrections made by countries in the Eurostat data set.
Note that the data used in Figures 1 and 2 use Eurostat data which are reported for the national population, while the UWWT Directive (used in Figure 3) uses data reported for urban settlements over 2 000 p.e..
The percentage of the national population connected to urban waste water treatment facilities
In 2017, most countries collected and treated urban waste water from at least 80 % of their population. Some countries are building treatment facilities, with just 50-55 % of the population currently connected (Albania, Croatia and Romania). Between 60-70 % of the population are connected in Bosnia and Herzegovina, Ireland, Italy, Serbia and Slovakia, while in Bulgaria, Lithuania, Poland and Slovenia, between 71-76% of the population are connected to urban waste water treatment.
It is not certain what the gap between the top of the bar and 100 % population represents. It could represent missing data or that people are not connected to the public waste water treatment system.
It is not always appropriate to connect to the public waste water treatment system, for instance in remote areas with low population density. Suitable alternatives to connection to the public sewerage system can include package waste water treatment plants, drain fields and septic tanks with regular removal of solid waste, and robust monitoring and inspection (Ricardo, 2019).
2. The percentage of the national population connected to tertiary urban waste water treatment facilities
Waste water is treated to a tertiary level, for example to remove nitrogen and phosphorus, which otherwise can cause nutrient pollution. In EU-27 countries (EEA-2020), 68.9 % of the population were connected to tertiary treatment facilities.
Figure 2 shows that there was widespread, tertiary treatment already in place in a few countries by the 1990s (Finland, Germany, Sweden and Switzerland). In several older EU Member States, significant efforts to improve levels of treatment were undertaken during the 1990s and 2000s (Austria, Belgium, Denmark, Greece, the Netherlands, Portugal, Spain and the United Kingdom). In recent years, investment in the treatment of urban waste water, particularly in the newer EU Member States, has been directed at higher level treatment (Bulgaria, Czechia, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovenia). This may reflect that these countries have designated their entire territory (or most of it in the case of Slovenia) as 'Sensitive Areas', which leads to an obligation under the UWWT Directive to treat waste water more stringently in agglomerations over 10 000 p.e.
There are several countries where more than 40 % of the population were served by treatment below tertiary level in 2017 (Albania, Bosnia and Herzegovina, Ireland, Malta, Portugal, Serbia, Slovakia, Turkey and the United Kingdom). Some of these countries are islands, have long coastlines, have designated only fractions of their territory as Sensitive Areas, and/or are candidate countries and potential candidates of the EU.
Figure 2 shows the development of urban waste water treatment in countries since 1990.
In most cases, it is possible to see the building of collection facilities, increasing the proportion of the population connected, and the level of treatment provided becoming higher. The decline in collection without treatment, or primary treatment, is replaced by light and dark green bars, signifying secondary and tertiary treatment.
The adoption of the Urban Waste Water Treatment Directive in 1991 promoted the improvement of urban waste water treatment in the older EU Member States. As new Member States joined, they improved collection and treatment, often rather rapidly (e.g. Bulgaria, Croatia, Hungary, Poland). Implementation has been strongly supported by EU cohesion policy, with EUR 38.8 billion provided for the waste water sector since 2000 (EU Commission, 2019).
The European Commission is carrying out a Fitness check of the EU water legislation, and published an evaluation of the Urban Waste Water Treatment Directive and the Fitness Check of the Water Framework Directive in 2019.
Recent research into Covid-19 has shown the potential of monitoring non-infective traces of the virus in untreated waste water, to rapidly estimate the level of infection in a large population (WHO, 2020).
Figure 3 summarises the type of treatment applied in the urban waste water treatment plants of 'big cities' in 2016 (where 'big cities' are urban settlements of over 150 000 p.e.). Of the total generated load of larger cities, 86 % receives 'more stringent treatment', typically to remove nitrogen and/or phosphorus, but may include disinfection. 10 % of the total load receives secondary treatment, while 1 % of the total load of all 'big cities' receives only primary treatment and 0.5 % is neither collected nor treated.
The indicator on urban waste water treatment, WAT005, 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 from 'big cities' is expressed as population equivalents (p.e.).
The indicator illustrates:
The percentages of the population connected to primary, secondary and tertiary urban waste water treatment facilities (Figures 1 and 2).
The percentage of population equivalent (p.e.) was used for “big city” treatment (Figure 3).
The main objective of the Urban Waste Water Treatment Directive (91/271/EEC) (UWWTD), and equivalent national legislation for non-EU countries, is to protect surface waters from the adverse effects of waste water discharges. The UWWTD prescribes the level of treatment required before discharge to surface waters. It requires Member States to provide all urban settlements (called 'agglomerations' in the UWWTD) 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 urban settlements of more than 10 000 p.e., with various size classes. The performance of the treatment is assessed using several determinands (biochemical oxygen demand (BOD) and chemical oxygen demand (COD); plus total nitrogen and total phosphorus in the case of more stringent treatment).
For urban settlements 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 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 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 UWWTD. Based on the substances listed in Annex VIII WFD, the following are important for this indicator:
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.
Collecting and treating waste water has required huge investment across Europe in recent decades. The kinds of new challenges facing urban waste water treatment, such as climate change, resource efficiency and improved environmental protection, are set out in the EEA briefing Urban waste water treatment for 21st century challenges.
Further information on emissions from industry to water, including to urban waste water treatment plants, is available in Industrial waste water treatment - pressures on Europe's environment.
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 have complied 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 urban settlements 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 urban settlements 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 UWWTD should be seen as an integral part of achieving good status for all waters under the WFD.
The indicator is based on data from Eurostat, which show the percentage of the population connected to each treatment type. Compared with previous versions of the indicator, Figure 1 now shows the treatment level in EEA member and cooperating countries in 2017, rather than grouping countries according to region.
A p.e. of 1 is equivalent to an organic biodegradable load having a 5-day BOD of 60 g per day.
Tertiary treatment is known in the UWWT Directive as 'treatment more stringent than secondary' and includes the application of secondary treatment.
'Big cities' is a term used in the UWWT Directive for cities of at least 150 000 p.e. or agglomerations responsible for large waste water discharges. Countries themselves identify their 'big cities'.
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. 2016 data carried forward to 2017. This approach was used for up to 5 years of gap filling, i.e. 2012 data could be carried forward to up to 2017.
The main uncertainties relate to data reported to Eurostat. In 2005, treatment for 24 % of the population was 'unknown', which fell to 15 % in 2017. The second area of uncertainty relates to numbers of inhabitants, as these do not necessarily align with reported population data, though error here is generally small.
The 'EU-27' value is strongly influenced by the situation in Member States with large populations (France, Germany, Italy and Spain).
At country level, the population figure and the generated p.e. load are not usually the same, as there can be other sources of organic pollution, such as food industry and temporal changes in population owing e.g. to tourism.
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).
'Big cities' data sometimes include data from agglomerations that are much smaller than 150 000 p.e. However, the impact of such errors on the final percentages is rather small.
Data from the UWWT Directive focuses on the performance of the treatment plant and of the agglomeration. 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 the definitions of different classes of treatment (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.
For references, please go to https://eea.europa.eu./data-and-maps/indicators/urban-waste-water-treatment/urban-waste-water-treatment-assessment-5 or scan the QR code.
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