3.2 Water quality

3.2.1        Main issues

Until the end of the 19th century, water quality in rivers and lakes was generally satisfactory in most parts of Europe. Gradual deterioration was experienced around 1900 with the industrial revolution, the concentration of inhabitants in cities and the development of industrial production. Great volumes of sewage and industrial wastewater were discharged into rivers and lakes from towns and the self-purifying processes of recipient water bodies were not sufficient to assimilate the pollution impacts. In the decades to come, the volumes of sewage drained into rivers and lakes without any treatment were rising as a result of the increasing percentage of inhabitants living in houses connected to sewerage. At the same time, industrial water pollution was also increasing as the construction of industrial plants was not accompanied by the construction of wastewater treatment plants.

By the 1970s, some European rivers such as the Thames in London were declared biologically dead due to the disposal of untreated effluents, industrial chemicals and low oxygen levels. Also in southern Europe, uncontrolled water pollution severely impacted the quality of urban rivers such as the Tiber in Rome and the Lambro in the Milan metropolitan area.

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River pollution in the metropolitan area of   Milan

The River   Lambro drains a very densely populated and heavily industrialized zone,   including a significant portion of the Milan metropolitan area with a   population of more than three million. Before the construction of a treatment   plant in 2002, almost all of the sewage from the city of Milan, as well as   industrial sewages flowed untreated into the river. The Lambro is considered   to be one of the most polluted rivers in Italy: its basin was declared at   high environmental risk area in 1987. Many fish species which used to live in   the river have, as a result, disappeared, including for example the bleak (Alburnus alburnas), the eel (Anguilla anguilla), and the European   perch (Perca fluviatilis). The   situation was even worse after an environmental disaster in 2010, when a huge   quantity of oil was criminally dumped into the river, causing unprecedented   damage to fauna in particular (Salvini, 2011).

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After periods of heavy rain, water quality degradation in urban rivers and lakes can also rise significantly due to overflows from the sewage network. In many European cities, the sewer systems are designed to receive both foul sewage and surface water following rainfall. These so-called combined sewer overflows (CSOs) are there to prevent overloading of sewers and wastewater treatment plants. After heavy rain a mixture of surface water and sewage can be discharged to the water environment via the CSOs. Discharges from CSOs may impact on water quality, including hygienic elements such as pathogens and viruses that influence bathing waters and in turn affect human health. For this reason, there are frequent public warnings to avoid bathing in urban rivers, lakes and coastal waters after heavy rain. There is need to properly protect CSOs by upstream measures (e.g. nature-based retention basins) and manage them to prevent flooding and minimise adverse impacts on the environment and public health.

Across  the  EU,  a  diverse  set  of  data  is  available  on  stormwater  overflows. Although several EU Member States have an advanced understanding on stormwater overflows, a comprehensive overview of overflows at Member State (or regional) level is still not available for a large number of countries (Cools et al,. 2016).

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Another persistent problem of concern to citizens is chemical pollution of river and lake sediments in cities. For instance, the constant need for dredging sediment in the River Elbe and the harbour of Hamburg to allow inland water transport has, next to concerns about the impact of the hydrological changes to the ecosystem, faced the city authorities with the problem of how to dispose of polluted sediments (Leal et al., 2006). Another example is sediment pollution of Lake Rummelsburg, an oxbow lake of the river Spree, in a densely populated area of Berlin. The high contamination of the lake sediments with chemicals due to industrial activity on the river banks in the early 20th century is made responsible for the low biological diversity of the lake. Nowadays, the area around the lake progressively develops to a residential area and is popular for local recreation use. Recent remediation measures by the city authorities, such as partial sludge removal, have not improved the ecological situation significantly so far (Dumm et al., 2015; Reifferscheid et al., 2013). The city of Stockholm is also taking measures to deal with sediment pollution in its lakes, e.g. of Lake Trekanten which is a popular recreational spot close to central Stockholm.

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Treatment of polluted sediments in Lake   Trekanten, Stockholm

Lake   Trekanten (Lake Triangle) is a small but important recreational lake (13,5   ha) located in a very densely populated area close to central Stockholm.   Although suffering from eutrophication and pollution with heavy metals and   hazardous substances, the lake is extensively used for swimming and fishing   by local residents. Fish restocking with rainbow trout is done regularly and   crayfishing is a popular activity. A large number of measures have been   implemented as a response to the water quality problems of the lake. Several   measures have been analytical in character, some have focused on monitoring   to support analyses, while some measures have been of remedial character such   as the aluminum treatment of sediments to bind phosphorous and the   implementation of a solution for the treatment of stormwater emanating from   the major highway.                                                                   

Photo: @   Juha Salonsaari, Stockholm Municipality

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3.2.2        Response of cities to water quality degradation

In 2011/2012, only 14 of the 28 capitals[1] of EU Member States could be considered to be in full compliance with the EU Urban Wastewater Treatment Directive (UWWTD): Vienna, Copenhagen, Tallin, Helsinki, Paris, Berlin, Athens, Budapest, Vilnius, Amsterdam, Lisbon, Madrid, Stockholm and London. A large number of European capitals are still not fully compliant with the requirements of the UWWTD: Brussels, Sofia, Nicosia, Prague, Dublin, Rome, Riga, Luxembourg, La Valetta, Bucharest, Bratislava and Ljubljana (European Commission, 2016).

Nevertheless, looking back to the past 25 years, clear progress has been made in reducing emissions into urban rivers and lakes due to connections to sewers, the introduction of wastewater treatment and the upgrading of earlier treatment plants. Implementation of the UWWTD, together with national legislation, has led to improvements in wastewater treatment across much of the European continent (EEA 2012a). For instance, Brussels’ River Zenne, has been notorious for being one of Belgium's most polluted rivers. All effluents from the Brussels Capital Region were discharged into the Zenne without treatment until 2007, when the completion of new sewage treatment plants began to remediate this problem (Zenne, n.d.).

In some cities of Eastern Europe, the recent construction and operation of wastewater treatment plants has achieved reduced emissions and water quality improvements, linked to the implementation of the UWWTD during and after their accession to the EU (see the example of Bucharest below).

In other parts of eastern and southern Europe, still much progress needs to be made. For instance, in Serbia only 16% of the population is connected to wastewater treatment plants and the largest cities, including Belgrade, Niš and Novi Sad release their wastewater untreated into the passing rivers (Vujovic´ & Kolakovic´, 2015), the Danube and the Nišava (Sava river).

  • voet (Jan Hendrik Voet) 30 Aug 2016 14:35:06

    Would it be possible to make 2 corrections on page 29 point 3.2.2) :

    « A large number of European capitals are still not fully compliant with the requirements of the UWWTD: Brussels, Sofia, Nicosia, Prague, Dublin, Rome, Riga, Luxembourg, La Valetta, Bucharest, Bratislava and Ljubljana (European Commission, 2016). »

    * Brussels is compliant since november 2014.


    « For instance, Brussels’ River Zenne, has been notorious for being one of Belgium's most polluted rivers. All effluents from the Brussels Capital Region were discharged into the Zenne without treatment until 2007 2000. In 2007, the the completion of a second new sewage treatment plants contributed greatly to remediate this problem (Zenne, n.d.). »

    Contact: Alice Thienpont


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Wastewater   treatment in Bucharest

Bucharest is situated   on the banks of the Dâmbovița River, which flows into the Argeș River, a   tributary of the Danube. Bucharest is supplied with water by three drinking   water plants, located outside the city perimeter. The Argeș river is the main   source of raw water for two of the drinking water plants, while the Dambovita   river supplies the third water plant.

Until 2011, Bucharest   discharged wastewater from more than 2 million inhabitants without treatment   into the river. These wastewaters (from both domestic and industrial use) had   seriously deteriorated both the Dâmbovita and Arges Rivers and made Bucharest   the largest polluter of the Danube in the region. The construction of a   wastewater treatment plant in Bucharest began in 1985 but was abandoned in   1996 because of lack of funds. By 2000, the need for an operational   wastewater treatment plant became increasingly obvious. Furthermore, Romania   declared its whole territory a sensitive area according to the Urban   Wastewater Treatment Directive, which requires all agglomerations of more   than 10,000 population equivalents to have wastewater treatment plants with   the highest degree of treatment, the removal of nitrogen and phosphorus.

In 2011, a wastewater   treatment plant, Glina WWTP, started to operate in Bucharest and it will be   further developed until 2017. After its completion, the plant will ensure the   treatment of the entire wastewater flow of the Bucharest urban area and will   discharge an effluent which will meet the requirements of national and   European legislation, thus eliminating one of the major pollution hotspots in   the Danube River basin (http://www.icpdr.org/main/publications/hotspot-no-more-wastewater-treatment-plant-bucharest).  

The operation of the   wastewater treatment plant can significantly reduce the impact of Bucharest’s   urban wastewater on surface water resources. Since the operation of the plant   started in 2011, the total pollution removal from the wastewater by the   treatment plant has steadily increasedfrom 242 t/day to 340 t/day (Apa Nova   Bucureşti S.A., see factsheet in Annex to this report). Since 2014, the total   pollution removal is even higher than the design level of the Glina WWTP.

According to the WFD   compliant monitoring results at the level of water bodies located on the   Dambovita River (downstream of the Glina WWTP discharge) and on the Arges   River (the last water body before discharging into the Danube River), the   concentrations of organic and nutrient pollution indicators have   significantly decreased in the last 5 years, leading to improvement of river water   quality. It should be highlighted that in the receiving Dambovita water   bodies, approximately 50 % reduction in the concentrations of organic   substances (COD and BOD) have been registered, while total nitrogen and total   phosphorous concentrations have decreased by approximately 30% and 60% respectively   (Source: National Administration ”Romanian Waters”).

The project has also contributed to increasing public’s awareness of the   pollution effects of wastewater and the responsibility to protect river   ecosystems.

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A special restoration tool used to combat eutrophication in lakes with high nutrient concentration is biomanipulation. It is often used as a means additional to efforts to reduce external nutrient loading via improved wastewater treatment or diversion of nutrient-rich inflows. A biomanipulation project has, for example, been implemented for the Lake Ülemiste, which is the main source of drinking water of Tallinn, Estonia.

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Biomanipulation in   Lake Ülemiste, Tallinn

A biomanipulation project was one of the main measures   taken to protect Tallinn’s drinking water reservoir (Lake Ülemiste) and   improve water quality. The aim of the project was to increase the abundance   and size of herbivorous zooplankton in order to control phytoplankton biomass   and therefore improve the water quality in the lake. Improved water quality   helps to reduce the chemical and energy costs of treatment caused by high   phytoplankton biomass in the water (Panksep et al. 2009; Panksep, 2009).

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Improvements in the water quality of urban rivers and lakes due to reduced emissions and wastewater improvement have brought about benefits to river and lake ecology. In many European capitals, the flagship species salmon has returned to their rivers. In Paris, the wild salmon returned to the Seine after an absence of nearly a century. Salmon is not the only fish in the Seine making a comeback. The number of fish species in the Seine has increased significantly since 1995 due to the improvement of water quality made possible by a new water purification plant (The Telegraph, 2009). In London, there has been significant improvement in water quality in the last 40 years and more than 100 species of fish have been found in the Thames Estuary in recent years, many of them within the city of London (McCarthy, 2010). Other examples include the return of the salmon to the once heavily polluted River Tolka in Dublin after an absence of 100 years as well as to the rivers of Oslo (see box below). In Sweden, it has been made possible to resume the recreational salmon fishery in downtown Stockholm, where salmon fishing had to be stopped in the 1960s as fish had become inedible due to heavy pollution.

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Return of the salmon to the rivers of   Oslo

Most   rivers and streams in the city of Oslo have had a long history of poor water   quality until the early 1980s. This was reflected in low benthic diversity   and the absence of fish. At the end of the 1970s, considerable efforts were   made to limit industrial discharges, pollution episodes, and urban runoff,   resulting in a substantial improvement in water quality. This improvement in   water quality resulted in major changes to the benthic fauna and fish   populations of the rivers, especially the River Akerselva, which runs through   the city centre. The Atlantic salmon, which became extinct in Oslo in the   mid-1800s, returned to the Akerselva in 1983. Atlantic salmon and sea trout   now spawn in the lower reaches of the River Akerselva, and the river supports   juvenile populations of these salmonids (Saltveit, 2013). 

Jumping salmon in the River   Akerselva, city of Oslo (Photo: @Dan P. Neegaard)

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Many cities across Europe have also been taking specific measures to reduce wastewater discharges from combined sewer overflows after heavy rainfall. In the city of Copenhagen, the improvement of water quality from similar measures has even enabled recreational bathing in its harbour.

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Copenhagen: From   sewer to harbour bath

In Copenhagen, Denmark, many years of investments in the   sewerage system have revitalised the harbour. For decades, the discharge of   wastewater from sewers and industrial companies had a major impact on the   water quality in the city harbour. The water was heavily polluted. In 1995,   93 overflow channels fed wastewater into the Copenhagen harbour and the   adjacent coastlines. Since then, the municipality has built rainwater   reservoirs and reservoir conduits, which can store wastewater until there is   space again in the sewage system. This has resulted in the closing of 55   overflow channels. Today, wastewater is only discharged into the harbour   during very heavy rainfall (http://www.dac.dk/en/dac-cities/sustainable-cities/all-cases/water/copenhagen-from-sewer-to-harbour-bath/).  

Municipal investments in modernising the sewerage system   and expanding the city's wastewater treatment plants have revitalised the   harbour of Copenhagen. In 2002, the first public harbour bath opened and   today there are four harbour baths. An established on-line warning system   calculates and monitors the water quality in the harbour (http://www.dhigroup.com/upload/publications/scribd/105175057-Copenhagen-Harbour-Bath-DHI-Case-Story-DK.pdf).   If the water quality is poor, the swimming facilities are immediately closed.

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In the city of Aarhus, Denmark, in order to reduce discharges from combined sewer overflows, new rainwater retention basins were created and an integrated real time control system set up to allow for coordinated operation of the sewer systems and wastewater treatment plants. These actions are part of a large urban restoration project, including uncovering the River Aarhus to reconnect it to the city landscape. Similarly, in the city of Lódz, Poland, measures to counteract stormwater overflows and quality degradation in the urban stream Sokołówka have been combined with a restoration programme for the river and its valley. In London, the Lee Tunnel has been constructed to capture and prevent 16 million tonnes of sewage mixed with rainwater from overflowing into the River Lee each year. The tunnel is the deepest ever constructed under London and forms a key part of the biggest expansion of London’s sewerage network since the 1860s (Thames Water, 2016).

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Aarhus - Rainwater management against   combined sewerage overflow events

The River   Aarhus serves as a natural structure connecting the centre of Aarhus,   Denmark’s second largest city, with the port. To respond to the severe   pollution of the river and to promote infrastructure development, the River   Aarhus was converted into a covered concrete channel in the 1930s. In 2010,   still about half of the water in the river consisted of treated wastewater   and around 55 combined sewage overflow (CSO) systems discharged into the   river (Basso, 2010).

The city   authorities have implemented a series of measures to uncover the river, with   the purpose to enhance the aesthetics of the city, to promote recreation, to   enhance climate adaptation and flood protection and to reduce the frequency   of sewage overflows during extreme rainfall events. These measures included   the establishment of two upstream lakes to reduce nitrogen and   phosphorus flows into the Bay of Aarhus, the construction of new rainwater   retention basins and the implementation of an integrated real time control   system to allow for coordinated operation of the sewer systems and wastewater   treatment plants.   Additionally, a water quality early warning system was installed in Lake   Brabrand, River Aarhus and the harbor (Stahl Olafsson et al. 2015). So far,   these measures have resulted in a significant change in the way citizens and   visitors experience the river, which now forms a blue corridor lined with new   waterfront amenities and the harbour where bathing has now become safe   (Hvilsoj & Klee, 2013; Aarhus Municipality, 2008).

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Łódź: Stormwater retention and ecological   quality improvement

The River   Sokołówka is a small, urban stream running through the northern part of the   city of Łódź, the third largest city in Poland. The catchment spans urban, as   well as agricultural and natural areas. In the early 1930s, the upper reaches   of the river were straightened, deepened and partially canalized. The main   channel of the urban stream was converted into a collector for 50 stormwater   outlets. These developments resulted in adverse effects on the urban and   surrounding ecosystems, and the Sokołówka and adjacent rivers were polluted   with discharge from combined sewage and stormwater overflows several times   per year.

Most of Łódź   rivers work as a part of a combined sewerage system of the city. During heavy   rains, rivers intercept waters from overflows and rain water. Shortage of   stormwater retention reservoirs is one of the reasons for pollution of the   biggest river of the city, the River Ner, which receives combined sewage from   the entire city.

The   repeating problems related to pollution, overflows and ecological degradation   made the city look for possibilities of stormwater retention, and for   improving the ecological quality of the rivers, thus creating friendlier and   healthier public space.

The city   of Łódź has implemented a comprehensive urban development programme on water   and river restoration, part of which has been the restoration of the River Sokołówka . For the River Sokołówka, a   sequential stormwater sedimentation-biofiltration system was implemented,   which prevents the influx of pollutants into the river during high flows   (Zalewski et al. 2012). Five retention reservoirs were constructed in order   to increase river retention and pollution absorption capacity. These measures   went hand in hand with development plans for a further rehabilitation of the   river valley (Wagner and Breil, 2013).

As a   result of the measures taken, the river and its valley have turned into an   attractive residential and recreational area which has contributed to the positive   economic development in the wider area (Wagner et al. 2007). The creation of   new green areas as part of the restoration activities has had positive   influence on the quality of the   inhabitants’ life and their health.The restoration of the Sokołówka River has been used as a   demonstration case to gather experience that can then be used for further   replication on other streams and rivers crossing the city. The demonstration   projects implemented by the city of Łódź have played an important role in   creating visibility, interest and cooperation, and as such have been vital in   the scaling-up strategy of the project.    

Zgierska   pond in the urban catchment of the Sokolowka River after restoration. (Photo:   ©Anita   Waack-Zając)

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