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Nature & Environment
The Spree River usually has a relatively high water quality as it approaches Berlin. In spite of some pollution from agriculture and mining, the water is generally good enough to swim in – even without filtering the water beforehand.
The decisive contamination of the Spree takes place only as it reaches Berlin; both the main Spree River and the Spree Canal are periodically polluted by overflows from Berlin’s combined wastewater system – with serious consequences for the water quality and ecological balance of the river. Roughly fifteen to twenty-five times per year, the rainwater that flows into the combined wastewater system exceeds the capacity of the pipes, so that their contents overflow untreated into the river – together with wastewater from Berlin households, which includes faecal matter, rinsing residues and hygienic products. The Spree then becomes so polluted that direct contact with the water can lead to grave health-related consequences for humans. In extreme cases, this process can also cause the death of large numbers of fish. After such episodes, it takes several days for the river to recover from the massive influx of wastewater. These heavily polluting discharges can be cleaned effectively by a plant filter – like the one which is part of the Flussbad project – so that people will be able to swim and bathe in the filtered water without any danger to their health.
The underlying principle of slow-sand filtration that forms the basis of the Flussbad project’s plant filter is a traditional and proven form of water filtration currently being used successfully all over the world, for example, in water catchment plants along rivers and streams (bank filtration) and in the construction of natural swimming pools. What is new, however, is the idea of filtering an entire canal in this manner. The filter is made up of a large amount of gravel particles interspersed with vegetation. In the process of moving through this filter, the water is naturally cleansed of impurities by microorganisms living in the spaces between the gravel particles. The vegetation – usually in the form of reed plants – generates an oxygen supply for the microorganisms and ensures the continuous movement of the filter’s contents, so as to prevent it from getting clogged up by silt. The Flussbad filter must be able to cope with input water of varying quality yet still always generate water that fulfils bathing-quality standards. Thanks to a study carried out the Flussbad project was already able to demonstrate that its filter was up to the task. In order to test these theoretical insights in actual practice – and also to be able to test the effectiveness of different filter configurations – we have built a test filter system into a 100 year-old barge belonging to the Brandenburgische Schifffahrtsgesellschaft e.V. (Brandenburg Shipping Society). This 1:80 reproduction of the Flussbad’s filter and swimming area will allow experts to monitor and evaluate the water quality over the course of two years. Details of the filter can be found on a separate board close to the ship.
In addition to filtering the water, the Flussbad project also seeks to prevent any future channelling of untreated wastewater into the Spree Canal. In the Kupfergraben area, this can be seen as a preliminary measure within Berlin’s overall efforts regarding the subject of combined wastewater; in other words, it is a measure that the State of Berlin will have to undertake anyway at some point in the near future. Another component of the Flussbad project is the idea of communicating the link between environment-related investments in the modernisation of wastewater infrastructure and the resulting increases in the quality of life and the environment in the city. The project wants to make it possible for people to comprehend and experience this link in a tangible manner as up-close and personal as possible.
The Flussbad project will preserve the Spree Canal’s current function in the overall Spree River system as a river arm with a continuous water flow. The project also seeks to improve the general water quality in the area near Museum Island. According to the guidelines contained in the European Water Framework Directive (EWFD), Berlin is obliged to undertake measures to improve the ecological quality of the Spree in the coming years. The Flussbad project would contribute to the implementation of these guidelines, most specifically with regard to the underwater topography near the Fischerinsel. In fact, the section of water between Inselbrücke and Gertraudenbrücke will be transformed into an ecological regeneration zone for flora and fauna. These measures are designed to convert this part of the Spree River – which is canalised over several kilometres as it makes its way through Berlin – into an “ecological stepping stone”.