Prague wastewater treatment: Today and in the future Jiří Wanner

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1 Prague wastewater treatment: Today and in the future Jiří Wanner Department of Water Technology and Environmental Engineering, Institute of Chemical Technology, CZ , Technická 5, Prague 6 The history of the sanitation of Prague and the development in wastewater treatment until the 20 th century has been described by the author in article History of Prague sewer system and wastewater treatment (see Section Wastewater Treatment in Prague at Lindley directed all of the main trunk sewers to the location where the Vltava river leaves the town today, on the bank of the navigation channel. The channel and the main stream of the Vltava river create an island at that point, which is called Cisarsky (Emperor s island) because it used to be the private property of Emperor Rudolf II (1552 to 1612). At the beginning of the 20 th century the island was in Prague s suburbs, but Lindley foresaw the future growth of the city and so installed all of the wastewater processing technology in the building s basement. The building itself, which was built in the style of industrial secession (Art Nouveau), was used only for administration of the plant, laboratories, boiler room and engine room, and for storing chemicals. The map of the Emperor s Island: left) 19 th century; right) today Steam engines were used as sludge pumps and for the pumps that discharged effluent to the river during high water conditions. The wastewater treatment plant was formally commissioned in 1906 and construction of the complete Prague sewerage and wastewater treatment system was finished in The treatment process was based on screening, grit removal and sedimentation, in a battery of underground decanters. The whole complex is preserved to this day, including Lindley s original mechanical equipment. The plant was converted into a museum, which is open to the public ( 1

2 The orthophotomap of the Emperor s Island: left) 1950s; right) today Wastewater treatment from the 20 th century to today As Prague s population and industry grew, the capacity of Lindley s plant was eventually exceeded. In spite of several minor upgrades it became evident in the 1930s that Prague needed a new wastewater treatment plant. Several projects were begun, some of them with features similar to contemporary mechanical-biological wastewater treatment plants. However, World War II ended all activities in this field. The idea of a new biological treatment plant came to fruition in 1965, when a completely new wastewater treatment plant on Cisarsky island was commissioned, known as the Central wastewater treatment plant (CWWTP). This plant, designed under the technical supervision of Professor Maděra, was the largest activated sludge plant in central Europe at that time. However, it soon became obvious that even the new plant had its limits. The first problem was that the hydraulic capacity of the biological stage, especially the capacity of the secondary clarifiers, was less than the mechanical treatment capacity. The other drawback of the plant was the capacity of the aeration basins, which were designed in the early 1960s for biological oxygen demand (BOD) removal only, with no nitrification. There were a number of further developments in Prague s wastewater treatment. From 1973 to 1975, upgrades were undertaken to improve the hydraulic capacity of the biological stage to 4.5m 3 /sec by installing new secondary clarifiers. From 1982 to 1985 the first complete reconstruction and upgrade of the plant was undertaken, which increased the aeration capacity, amongst other things. From 1988 to 1991 preparatory works began for the displacement of the CWWTP, for instance by constructing a new siphon to take wastewater from the island to the northern bank of the river Vltava, a project that finally ended due to political changes in the country. The first stage of a plant upgrade took place between 1995 and 1997, taking the total capacity to 7m 3 /sec, and introducing nitrification in the activated sludge system by constructing four new secondary clarifiers, with a central flocculation zone and a regeneration zone. 2

3 Aerial view of the existing Central Wastewater Treatment Plant in Prague, located on Cisarsky island. 1) regeneration zone; 2) four new secondary clarifiers; 3) Lindley s underground plant. Credit: Sweco Hydroproject CZ. Between 1999 and 2000 short-term measures were taken, particularly the stabilization of the nitrification process by applying in situ bioaugmentation of the nitrification bacteria (Wanner et al 2009). Despite these measures the CWWTP was still not able to fully nitrify and denitrify its wastewater, and therefore did not achieve the requirements of EC directive 271 for total nitrogen limits. From 2002 to 2003 the CWWTP was being reconstructed after the great flood of August 2002, and in 2004 the City Council looked at the future of wastewater treatment in Prague. The main idea was to divide the treatment between two plants one part of the wastewater being treated in the existing CWWTP and the rest in the so-called New water line, which will be built on the free land available in the southern part of Cisarsky island. Administrative and technical preparations for the New water line were undertaken between 2005 and 2010, and the technical solution was presented and discussed at the 10 th IWA Specialized Conference of Design, Operation and Economics of Large Wastewater Treatment Plants in Vienna, 2007 (Wanner et al, 2009). In 2011, final preparations for the tender were made. An independent commission of experts on wastewater treatment, law and economics evaluated the received bids; a political decision was made in the City Council and the winner was declared (a consortium of Czech, French and German companies: SMP CZ, Hochtief CZ, Degrémont and WTE Wassertechnik). The contract between the city and the winning consortium was approved in July From September last year to January this year, preparation of the building permit documentation was undertaken, and since March work has been undertaken on administration and obtaining the permit this is due to complete in June. In July, construction work will 3

4 begin, with civil engineering works due to continue until The technology will then be installed, and through 2017 gradual preparations will be made for trial operations. On 15 December 2017 the plant will be handed over to the city and trial operations will begin. This first step will be followed by the complete reconstruction of the existing water line. The final stage of the Prague wastewater treatment solution will be characterised by the parallel operation of the New water line and the reconstructed old water line, with total wastewater inflows divided in the ratio of about 2:1. The reconstruction of the existing CWWTP water line will be followed by a complete reconstruction of the current sludge management facilities. This may be accompanied by a change in sludge stabilisation technology, which is currently thermophilic anaerobic digestion. Visualization of Cisarsky island after the New water line is complete (New water line in the right, the existing CWWTP in the left). Credit: City of Prague, City Investor Department. Visualization of Cisarsky island after the New water line is complete (New water line in the front, the existing CWWTP at the upper end of the island). Credit: City of Prague, City Investor Department. The current situation and future prospects The city of Prague announced the winner of the tender in September The project was supposed to be financed by the EU Environment operational programme, but financing negotiations with the Brussels authorities were not successful. The amount of money requested for the project was about CZK5.9 million ($302,800). The EU s executive arm did 4

5 not grant the subsidies because Prague had previously agreed a contract with the Veolia water management company for too long a period, which apparently breached fair competition rules (Kenety, 2012). Given this new situation, in 2012 the City Council established a new committee of experts who re-considered all of the technical and financial aspects of the winning project, with the aim of finding out whether there are alternative technologies that could be used and whether savings might be possible. The committee worked very intensively from April 2012 until January 2013, and with an 80% majority voted for the technical solution in the winning project, recommending some areas where savings would be possible. After complicated political negotiations in the Assembly of the city of Prague and in the City Council, in July 2013 the Council approved the New water line project for CZK5.8 million ($291,000). The project will be financed from the budget of the city of Prague. In November 2013 the city signed an amendment to the contract with the consortium for a final price of CZK 5.79 million ($290,000), with the construction period due to last until the end of This means that after 15 December 2017, treated Prague wastewater discharged to the Vltava river will meet the EU s effluent standards for large agglomerations in sensitive areas. At the same time, the architectural solution for the New water line will follow Lindley s original concept of an invisible wastewater treatment plant. The final step that will enable construction of the New water line to begin was taken by the City Council in December 2012, when it appointed Prague s water company (PVS) as the superintendent of construction (PVS is the city company that manages the city s water infrastructure). References Ecotechnical Museum Praha (2004), The History of the Prague Sewage System. Edited by Jan Palas. Jásek, J (2006), William Heerlein Lindley a Pražská kanalizace. Archiv hlavního městs Prahy. Documenta Pragensia Monographia, Prague. ISBN (In Czech) Kenety, B (2012), Prague fails to secure EU subsidies for wastewater treatment plant. CzechPosition.com, Wanner, J (1996), Vývoj stokování a čistírenských technologií. SOVAK, 5(7-8), (In Czech). Wanner, J (2000), Historie stokování a čištění odpandích vod v Praze. ENERGIE, 4, (In Czech). Wanner, J, Kos, M and Novák, L (2009), Intensification of Prague Central WWTP Ten years of Practical Experiences with the in-situ bioaugmentation nitrification method. Water Practice and Technology, 4(1), doi: /WPT Wanner, J (2014) Prague moves towards modern wastewater treatment. IWA Yearbook, pp