The first technical work that removed undesired water from one of Prague's buildings was a sewer, which drained the Premonstratensian Monastery at Strahov. When building the monastery in the mid-12th century, potable water was conducted from Petřín water galleries and at the same time, a drainage gallery that rid the complex of wastewater was built. At that time, the construction was unique and it was not imitated in the lower-situated town for many years.
Mediaeval Prague, just like other central European towns, was flooded by solid as well as liquid pollutants. Wastewater from cowsheds, cesspits and various basins overflowed to the streets and manure and rubbish piled up everywhere. The only road-cleaning came from heavy rains rather than a continuous effort of the town administration. In 1310, a sewer, which drained the provost's house in today's Nerudova Street, was built. However, we do not know where the waste was conducted. Another exception was a building from the second half of the 17th century. For drainage of Clementinum, the Jesuits built a large stone sewer in 1673, which conducted the sewage diluted with water from the college fountains directly to the Vltava River, and several other smaller objects.
One of the important modernizing projects involved initiation of construction of an underground Prague sewer in 1787 according to Leonard Herget's project. Financial problems, however, postponed the start of intensive construction until 1791. The progress was sluggish until 1816, because the house owners were obliged to pay a part of the costs for sewers that ran along their properties. It was the chief burgrave Karl, Count Chotek, who vigorously arranged termination of the first Prague public sewer system. Forty-four kilometres of sewers were built between 1816 and 1828. The sewers were terminated with thirty-five outlets directly in the Vltava River. As regards the technical and health aspects, the sewers had many flaws from today's perspective (a flat bottom, common bricks, clay instead of mortar, unsuitable diameters and insufficient gradients). They were cleaned by knackers, but gradually, a licensed sewer cleaning trade was established. The sewers were cleaned at night and the extracted material was transported to Nusle, Vršovice and Záběhlice for composting.
During the second half of the 19th century, the character of Prague, which was transforming into a modern metropolis, gradually changed. This transformation called for a change of its urban, communication and sanitary circumstances. The development of industrial manufacture resulted in an increase of the population and a great load on the environment. Engineering, chemical industry and production of building materials threatened the environment of the Prague basin more and more. The condition of the existing Prague sewer system also worsened because of frequent floods. Water from the flooded Vltava together with faeces penetrated to the Prague streets and also eroded the structure of the sewers from the inside.
In 1865, the Building and Economical Office was established and the sewer system was administered by its technical and economical department. Construction of a new sewer system in the capital of the Kingdom of Bohemia was inevitable. The "sewer issue" was introduced, which meant initiation of a discussion on the drainage method, or, if you like, removal of sewage from the Prague agglomeration. It was not only a technical issue, but also a political one, or rather a combination of both.
Thus, a Committee for Sewer Issues was established with the main goal of designing removal of sewage from the Prague agglomeration.
On 16th July 1884, representatives of the royal capital city of Prague opened a tender for a project involving the Prague sewer system. The project was to result in a unified system for all parts of the town with potential later connection to the surrounding suburbs.
Within the specified period by 1st March 1885, five projects were received; they were called "Kaumann", "Frisch gewagt" (With appetite, half is finished), "Sine munditia nulla sanitas" (There is no health without cleanliness), "Divissione" (By division) and "Praga caput regni" (Prague, the head of the kingdom).
The "Kaumann" project submitted by Ing. Kaumann from Wrocław incorporated, in addition to Prague, Vyšehrad and the suburbs of Bubny, Holešovice, Vinohrady, Žižkov, Smíchov and Karlín and planned construction of a wastewater treatment plant on Císařský ostrov.
The "Frisch gewagt" project drained only individual parts of Prague, mainly on the right bank of the Vltava and did not involve wastewater treatment.
The "Sine munditia nulla sanitas" project planned removal of sewage from Prague with Vinohrady, Žižkov, Karlín and Smíchov. The description of the sewage treatment is not quite clear in the project. It is possible that the author of the project calculated with two versions of treatment. According to the first version, all water collected in collection tanks was to be pumped into settling tanks about ten kilometres away from the town and mechanically treated there. The location of the settling tanks and the sewage transport route are not clear. According to the second version, the collected water was perhaps to be mechanically and chemically treated immediately in the collecting tanks and, after sedimentation, released directly to the Vltava River.
The project submitted as the "Divisione" by the Viennese company Rella und Neffe included two revolutionary elements. Firstly, it proposed a system of two separate sewer networks, which separately conducted sewage to the wastewater treatment plant and rainwater directly to the Vltava River. Secondly, he planned prolongation of the main sewage collector from the Old Town through an inverted siphon under the Vltava, then under Letná to Bubeneč, where he potentially considered construction of a wastewater treatment plant on Císařský ostrov.
The project marked "Praga caput regni" by Ing. Jan Kaftan proposed a unified "flushing" system for the territory of Prague with Vyšehrad. A wastewater treatment plant with sedimentation tanks and chemical treatment for sewage that was released to the Vltava was to be built in Holešovice.
The submitted projects were evaluated by a six-member committee between 23rd March and 23rd July 1885. After a detailed study of the projects, the committee reached the conclusion that none of the submitted projects completely fulfilled the specified conditions and recommended the city council not to award the first prize to any proposal.
Following this failed tender, a special sewerage sub-commission was established. Under the chairmanship of Franz, Prince of Thun and Hohenstein, in 1886 the sub-commission compiled a new "Programme for creation of a detailed project on treatment and removal of sewage in the royal capital city of Prague and its implementation" and its justification. In January 1889, the Prague municipality invited a number of important European experts for collaboration on the sewerage project, for example Dr. J. F. Hobrecht from Berlin, Ing. W. H. Lindley from Frankfurt am Main, Ing. Kaumann from Wrocław, Ing. Hallenstein from Munich and Ing. Kaftan from Prague. Of the renowned experts, only Dr. Hobrecht, Ing. Kaftan and Ing. Kaumann showed interest in creation of a new project. During the ensuing talks, Dr. Hobrecht recommended that instead of three recommended projects, only one joint project should be created by himself and Ing. Kaftan, as an expert in the local conditions. The city council unanimously accepted this proposal in October 1889 and secured it contractually.
The project that emerged was presented at the Jubilee Exhibition on the Prague exhibition grounds in 1891. The project involved removal of sewage from the area of 1,651 hectares. Sewers in the right-bank part of the town conducted wastewater to the lower edge of Karlín and to an inverted siphon under the Vltava River to Holešovice. The main sewage collector from the left side of the Vltava from the Little Quarter under Letná ran there too. The joint main sewer, to which the main sewage collector from Holešovice-Buben was conducted, was to empty into the Vltava below the bottom edge of Holešovice. This project did not incorporate wastewater treatment.
The conduct of the city council during placing of the project aroused great outrage. The local engineers Josef Václavek and Čeněk Ryvola were also dissatisfied. In a protest against their superlatives' conduct, they created their own project without a claim to pay and donated it demonstratively to the Prague municipality. Their project proposed division of the sewerage territory into two zones of various heights. The upper zone included the historical towns of Prague extending along both sides of the river and towns and neighbourhoods located above them. The backbone of the upper zone was a sewer terminated in an inverted siphon under the Vltava River between the Old Town and the Letná bank and a tunnel under Letná running to Bubeneč. The lower zone included the Petrská quarter, Karlín and Holešovice. The sewage collector ran to the Karlín inverted siphon and then along the Holešovice bank of the Vltava River. The sewer was to be terminated under Holešovice directly in the Vltava or continue through Královská obora to a planned wastewater treatment plant in Bubeneč.
As it was not politically acceptable to reject the "self-appointed" project completely, both proposals were evaluated and compared. The Prague council decided to invite a foreign expert who was involved in none of the projects. A building commissioner of Frankfurt am Main, the English engineer William Heerlein Lindley was chosen. First of all, he thoroughly acquainted himself with configuration of the Prague terrain and the geological conditions. He also carefully researched the suitability of the Letná massif for boring of the sewer tunnel. Then, he compared both projects in detail and the professional public anticipated that the city council would order revision of Václavek and Ryvola's project according to Lindley's comments. However, something different happened. William H. Lindley offered creation of his own project on Prague's new sewerage system and wastewater treatment plant and the city council accepted it. By this, the city council again overlooked local experts and, with a small trick, William H. Lindley reached the leading position in solving the Prague sewerage question.
In June 1893, Lindley handed the project with all details to the town. There was a very important chapter involving "meeting of downpours with high waters". One of the supplements included a graphic illustration of floods on the Vltava River according to the Old Town water level gauge between 1845 and 1892, which suggested that floods higher than two metres above the normal level were rare from April to September. The important conclusion was that "... higher floods do not meet with the heaviest downpours...". Consequently, the design of the sewer system had to ensure that when the level on the Old Town water gauge was two metres above normal level, it had to conduct the amount of rainwater to the Vltava River by rainwater outlets as soon as possible. This condition could not be fully satisfied only in Karlín and Holešovice.
The outfall of the whole sewer network was situated at Císařský ostrov in Bubeneč. At this point, Lindley acknowledged Václavek and Ryvola's project, which proposed a sewer tunnel under Letná as the shortest connection from the city centre to the Bubeneč wastewater treatment plant. The whole drainage was divided into system A and B. The larger A system covered parts of the town that could be connected by the Letná tunnel with the wastewater treatment plant in the shortest and most convenient route. The B system was drained by a sewer running through Karlín and Holešovice, also to the Bubeneč treatment plant. The project also involved separation of the flood zone. Immediately behind the direct flood line, the flooded district could be closed, while drainage of the non-flooded parts of the town was preserved. The shape of the sewer was ovoid with an elliptical arch because it best resisted the soil pressure. W. H. Lindley also specified brick as a material for construction of the Prague sewers. However, he had to overcome pressure from concrete companies, which referred to the concrete structure of the Viennese sewer system from 1878 as well as favourable prices of Portland cement in Prague.
The project also includes detailed parameters of the mechanical wastewater treatment plant, which had to manage 160,000 m3 of sewage per day. Lindley employed his experience with a wastewater treatment plant, which he had built in Frankfurt and creatively developed it in the Prague plant. He also calculated with transport of the sludge for agriculture, especially along lower reaches of the Vltava River.
The water-law approval process of the whole project was terminated with a positive verdict from the Imperial-Royal Vicegerency on 19th November 1894. Two months later, preparatory works for construction of the sewerage system and wastewater treatment plant commenced. Construction of the modern Prague sewerage system officially started with construction of the Old Town sewage collector at the start of 1898, although some of the works had started before. The other main sewage collectors were gradually under construction. In October, the sewer tunnel under Letná was dug. At this point, W. H. Lindley designed and drew a collection of Prague sewer anomalies, which, in fact are still used today.
In 1900, a detailed project of the wastewater treatment plant was finished. In 1901, Ing. Emanuel Heinemann officially took the position of a deputy to W. H. Lindley, the chief officer of the sewer office. In September 1901, the Quido Bělský building company started a difficult construction of the wastewater treatment plant by excavations for the sediment tanks. On 27th June 1906, a trial operation of a station with mechanical wastewater treatment began. On this day, a sluice gate on the A interceptor was opened and the sewage started to flow to the treatment process. Except for small defects on the pumps, everything worked perfectly and, less than half a year later, normal operation of all equipment was reached.
The year 1909 was the last year of W. H. Lindley's work in Prague. He gradually handed all documents from construction of the sewer system to his deputy and future successor Emanuel Heinemann, a building commissioner and Knight of the Austrian Imperial Order of Franz Joseph. After fulfilling all tasks that ensued from the contract and the subsequent amendments, W. H. Lindley said goodbye to Prague at a meeting of the supervisory board for the sewer system on 10th March 1909.
The activity of William Heerlein Lindley in Prague at the turn of the 19th and 20th century left behind a lasting trace not only to the history of Prague, but also the history of European technical thinking. The complexity of the Prague "sewerage issue" was exceptional and Lindley's concept became an example of the author's exceptional professional character. With its elaboration and significance, the project exceeded the Austrian-Hungarian border. Most of the constructed linear constructions still work for the Prague citizens and Lindley's wastewater treatment plant served for more than sixty years. This awe-inspiring work, together with the later-added modern water supply system, meant that the Capital City of Prague became one of the best hygienically provided for towns in Europe at the start of the last century.
The creation of Greater Prague in 1920 called for building of new sewers. As connection of the new territories meant a serious intervention with Lindley's concept, it was necessary to create new principles of Prague's drainage. In 1921, Ing. Máslo responded to emergence of Greater Prague by submitting a general project in 1925. It was based on re-calculation of the existing sewer network, especially with focus on the capacity of the Old Town inverted siphon in connection with the anticipated increase of wastewater from the new territories. He proved in his conclusions that the capacity of the existing sewer network would allow execution of the anticipated increase of the wastewater. According to his re-calculation, the Bubeneč wastewater treatment plant's capacity was insufficient, so he proposed construction of two new plants at the Botič - Vltava confluence and in Řež. In the ensuing discussion, the first plant was substituted with a proposal for construction of an inverted siphon under the Vltava River for transfer of wastewater to the Smíchov sewage collectors. The proposal for construction of the second wastewater treatment plant in Řež was accepted, but not implemented.
On 2nd May 1933, the Prague municipal council opened a tender for a general project on wastewater treatment plants in Prague. In total, fifteen projects were gradually inspected and rejected. In the meantime, from 1927, the first modernization of the Bubeneč wastewater treatment plant was executed. It sought to increase the treatment process capacity. A new water screen plant with two-part mechanical DORR screens was constructed and a new three-section sand trap and another four sedimentation tanks were built. In 1928, the field track that ensured transfer of materials was prolonged. The sludge had already been transported for one year on a special steamboat. This steamboat was produced by the Škoda Works and later, the Praga shipyard delivered another boat.
It was also necessary to inspect the sludge from all aspects and search for new solutions and utilization according to the analyses. For this purpose, Ing. V. Maděra established a special "Laboratory for research into the sewage and sludge and their impacts on the river" in the wastewater treatment plant, which became the first workplace of this type in this country. The laboratory conducted extensive semi-operational experiments with sewage digestion, while the produced biogas was used for heating of service water for the staff.
From the late 19th century until the early 1920s, the sewer system was built and administered by the Sewer Office of the Capital City of Prague. Following 1922, the Building Office of the Capital City of Prague, Department 9, took charge and, in the late 1920s, Department 9a separated and administered only operation of the wastewater treatment plant. This type of the Prague sewer administration was terminated in 1948.
Prompted by housing development in the early 1950s, the number of people connected to the sewer system sharply increased. It was necessary to gradually extend the sewer networks with new sewage collectors and common sewers to gradually drain areas connected to the capital city where the new-era housing development was in process.
Production of sewage rose to such an extent that Lindley's wastewater treatment plant was unable to process such an amount and part of the non-treated wastewater was released directly into the Vltava River even after another modernization in 1947.
After 1954, it was decided to build a new Central Wastewater Treatment Plant of the Capital City of Prague (ÚČOV) on Císařský ostrov. The appointed general designer was Hydroprojekt Brno. The project calculated with mechanical as well as biological treatment. An inverted siphon under the Vltava River for connection of the right bank was built between 1955 and 1957. At the same time, the direction of the watercourse was modified and the bottom was deepened. Subsequently, a new 11.5 km discharge pipeline for transport of digested sludge to Drasty was built and sludge beds were established. Construction of the wastewater treatment objects started in 1959. The new ÚČOV was ceremoniously opened in July 1966, while Lindley's plant ended its activity after sixty years of operation. However, the feed of the sewage had to be shut immediately after the end of the ceremony because of non-functional mechanical pre-treatment. There was no choice but to build a new water screen plant and modify the sand traps. It was not until 1967 that the mechanical as well as biological treatment was put into operation.
Even as the new wastewater treatment plant was put into operation, the capacity of the biological stage was insufficient for the needs of the capital. A part of the sewage was thus treated only mechanically. This situation was to be improved in the 1970s by a temporary intensification of the ÚČOV, but especially by construction of a new wastewater treatment plant in Hostín near Mělník. The work connected with higher efficiency of the treatment process proceeded between 1974 and 1985, but construction of the new water treatment plant was continuously postponed.
When the City of Prague overtook responsibility for the water supply and sewerage systems on its territory from the state, the Prague municipal council decided on another, i.e. the second intensification of the existing ÚČOV. The first stage proceeded from November 1994 until August 1997 and involved construction of four new sedimentation tanks, a new deep regeneration tank for biological sludge and other important improvements. However, as the subsequent stage, which was to increase capacity of the sludge management, was not implemented, the plant got into trouble with processing of the increased amount of sludge. The operator, Pražská kanalizace a vodní toky, thus solved intensification of the sludge management by installation of thickening and draining centrifuges, mixing the sludge with gas, mixing in manipulating sludge tanks and other investments. Thanks to these measures and other subsequent investments, it was possible to keep operation of the ÚČOV within acceptable operating parameters. However, it was apparent that the rising demands for treatment of the Prague wastewater could only be satisfied by a new wastewater treatment capacity.
Between 1999 and 2002 it became clear that for the property right aspects, it would be very difficult to negotiate location of the new plant outside the Capital City of Prague. Consequently, a feasibility study for reconstruction of the existing ÚČOV on Císařský ostrov was evaluated in five versions on a technical and economical level.
In 2000, a team of Czech and foreign experts compiled a theoretically feasible concept of the wastewater treatment plant. The first compilation included 26 options. The decisive aspect in the final selection was satisfaction of a demand to use only the area of the existing ÚČOV, even at the expense of higher investment costs, because utilization of the neighbouring area, the so-called garden plots, was not in agreement with the valid territorial plan.
At that time, talks were held on a change of the current territorial plan, which had up to then decreed that until 2010, the wastewater treatment plant was to be located outside the Capital City of Prague without determination of the location. The concept was based on division of the water treatment capacity between the existing ÚČOV and the new NČOV (New Wastewater Treatment Plant). The basic element of the intensification was increasing working volumes of the ÚČOV to satisfy demands for treatment processes of the water line in conformity with legislative demands, including rainwater treatment. Sludge management was considered jointly for the existing ÚČOV and the new NČOV. With small deviations, these concepts basically involved construction on Císařský ostrov in several stages, while keeping at least a partial operation of the existing ÚČOV with an alternative location and technology for processing of raw or digested sludge. However, this concept from 2000 was superceded by the Czech Republic joining the EU and an ensuing change of legislative demands, because it did not propose a treatment level according to parameters valid in sensitive areas.
Operation of the ÚČOV was destructively affected by the August flood of 2002. Dikes for the one-hundred-year water were not sufficient and the raging element caused damage to the water treatment equipment exceeding 300 million crowns. The mechanical treatment was restored at the end of October and the biological treatment started by the end of 2002.
Paradoxically, the August 2002 flood contributed to solution of the current as well as future needs for wastewater treatment in the Capital City of Prague. On Císařský ostrov, in the immediate vicinity of the current ÚČOV compound, a space, which opened after the flood, allowed wastewater treatment in combination of reconstruction of the existing plant and construction of a new water line. Following approval of this concept by the Prague authorities in November 2004, the technical solution was processed into the form of the project "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov".
The project involves construction of a new mechanical-biological wastewater treatment line with chemical coagulation and modification of the existing plant, focused on satisfaction of emission limits pursuant to Government Decree No. 61/2003 Coll. and Directive 91/271/EEC for sensitive areas, simultaneously increasing the plant's capacity by 183,560 population equivalents to the total capacity of 1,611,000 p.e. (i.e. 8.2 m³/s of mechanical-biological wastewater treatment) and further mechanical-biological wastewater treatment in the maximum amount of 3 m³/s during rainwater flows. Its implementation assumes total removal of 35,000 tons of pollutants per year according to the BSK5 indicator, undissolved substances 66,000 t/year, total nitrogen 7,000 t/year and total phosphorus 1,000 t/year. Implementation of the project respects the limited investment resources and optimisation of operating costs in relation to architectonic aspects of the whole ÚČOV compound and the landscape character of Císařský ostrov, the necessary level of flood protection, nature protection and minimising of potential negative effects of the operation on the surrounding area. The project is the largest water management project in the Czech Republic and one of the decisive infrastructural buildings of the Capital City of Prague. The anticipated benefits of its implementation are equally important. For example, regarding the total nitrogen indicator, the removed contamination will represent almost 30 % of the overall obligation of the Czech Republic to apply demands of Directive 91/271/EEC on urban wastewater treatment by the year 2010.
In 2005, an affirmative opinion of the Prague City Council Environment Office was issued on evaluation of impacts of this project on the environment (EIA) and the Prague municipal representatives approved a change of the territorial plan, because the project is to be partly implemented outside the contemporary ÚČOV compound. The investor's position in the "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov" from 1st November 2005 in conformity with decision of the Prague City Council of 19th July 2005, is secured by the City Investor Department of the Prague Municipal Council.
It was assumed that the project would be implemented between 2007-2010 with the cost estimate of ca. 9 billion crowns. For the Prague budget, sole financing of the "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov" represents such a load that utilisation of other financial sources is practically a condition for the implementation. With regard to the exceptional financial demands of the project, shared financing from the investor's own resources (the Capital City of Prague) and the European funds was considered from the beginning. With a view to a more favourable chance of drawing money from the Cohesion Fund for the financial period of 2007-2013, a request for shared financing of the "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov" was updated through an Operational Programme Environment (OPŽP).
A major obstacle in utilization of this programme, purposefully established for support of implementation of Directive 91/271/EEC on urban wastewater treatment, is the fact that in 2007, Conditions for Acceptability of Water Management Projects for OPŽP in the programme period of 2007-2013 were stipulated between the CR and the European Commission, stating that financing from the EU funds is impossible for projects in which validity of the contracts between the owner and the operator is longer than the end of 2022. A contract on sublease concluded with the operator (Pražské vodovody a kanalizace a.s) with the validity until 2028 practically eliminates Prague from having the chance to obtain financial support from this source.
Despite submission of an obligation of the Capital City of Prague to participate in funding of the "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov" in December 2011, the Control Commission of the Operational Programme Environment decided on 15th March 2012 not to administer the application any longer, thus not to send it for evaluation to the European Commission organs.
Thus, at present, organs of the Capital City of Prague are searching for an optimal solution to satisfy demands for the standard of wastewater treatment and procedures for its implementation in cooperation with leading water management and economic experts.
Approval of the concept for wastewater treatment in 2004 simultaneously decided on utilisation of the existing ÚČOV Praha objects. Therefore, implementation of certain measures that secure reduction of negative impacts of the ÚČOV Praha on the environment, the population and the surroundings (smell and noise) as well as proper operation of the ÚČOV (reconstruction of digestion and secondary settling tanks) proceeds simultaneously with preparation of the "Overall reconstruction and extension of ÚČOV Praha on Císařský ostrov" in conformity with evaluation of the project from the EIA perspective. Preparation and implementation of these investment measures for ÚČOV Praha is ensured by Pražská vodohospodářská společnost a.s. within its competences as administrator of water management property on the territory of Prague in a narrow collaboration with the operator.
In 2011, about 1.24 million Prague citizens were connected to the public sewer system and the length of the sewer system including sewer connections was more than 4,500 km. In the same year, the ÚČOV treated 119.6 million m3 of wastewater, the twenty subsidiary plants treated 9.8 million m3 of wastewater.
Text: Jaroslav Jásek, Jana Almerová, Photos: Archive of Pražské vodovody a kanalizace, a.s.