The amount of wastewater started to increase in the Helsinki Metropolitan Area in the late 1870s, when the Water Services Department started its operations and the construction of municipal sewer network was started. Already then, wastewater treatment was considered, but it was finally deemed unnecessary.
Water closets were introduced extensively in the beginning of 20th century, and this ruined the coastal waters around the cape of Helsinki, as most of the wastewaters were conducted directly from to sewers to the nearest coastal water area. Finally, the algae growth in Töölönlahti, complaints from the residents and the researchers’ worrying results about the condition of sea water encouraged the Health Committee to find suitable treatment methods.
The Treatment plant programme was launched
The first treatment plant was built in Alppila in 1910 and the next a few years later in Savila. These biological treatment plants were based on a septic tank method.
The treatment plants eased the situation of the badly polluted Töölönlahti somewhat, but the pollution load continued to grow in other coastal areas. Various solutions were suggested for the situation, but the negotiations took nearly two decades, until it was decided that instead of an open sea pipe, several more treatment plants would be built.
In the 1930s, two new plants that utilised activated sludge method were built in Helsinki: Kyläsaari and Rajasaari treatment plants. The construction programme of wastewater treatment plants was interrupted by the Second World War and the ensuing material shortage, and it could only be continued in the 1950s. During the next decade, treatment plants were built around the city up until the year 1970, when the nearly 40-year construction programme was finally completed as the Vuosaari water treatment plant was finished.
The growing city sets challenges
Although the wastewater treatment capacity grew rapidly in the 1960s, the population grew even faster at times. The city's sewer system also affected the treatment efficiency. So-called separate sewer systems were built into new city suburbs. The old sewer network of the inner city, on the other hand, was a mixed sewer, where rain water and wastewaters travelled through the same sewers.
Pollution spread further despite the new treatment plants. A wastewater committee established by the city suggested that the treatment process could be made more efficient by removing plant nutrients causing eutrophication of water areas from the wastewaters in addition to pathogens. Removal of phosphorus was first tried in the mid-1970s, and later on, this same chemical parallel precipitating method was introduced more extensively. Removal of nitrogen was not tested until the 1990s, but as the EU directives became stricter, these methods were also introduced later at the Viikinmäki treatment plant.
Merging and open sea pipe
The wastewater committee’s reintroduced suggestion about an open sea pipe gained popularity, but the project was not implemented until the 1980s, after another major project carried out by the water services, the Päijänne pipe, was completed. Municipal co-operation had been started already in the 1960s, and also Vantaa as well as a few other municipalities in central Uusimaa were included in this tunnel project. In Espoo, wastewater services had been launched in the beginning of the 1960s, when the decision about the construction of Suomenoja central wastewater treatment plant was made. It was decided that the treated water would be conducted to the open sea instead of coastal waters.
In the mid-1980s, only five of the treatment plants in Helsinki remained in operation. Already before the treatment plant programme was completed, the system had proved to be insufficient to prevent the pollution of nearby water areas. The City of Helsinki’s water and sewer department started to plan replacing the small plants with one large central treatment plant, like in Espoo. The decision to build a central treatment plant to Viikinmäki was made in 1986, and this major project was completed in 1994. The old treatment plants were demolished, but their equipment continued their operations on the other side of Gulf of Finland, in Estonia and Russia.
The sludge generated during the treatment process had been used as field fertiliser. In the late 1980s, worries about sludge’s too high content of heavy metals and radioactivity prevented its use as a fertiliser. When stricter norms for fertiliser sludge were planned, the City of Helsinki’s water and sewer department decided that all wastewater sludge would be composted to be used for green construction.
The City of Helsinki’s water services and sewer departments merged in 1984. In the beginning of 2010, the cities' own water service companies became history, as the new municipal federation started its operations.
The constantly changing cities and increasing amount of wastewaters will continue to set challenges in the future. Wastewater service should also be able to face the changes caused by climate change. In addition to local problems, water service issues are becoming more widespread, crossing both municipal and national borders and requiring more cooperation.
Herranen, Timo: Vettä ja elämää. Helsingin vesihuollon historia 1876-2001.
Laakkonen, Laurila, Kansanen and Schulman (Edit.): Näkökulmia Helsingin ympäristöhistoriaan. Kaupungin ja ympäristön muutos 1800- ja 1900-luvuilla.