HSY’s two wastewater treatment plants, Viikinmäki in Helsinki and Suomenoja in Espoo, are responsible for the processing of wastewater in the Helsinki metropolitan area. We are building a new wastewater treatment plant in Blominmäki, Espoo, which will be completed in 2022. The Blominmäki wastewater treatment plant will replace the current Suomenoja wastewater treatment plant.
Mechanical, chemical, and biological methods are required for wastewater treatment. They are used to remove debris and most of the organic matter, nitrogen and phosphorus from the wastewater. Sludge and biogas are generated as by-products of wastewater treatment. The sludge is further processed into soil and the gas is utilised as a source of energy. The treated wastewater is led into the open sea in a tunnel.
In addition to wastewater generated in households’ everyday use, industrial wastewater and other non-domestic wastewater are also discharged into sewers. Discharging these into the sewer is subject to licence and requires an industrial wastewater contract.
Wastewater treatment is an important part of the protection of coastal waters and the Baltic Sea, as the wastewater to be treated is rich in phosphorus and nitrogen nutrients that would cause severe eutrophication if discharged directly into the sea.
Restrictions have been placed on wastewater treatment in both EU directives and national legislation. In addition, wastewater treatment plants are required to comply with the plant-specific environmental permits issued to them, the implementation of which is monitored by the Uusimaa ELY Centre.
Viikinmäki wastewater treatment plant
The Viikinmäki wastewater treatment plant located in Helsinki is the largest treatment plant in Finland and the Nordic countries. The wastewater of approximately 860,000 residents from not only Helsinki, but also the central and eastern parts of Vantaa, Kerava, Tuusula, Järvenpää, and Sipoo are processed at the Viikinmäki rock treatment plant.
Suomenoja wastewater treatment plant
The Suomenoja wastewater treatment plant, which started as a pond treatment plant in 1963, is the second largest wastewater treatment plant in Finland. The wastewater of approximately 390,000 residents from Espoo, Kauniainen, the western parts of Vantaa, Kirkkonummi, and Siuntio are processed at Suomenoja. The Blominmäki rock treatment plant will replace the Suomenoja plant in 2022.
Blominmäki wastewater treatment plant
We are building a new wastewater treatment plant in Espoo’s Blominmäki bedrock. The caves to be excavated underground will host the wastewater treatment basins and the majority of other plant facilities.