Thorough wastewater purification is an essential part of the protection of the coastal waters and the Baltic Sea.
The inhabitants and businesses of the Helsinki Metropolitan Area produce approximately 130 million cubic metres of wastewater every year. Unpurified wastewater contains a great amount of phosphorus and nitrogen nutrients that would cause strong eutrophication if released into the Baltic Sea. This is why the purification process of wastewater must be efficient and reliable.
The wastewaters of the Helsinki Metropolitan Area homes and industry and the storm waters from the centre of Helsinki are lead through the sewer network either to HSY Viikinmäki or Suomenoja wastewater treatment plants. The purification process consists of mechanical, chemical and biological stages.
Due to the developed purification process, harmful nutrients such as nitrogen and phosphorus can be removed from the wastewater more efficiently than dictated in environmental licence regulations. This means that Helsinki is fulfilling the objectives of its Baltic Sea strategy by aiming for the best possible purification result. After purification, the wastewater is led to the open sea, eight kilometres away from the coast, in underground tunnels. Due to efficient and concentrated wastewater purification, the water quality in coastal areas and water bodies has significantly improved during the most recent decades.