Jätevedenpuhdistus pääkaupunkiseudulla 2021

Wastewater in the Helsinki Metropolitan Area is treated at two of Finland’s largest wastewater treatment plants: Viikinmäki in Helsinki and Suomenoja in Espoo. The operation of the wastewater treatment plants is the responsibility of Helsinki Region Environmental Services HSY.

The operation of the wastewater treatment plants is governed by plant-specific environmental permits. In 2021, both of HSY’s treatment plants complied with all the environmental permit regulations: The biological and chemical oxygen consumption and total phosphorus content, as well as the removal efficiency of total nitrogen for treated wastewater, all met the permit regulations. The emissions to the sea were 1,067 tonnes for nitrogen (1,134 tonnes in 2020) and 26 tonnes for phosphorus (29 tonnes in 2020).

HSY’s wastewater treatment development projects in 2021 focused on phosphorus recovery, reducing greenhouse gas emissions, industrial wastewater and pharmaceutical management and the energy balance of heat recovery. New operating models were created to improve occupational safety, and work on updating the contingency plan was launched. A new maintenance system was taken in use. The work to reduce leakage water also advanced and a new combined sewers model was introduced.

In 2021, the Viikinmäki wastewater treatment plant produced 35 GWh of electricity. Viikinmäki’s electricity self-sufficiency rate was 92%. The Suomenoja wastewater treatment plant produced 4.5 million m³ of biogas. Gasum Ltd refines the entire amount of gas into transport fuel.

In the autumn of 2022, about two years later than originally planned, the new Blominmäki wastewater treatment plant, designed for the wastewater of approximately 500,000 residents, will replace the Suomenoja wastewater treatment plant, which has exceeded its design load. At the end of 2021, the overall completion rate of the construction site rose to approximately 91%. The highest completion rate is that of building technology works at approximately 97%, and the lowest completion rate, approximately 77%, is in electrical, automation and instrumentation works. According to the treatment plant’s current commissioning plan, redirection of the sewerage area’s wastewater to Blominmäki will begin by the end of August 2022, preceded by the transport of seed sludge to the digestion tanks and the active sludge process from the Suomenoja and Viikinmäki treatment plants. Training of operating personnel for the use of Blominmäki’s equipment started in autumn 2021.

The Viikinmäki wastewater treatment plant has been actively developed: increasing the capacity of secondary sedimentation systems is being studied by changing the flow arrangements of the basin. Funding from the Ministry of the Environment was received for energy efficiency renovations aimed at the digestion tank’s heat exchanger and aeration tanks. Both projects will continue in 2022.

COVID-19 has changed the ways of working in wastewater treatment in order to minimise contact. This has prevented local infection bursts. The number of blocked pumps has stabilised at around five times higher than before the pandemic. Wet wipes, face masks and protective gloves have been removed from blocked pumps. This has put a strain on the maintenance staff at the pumping station sites and shifted resources from preventive to corrective maintenance.

Keywords: Wastewater treatment, wastewater treatment plant, nutrient emissions, environmental permit, community nutrient load