Tommi Fred and Jukka Yli-Kuivila from HSY lead the way in Blominmäki WWTP's excavated caves, more than 20 meters below the sea level.

Tommi Fred and Jukka Yli-Kuivila from HSY lead the way in Blominmäki WWTP's excavated caves, more than 20 meters below the sea level.

26 Oct 2020

Wastewater treatment is key to protecting our Baltic Sea

Issued this October, NIB’s Blue Bond is financing a loan to the Blominmäki wastewater treatment plant in the City of Espoo, Finland. Once ready, the advanced treatment will significantly reduce the discharge of nitrogen and phosphorous into the Baltic Sea. Wastewater treatment is one of the fastest ways we can improve the state of our sea. Here is how it is being done.

From afar, only a 98 meter tall pipe, a landmark of sorts, gives away the exact location of the Blominmäki underground wastewater treatment plant (WWTP), even though it is one of the biggest and most expensive construction projects being carried out in the Helsinki metropolitan area.

In the Finnish October wind outside the cave, one needs a heavy wool coat and a scarf to stay warm. Inside, however, a mere cardigan and the neon yellow vest everyone on construction sites has to wear is enough. Once winter arrives, it becomes clear why it is wise to build wastewater treatment plants underground in the Nordics!

Tommi Fred, the Head of Service of Water Supply Management at HSY, Helsinki Region Environmental Services Authority, the owner of the project, explains the bedrock is exceptionally hard and solid in the Nordics, which is ideal for building underground WWTPs and makes it worthwhile.

“Building a wastewater treatment plant underground is clever use of land and it disturbs significantly less the surrounding environment. Thanks to this, we have been able to preserve the nature reserves and important wildlife corridors around Blominmäki,” Tommy Fred says.

Another benefit of underground WWTPs is that the energy economy of these plants is significantly better than the ones built above ground. For instance, the Blominmäki WWTP is expected to become entirely self-sufficient in terms of energy. This self-sufficiency will be achieved by digesting organic matter into biofuels that generate heat and electricity for the plant.

NIB started co-financing the Blominmäki underground wastewater treatment plant with a 30-year loan in 2015, the same year the construction of the plant began. Once operational in 2022, the Blominmäki plant looks to become the most productive of its kind in the Nordics. The new treatment plant will replace a wastewater facility in Suomenoja that has been operating for nearly 60 years and is reaching the end of its technical life.

Blue bonds for water ecosystems

More than 20 metres below the sea level, in the excavated caves of Espoo’s Blominmäki bedrock, wastewater from 400,000 inhabitants in the Helsinki metropolitan area will be treated carefully in a cutting-edge wastewater treatment plant that will directly help to protect the Baltic Sea.

“The protection of the Baltic Sea is at the very heart of HSY’s function. We exist to provide people with clean and fresh water that they can drink and use, but we also dedicate ourselves to rigorously cleaning the used water and that way, care for the wellbeing of the Baltic Sea,” says Tommy Fred.

The Baltic Sea is one of the most polluted seas in the world and suffers from eutrophication. This is fuelled by the high levels of nitrogen and phosphorus being discharged into it that result in excessive plant and algae growth.

The new Blominmäki wastewater treatment plant will treat wastewater significantly more thoroughly than the old Suomenoja plant, removing over 96% of phosphorus and organic matter and over 90% of nitrogen from the water. This will reduce the discharge of nitrogen loads into the coastal areas of the Baltic Sea by more than 300 tonnes per year.

On 6 October, NIB issued a new Nordic–Baltic Blue Bond focusing on water-related investments. The five-year SEK 1.5 billion bond was launched under the NIB Environmental Bond Framework and dedicated to finance projects within water management and protection, one such project being the Blominmäki wastewater treatment plant.

“This blue bond shows NIB’s continued commitment to protecting our water resources – it is only through constant, firm action that we can restore the much-needed health of our water ecosystems,” says Luca De Lorenzo, Head of Sustainability and Mandate at NIB.

Rock-solid WWTP

Disc filters spin through the wastewater, squeezing the water through the tiny holes in the discs, in the last phase of the tertiary treatment process. Just before, the water has been treated with UV light to remove microbes. These last phases of the wastewater treatment process are the ones that make the difference, cleaning the water more carefully than at the old Suomenoja plant or HSY’s WWTP in Viikinmäki.

The cleaned water will then flow to the open sea through a 16 kilometre long rock tunnel. The heat from the freshly cleaned water will be harvested for use in Espoo’s district heating and, only after this, will the cold and cleaned water be released to the Baltic Sea.

The Blominmäki WWTP is a complex construction project that demonstrates the craftsmanship of some of the biggest Finnish construction companies as well as the top know-how of more than hundred global subcontractors that have been cooperating on this massive construction project.

Jukka Yli-Kuivila, the Project Director of the Blominmäki project from HSY, explains how they have used very elaborate 3D building information modelling of the project.

“The precise modelling provides a useful tool for the future maintenance as well as refurbishment and upgrades that will keep the facility running efficiently,” says Yli-Kuivila.

The Blominmäki project has received recognition for its innovative and challenging construction design and modelling. In 2020, the WWTP project was awarded Best Industrial Project price by Tekla BIM Awards.

The excavations were completed in the winter 2018-2019, and now a cave complex of around ten hectares spreads below the Blominmäki area. In the future, the plant workers will be provided with bikes so that they have the opportunity to cycle around the web of tunnels that connect the different functional areas of the underground plant. A carefully excavated deepening is already waiting for the bike park. In summer 2021, once the construction work is completed, the plant workers will start to bike their way through the cave complex.

Our protein-heavy diets feed eutrophication

We should all be conscious of the fact that what we eat has a direct impact on the Baltic Sea. A trend that has been noticed at WWTPs is that, year after year, the waters passing through them contain more and more nitrogen. This is directly related to us consuming more protein than we actually need. Our bodies turn the excess protein into nitrogen and, through our toilets, it ends up at WWTPs and, ultimately, into our sea.

While we can trust the modern WWTPs to clean our waters efficiently, we all have our own part to play in protecting the Baltic Sea. Therefore, we should all critically think about our diets and consumption habits.

After all, we are the ones making the waste.