Against the flow: water management transformation

Finland’s oldest city, Turku, might be renowned for its vibrant harbour, medieval castle and cathedral, but at its centre is a futuristic underground facility that deserves to be equally celebrated.

Looking for all the world like a small town, the city’s wastewater treatment plant occupies four kilometres of underground tunnels blasted out of the solid rock of a hill beneath existing buildings.

“Having a wastewater treatment plant in the middle of a city usually comes with unappealing smells and logistical problems,” explains Björn Grönholm, Director of Strategic Projects in Turku.

“Going underground means you can overcome these problems, using pipes rather than lorries for transport, while also creating more consistent operating conditions. People live above the plant and don’t even know it’s under their feet!”

This bold approach adopted by the city for the Kakolanmäki treatment plant extends far beyond its location and encompasses an array of innovative environmental, energy efficiency and circular economy solutions.

This same enlightened approach informed the design of the second major element of the city’s comprehensive new water system: the Virttaankangas drinking water plant, which was conceived as a balance of old and new ideas.

It’s clear why such an ambitious overhaul of its water management system was needed when you know the full scale of the issues facing Turku two decades ago.

Mud, algae and industry bring pressure for change

Shortage of groundwater is a global challenge waiting to be solved by just about every major city. Then there are the risks posed to water management by extreme weather conditions associated with climate change that result in too much or not enough water.

For Turku these challenges were just the start.

By the turn of this century, Turku already didn’t have enough groundwater to cover all consumption. And when there was more water around thanks to heavy rains, urban run-offs increased and ended up in the waters of the adjacent Baltic Sea, causing pollution from poisons such as phosphorus and nitrogen.

“We have one of the biggest archipelagos and the water here in our marine area is very shallow so there’s a lot of green and blue algae growth,” explains Grönholm. “We know this is connected to our river system so it was of the utmost importance to decrease nutrient pollution and have a positive effect on the water quality of the Baltic Sea.”

There was also increasing pressure to improve drinking water.

“Twenty years ago, the city was known for its poor quality water, which was muddy thanks in part to all the agricultural activity upstream,” says Grönholm. “This mattered not just for our citizens but also for our industry. We have a lot of biotechnology and pharmaceutical firms in the region for whom high quality water is vital.”

Our well-functioning and sustainable water services are the result of strong and visionary political leadership
— Björn Grönholm, Director of Strategic Projects for Turku

Impetus for change also came from the city’s ambitious climate change agenda. Aiming to be carbon neutral by 2029, when it turns 800, the city recognised that a new kind of sustainable, secure, climate-positive water management system would go a long way to help it achieve this goal.

Collaborating to save money and solve problems

The city was inspired to think big thanks to innovative agents in the city advocating for better water quality as a critical societal need and enthusiastic engineers championing the operational and environmental potential of novel management methods.

And once plans started taking shape, they got bigger.

“As the costs for the city’s plans became evident, we invited neighbouring municipalities to take action with us to reduce the expense and spread the risks for everyone,” says Grönholm. “This took strong political leadership to build trust and has been the making of the whole project.”

The result was the establishment of two new water companies owned by the city and between 9 and 14 municipalities, one responsible for drinking water, one for wastewater and both serving 300,000 inhabitants.

The city has continuously involved these residents in its grand water plan, helping them understand their role in achieving its objectives by reducing personal water consumption.

Working with universities, research institutes and companies, the city found the new solutions it was looking for to efficiently manage water, nutrients and energy through the entire water cycle.

The underground Kakolanmäki wastewater treatment plant is a model of sustainability
Drinking water is produced by converting river water into artificially infiltrated groundwater
The quality of Turku's drinking water is now recognised as among the best in the world

Holistic, hybrid plant design delivers

The resulting system takes advantage of both natural processes and the very latest technology – and is far more than the sum of its parts.

The drinking water supply solution, for instance, converts river water pre-treated using solar energy into artificially infiltrated groundwater which is naturally purified as it flows over 100km towards the city. As the water reaches the local underground reservoir, a turbine uses its gravitational flow to produce clean energy to power consumers’ water pressure. These nature-inspired methods are controlled and protected in a highly automated way with cyber security systems and 3D modelling tools.

The wastewater treatment plant, meanwhile, doesn’t just use a combination of biological, mechanical and chemical treatment processes to achieve purification levels far higher than regulations require. It also showcases the circular economy in impressive, innovative action.

Its heat pumping station enables 14,000 homes to be heated by wastewater through the district heating network, saving around 80,000 tons of CO2 emissions every year. A biogas plant, meanwhile, turns sludge into electricity, heat, transport oil and nutrients for fertilisers.

“The treatment plant produces about 10 times more energy than it uses,” says Mirva Levomäki, CEO of Turku Region Wastewater Treatment Ltd. “In addition, the carbon footprint of the plant complex is negative, which is better than carbon neutral. The main thing however is that the wastewater is treated to a very high standard, which promotes the wellbeing of the Baltic Sea.”

Top of the world and set for the future

In the 10 years since the plant’s launch, the Baltic Sea has seen its phosphorous load decrease by 83%, nitrogen by 60% and solids by 94%. In fact, the water flowing out to sea is now even drinkable according to one city official, with phosphorous levels so low.

As for Turku’s actual drinking water, Unesco awarded it joint top spot in an international quality evaluation. It also highlighted how the city’s integration of conventional and unconventional management methods paves the way for global adoption of plants like Virttaankangas to achieve the UN Sustainable Development Goals for water.

The wastewater treatment plant produces 10 times more energy than it uses, with the excess used to heat 14,000 homes
— Mirva Levomäki, CEO of Turku Region Wastewater Treatment Ltd

The city is now set to fair for the future, with a water system that can respond to greater demand as the city develops and is built to last for more than a century.

There’s just one thing the city has to be mindful of now: retaining the skills that enabled this project.

“The people who invented our water system are starting to retire and their knowledge and expertise are really important to the city,” concludes Grönholm. “We need to pass these on to the next generation and also inspire interest in the sector, which doesn’t have the most exciting image, so we can maintain our high level of innovation.”


Cities dream, act and lead our future. This example from Turku is one of the finalists for the Eurocities Awards, in the category ‘Lead together – scalable solutions for positive climate impact’. The winners will be announced on 9 June 2022 during the Eurocities Conference.

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