Turku Region wastewater treatment plant, photo by Robert Seger
In the unique model adopted by Turku, wastewater is treated efficiently while producing eco-friendly energy. The system is under continuous development. Turku prepares for challenges to wastewater chains posed by climate change.
The cargo ship Scot Pioneer has arrived at the Port of Turku. A crane carefully moves the enormous pipes, 2.5 metres in diameter and 21 tonnes in weight, from the hold to the wharf. A specially designed industrial truck transports the pipes to the storage area.
The CEO of Turun seudun puhdistamo Oy (Turku Region Wastewater Treatment Ltd) Mirva Levomäki explains that these pipes will soon make up the new removal channel of the Kakolanmäki wastewater treatment plant.
“Roughly 800 metres of outlet pipe will be jacked underground. Another 300 metres in the beginning of the pipe will require quarrying.”
Climate change means that rainfall will increase, downpours will become more frequent and the sea levels will rise
The new removal channel will help Turun seudun puhdistamo Oy prepare for climate change and the extreme weather phenomena it generates.
“Climate change means that rainfall will increase, downpours will become more frequent and the sea levels will rise. Currently, treated wastewater is drained to the sea along the city’s rainwater sewers, but during heavy rain, their capacity is not quite enough. Our new removal channel will eliminate this bottleneck.”
In connection with the removal channel construction, the treatment plant will also receive a UV disinfection unit. After the UV treatment, the wastewater treated at Kakolanmäki will meet the hygienic requirements set for bathing waters.
Load to sea areas has decreased
Located deep in the bedrock, the Kakolanmäki treatment plant centrally treats the wastewaters from 14 municipalities with a total of about 300,000 residents, as well as the region’s industrial wastewater.
The plant was implemented in 2009. Since then, the phosphorus load of municipal wastewater on the nearby sea areas has decreased by 80%, the organic matter load by 60% and nitrogen load by over 50%.
As is typical in Finland, the Kakolanmäki treatment plant is a traditional biological-chemical activated sludge plant. The phosphorus is removed chemically using ferrous sulphate, and the treatment is completed by sand filtration. The UV plant currently being built will be introduced in 2023.
“We will make extensive use of automation and online control. This allows us to react quickly to changing situations and needs, e.g. changes in water amounts and loads or possible wastewater emissions. Furthermore, in the event of high flow, the spillover water treatment unit is turned on.”
Overflow survey helps protect sensitive environments
In addition to the removal channel, another big development project of Turun seudun puhdistamo Oy is also linked to climate change.
We will make extensive use of automation and online control. This allows us to react quickly to changing situations and needs, e.g. changes in water amounts and loads or possible wastewater emissions.
The company commissioned a survey of the entire wastewater network covered by the treatment plant from Valonia, Southwest Finland’s regional advisory organisation in matters regarding sustainable development, in order to chart risks to sensitive environments posed by possible network overflows. In the area of the 14 municipalities that own the treatment company, the network consists of over 2,000 kilometres of wastewater pipes and around 500 pumping stations.
“By identifying risk areas, we can target municipal network renovations and plan better preparatory measures in order to reduce overflow. These measures can be especially targeted to sensitive and vulnerable sites, such as groundwater areas, valuable fishing waters, public beaches and nature conservation areas.”
Special attention paid to stormwater
Wastewater network overflow usually takes place in connection with downpours when the pipe capacity is not sufficient. Due to climate change, these extreme weather phenomena are likely to become increasingly common.
Levomäki explains that heavy downpours and resulting stormwaters weaken the efficiency of the Kakolanmäki treatment plant and cause additional costs, as the plant must treat rain and meltwater that ends up in the wastewater network in addition to normal wastewater.
“The automatic spillover water treatment unit doubles the plant capacity during rainy seasons,” she mentions.
Stormwater management is also taken into account in urban planning. Together with other Baltic cities, Turku has sought novel solutions that prepare for heavy downpours and stormwater issues. For example, green spaces absorb water and increase environmental comfort.
Clean water and eco-friendly energy
The Kakolanmäki wastewater treatment plant also includes pioneering energy solutions. Whereas treatment plants usually are the largest energy consumers in their area, the Kakolanmäki plant acts as an energy producer.
“In cooperation with Turku Energia and Turun Seudun Energiatuotanto Oy, the Kakolanmäki treatment plant uses heat pumps to produce district heating from the wastewater heat that would otherwise go to waste. District cooling is produced at the same time. The eco-friendly treatment plant complex produces over ten times more energy than it consumes.”
The heat pumps produce over a tenth of the Turku region’s district heat and reduce carbon dioxide emissions by about 80,000 tonnes each year.
The municipal wastewater sludge is also utilised according to the principles of circular economy. The cooperation partner Gasum Oy turns it into liquefied biogas for road traffic use. The process also generates soil conditioners and nitrogen nutrients for industrial purposes.
Text: Matti Välimäki
Images: Photo of Mirva Levomäki by Jere Anttila / Turun seudun puhdistamo Oy; other photos by Robert Seger