Filtralite removes half of the load of phosphorus and solid materials at Finland's third largest wastewater treatment plant.

The wastewater treatment plant built into the rock of Kakolanmäki, operated by Turun seudun puhdistamo Oy and owned by 14 municipalities, is quite a large plant even in regard to its treatment volumes. 

When it was put into operation on January 1, 2009, it replaced five old water treatment plants and currently cleans the wastewaters of close to 300,000 inhabitants of the Turku region, as well as the industries of the area. The length of the sewer network is over 2,000 km in the entire operating area with five hundred pump stations. 90,000 m³ of wastewater is treated daily at a high energy efficiency: the plant's energy output is ten times higher than its consumption, due to a heat pumping station.

Modern power plant 

The quadruple line treatment plant at Kakolanmäki is based on the mechanical, chemical and biological handling of wastewater. The cleaning efficiency concerning the removal of organic matter, phosphorus and solids is 99%, as well as over 80% for the removal of nitrogen.

Solid material is mechanically removed from the wastewater through screens and sand separation. Some of the solid material in the wastewater is also removed by pre-settlement. An aeration process then removes organic matter and nitrogen with the use of microbes, with the wastewater treatment chain completed by filtering the water through a layer of sand and Filtralite.

Cleaned wastewater is discharged into the Turku Linnanaukko harbour basin. The refined and dried sludge is in turn processed at Gasum Oy's biogas plant. The heat pumping station extracts some of the thermal energy from the wastewater to produce heat for district heating purposes. The water that is cooled down by the pumping station is also used for district cooling.

Functional granular polishing filtration

The wastewater treatment is finalized in a total of twenty sand filtration tanks at Kakolanmäki Wastewater Treatment Plant. – The filtration layer of each pool has half a meter of quartz sand, below a meter of Filtralite Clean MC 2,5-4 filter material, says process engineer Jouko Tuomi from Turun seudun puhdistamo Oy.

All in all, there is a total of 1000 cubic meters of Filtralite Clean MC 2,5-4 filter material manufactured by the Leca plant in Raelingen, Norway.

Jouko Tuomi says that the porous Filtralite has worked very well already for ten years. - Our polishing filters remove half of the amount of phosphorus and solids. The solids deposited onto the filters are removed by two-step counter-current rinsing once a day. The rinsing efficiently removes the filtered material from both layers. -

There has been no need yet to replace the Filtralite layer, Jouko Tuomi points out.

Kakolanmäki Wastewater Treatment Plant
Client: Turun seudun puhdistamo Oy
Contractor: YIT Rakennus Oy
Planning: FCG Planeko Oy 

Text: Dakota Lavento
Photos: Markku Pajunen