Tampere is the third largest city in Finland and the largest inland centre in the Nordic countries. Tampere is home to 225,150 inhabitants, and close to half a million people live in the Tampere Region, which comprises Tampere and its neighbouring municipalities. Tampere is one of the three most rapidly developing regions in Finland. It is a centre for leading-edge technology, research, education, culture, sports and business.
It is estimated that waterfall in Finland will increase by 25% in the coming years due to climate change. A critical issue for Tampere is therefore flooding and storm water management. As both demonstration areas in Tampere are under construction to become dense urban areas, the rapid population growth will pose a significant challenge. Other challenges that the city is facing include air and water pollution and reduced biodiversity.
Tampere’s main NBS demonstration site is Vuores. Vuores is a new greenfield district surrounded by natural waterbodies, which is in the construction phase. The first residents moved to Vuores in 2010 and there are currently 3000 inhabitants living in the district. Intensive construction is still ongoing, and it is planned that Vuores will be completed by 2030, with residences for 13,000 people and 3000 to 5000 jobs.
Vuores consists of existing and developing residential blocks located around multifunctional parks. Vuores stormwater management system is one of the largest in the Nordic countries and the northernmost of the world. The heart of the Vuores nature-based stormwater management system is the Central Park, where retention ponds, swales, wetlands, and streams retain and purify the water before leading them to lake Koipijärvi. The nature-based water management system starts already from plots, where e.g. green roofs, rain gardens, and rainwater harvesting serve both as water management as well as recreation.
One of the initial NBS demonstration ideas of the city included further development of the Vuores nature-based stormwater management system. A biofilter is the first part of the UNaLab demonstrations in Vuores and has been built in Park Virolainen to treat stormwaters from nearby residential blocks and streets. The biofilter is capable to decrease the nutrient and microbiological load in the water. A detailed plan for supplementary nature-based solutions, such as bioswale, alluvial meadow, and submerged dam, has also been prepared.
Innovative, co-created NBS systems demonstrated in Vuores will be scaled up and further developed in the brownfield area Hiedanranta, which is also situated in Tampere. Hiedanranta is a former industrial area slated for development into a dense city district for 25,000 inhabitants and more than 10,000 jobs. Currently, Hiedanranta is open for people to enjoy and organise cultural- and art events and other innovations.
The first UNaLab demonstration in Hiedanranta is a pilot-scale algae-based water treatment system where researchers from Tampere University of Technology study microalgae growth in Nordic conditions. A biofilter has also been installed in Hiedanranta to treat the contaminated water from an old pulp mill.
Online water monitoring devices have been installed to monitor NBS performance in the urban living labs and the results can be accessed online. Tampere is also planning on implementing a green roof on one of the buildings in Hiedanranta.
NBS Case Study
Biofilter in Hiedanranta
Saturday, December 15, 2018
Ramboll, City of Tampere, Carbofex Oy
One of UNaLab's demonstration areas in Tampere is Hiedanranta, which is a former pulp mill area 4 km from city centre. It is going to be developed into a dense urban area of 25 000 residents and 10 000 jobs. In the current urban planning phase, the City of Tampere has opened Hiedanranta to be an innovation platform where new ideas, pilots and urban culture flourish. Due to the area's industrial history, soil is contaminated and there is an old industrial landfill that contains mostly fibre waste.
To treat nutrient-rich seepage waters from the old landfill and to build a purification system that can be utilised in Finland and abroad. Neutralising the unpleasant odours caused by the water, binding carbon and increasing the number of pollinating insects.
In autumn 2018, a biofilter (area 100 m2) was built to purify nutrient-rich leachate. Water is conveyed into the biofiltering layers with an underdrain on about 1 m depth. The soil layer below the underdrain is around 400 mm deep peat-based growth medium that contains spruce biochar. In the drainage layer of the system, light gravel aggregates are used to improve pollutant and odour removal. The drainage layer also includes an underdrain pipeline that finally conveys treated water to nearby lake Näsijärvi. The topmost layer of the biofilter is a common growth layer enabling several plant species to grow. The species include flowering plants that offer a good living environment for pollinators. Activated charcoal is used for neutralising the unpleasant odours. The performance of the biofilter is monitored through two automatic stations and water samples.
Potential Impacts/ benefits:
Initial results show that the biofilter removes at least nitrogen, phosphorus and solids from the landfill leachate. At best, the nitrogen levels can be decreased by almost 80% and the phosphorus levels by 90%. The amount of solids can be decreased by 90% as well. The solution has also proven to work well in winter conditions. On the other hand, the large amount of meltwater has affected the biofilter’s performance when the filter capacity has been exceeded. The vegetation to be planted may improve the situation as the roots of the plants increase the absorption of water into the filter materials. Studies will be carried out concerning how the biofilter binds carbon and increases the number of pollinating insects.
Transferability of the result:
A well-designed and properly built biofilter with a suitable capacity can effectively remove solids and total nutrients. Biofiltration is also effective in removing bacteria and phosphates. It should be noted that the biofilter can only handle relatively small amounts of water and, in the case of overflow, nutrients and other contaminants may be leached out of the structure. The advantage of biofilters is that they can be built into a small space.
Biofilter can only handle relatively small amounts of water. With a large drainage basin and therefore large amounts of water, the capacity of the biofilter needs to be sufficient or, alternatively, multiple solutions need to be used.
Project manager Maarit Särkilahti email@example.com, Project planner Salla Leppänen firstname.lastname@example.org