University of Oulu

Pulkkinen, J. T., Ronkanen, A.-K., Pasanen, A., Kiani, S., Kiuru, T., Koskela, J., Lindholm-Lehto, P., Lindroos, A.-J., Muniruzzaman, M., Solismaa, L., Klöve, B., & Vielma, J. (2021). Start-up of a “zero-discharge” recirculating aquaculture system using woodchip denitrification, constructed wetland, and sand infiltration. Aquacultural Engineering, 93, 102161.

Start-up of a “zero-discharge” recirculating aquaculture system using woodchip denitrification, constructed wetland, and sand infiltration

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Author: Pulkkinen, Jani T.1; Ronkanen, Anna-Kaisa2; Pasanen, Antti3;
Organizations: 1Natural Resources Institute Finland, Survontie 9A, 40500 Jyväskylä, Finland
2Water, Energy and Environmental Engineering Research Unit, Faculty of Technology, 90014, University of Oulu, Finland
3Geological Survey of Finland, Neulaniementie 5, 70211 Kuopio, Finland
4Natural Resources Institute Finland, Latokartanonkaari 9, Helsinki, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4 MB)
Persistent link:
Language: English
Published: Elsevier, 2021
Publish Date: 2021-04-19


Recirculating aquaculture systems (RAS) discharge management limits the development of the aquaculture sector, because RAS do not automatically result in low nutrient emissions. Research has helped develop discharge management systems such as wetlands and woodchip bioreactors that have been adopted by Danish commercial model trout farms. To further develop the Danish concept, we have modelled and built a novel “zero-discharge” recirculating aquaculture system with an annual capacity of approximately 14 tonnes. The aim of this paper is to describe the entire concept and present the results from the start-up phase of the whole system. The concept includes the treatment of RAS effluent (overflow and sludge supernatant) using a hybrid solution of a woodchip bioreactor, constructed vertical wetland, and sand infiltration. Using this three-step process, the nitrate, phosphorus, and organic matter effluent are decreased to acceptable levels to reuse the water in the RAS process reducing the need for new raw water. In the first nine months of operation, a water treatment field was used as an end-of-pipe treatment to ensure the water was safe to recirculate for fish. During the winter, the water temperature dropped to 2.7 degrees in the sand filter, but the frost did not reach the water levels in any of the treatment processes. It therefore appears that a hybrid solution can operate sufficiently even in winter conditions. In the first year of operation, a woodchip bioreactor can remove 97 % of the nitrate, although the slow start-up of the RAS caused the bioreactor to be N-limited. On average, 79 % and 92 % of the inflow phosphate concentration was removed in the woodchip bioreactor and the entire hybrid treatment field respectively. The wetland and sand filter removed organic matter sufficiently (35 %), but because of the longer than designed actual water residence, it leached from the bioreactor more than was expected. Further experimentation is needed to identify the financial applicability and performance during higher feeding rates.

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Series: Aquacultural engineering
ISSN: 0144-8609
ISSN-E: 1873-5614
ISSN-L: 0144-8609
Volume: 93
Article number: 102161
DOI: 10.1016/j.aquaeng.2021.102161
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: This study was supported by the Finnish Ministry of Agriculture and Forestry, Natural Resources Institute Finland, and the European Union through the European maritime and fisheries fund.
Copyright information: © 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (