Forthcoming fish farming in the Baltic region must be based on sustainable production technologies.

EU Directives

The Marine Strategy Framework Directive requires EU Member States to achieve 'Good Environmental Status' for their marine waters by 2020. Likewise, the Water Framework Directive sets limits to the nutrient discharge to areas already loaded with nutrients, such as the Baltic Sea. 

Thus, national aquaculture strategies must ensure that aquaculture does not have negative impacts in terms of non-indigenous species and eutrophication and there will be an increased the pressure for implementing aquaculture technologies with low nutrient discharges. It is therefore decisive, that forthcoming fish farming in the Baltic region is based on sustainable production technologies.

Recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are characterized by limitied water exchange and the use of biofiltration for reducing nutrient discharges. Hence, recirculating aquaculture systems provide technology for sustainable fish production in nutrient-sensitive areas such as Baltic Sea.

Furthermore, recirculating aquaculture systems virtually eliminates the risk of escapees and diseases spreading to the environment.

End-of-pipe treatment

Organic matter, phosphorous, and nitrate are the main end-products present in effluents from recirculating aquaculture systems.Treatment technologies for each “waste-product” are well-known from wastewater-treatment, however too expensive and laborious for aquaculture application. Furthermore, no information exists on their applicability in brackish or sea water.

In recirculating aquaculture systems, nutrients are mainly converted and subsequently removed from the farming system through particle separation (e.g. mechanical filters) and water replacement. 

Current technology for recirculating aquaculture systems uses much less make-up water than classical aquaculture systems allowing nutrients to accumulate within the system. From the concentrated effluent these nutrients can potentially be removed or retrieved in subsequent processes, termed end-of-pipe treatment. To sustain nutrient-balanced aquaculture in the Baltic area, efficient end-of-pipe technology and procedures are therefore needed.


The application of recirculating aquaculture systems is already increasing throughout the Nordic region. Alongside the maturation of recirculating aquaculture system technology and an increasing commercialization of this method of farming, focus is slowly shifting from mechanical/engineering issues towards more integrated and complex issues such as water quality and end-of-pipe treatment.

The prospective of being able to construct not only a farming system but actually a complete unit that can handle intake and especially discharge water and sludge is gaining more and more attention as system size and commercialization increases. 

Although recirculation technology has now reached a fully commercial scale, practical solutions to the removal or retrieval of nutrients in the recirculating aquaculture system discharge are still missing, in particular for brackish and salt water farming. Cost-efficient solutions are needed for further development of the industry and BONUS CLEANAQ will search for such innovative solutions.



17 JANUARY 2022