In Summer 2025, AQUAPHOENIX partners in Åland completed the first phase of tests on novel sludge collection technology. They focussed on the first step of the process: pumping the waste (sludge) that accumulates beneath open pen fish farms.
During the pilot, technology manufacturers at Framo LiftUp collaborated with local fish farmers at Brändö Lax, with support from Åland Fiskodlarförening (Aland Fisheries Association) and LUKE (Natural Resources Institute Finland). They installed custom-made cages and pumps at Brändö Lax fish farms, and tested sludge pumping on a weekly basis.
Testing the pump was necessary to determine the amount of sludge that can be collected and the regional factors that may affect this, as well as for familiarising all parties with Åland’s specific conditions and tailoring solutions to local needs.
Åland experiences particular regional conditions, including relatively shallow waters, strong water currents, and low levels of salinity. Over the summer, partners investigated the optimal conditions for sludge pumping in this area. They found that sludge was more easily pumped on calm days, while stormy days brought strong winds and currents that tended to wash sludge away before it could be captured. When the full sludge collection technology system is installed in 2026, partners will plan to pump more regularly with the intention of capturing more sludge, even on days with strong winds.
The pilot also allowed scientists involved in the AQUAPHOENIX project to carry out some early tests. Fish sludge samples were collected and analysed for various water quality parameters. Flow velocity data were also recorded at the pilot site, using an automatic current meter. In Winter 2025, these datasets will be evaluated to assess how local water flow conditions influence the sludge collection system and to examine the contents of the fish sludge for nutrients such as nitrogen and phosphorus. These examinations will provide the basis for evaluating the potential of fish sludge as a circular resource, for instance by recycling it into a plant fertiliser.
Winter 2025 will also see partners planning for the full implementation of sludge collection technology in Summer 2026. This will entail installing pumps and dewatering systems on barges that will be attached to the fish pen, where sludge will be stored and transported to shore. Partners also plan to investigate how recovered sludge can be recycled for local uses.
In later phases of the project, the full installation of sludge collection technology in Åland sites will mark an important step in the transition to circular aquaculture and in support of a sustainable blue economy that the AQUAPHOENIX project is working towards.
