Abstract
Objectives
This study evaluated a pilot-scale system for recovering inorganic nutrients from recirculating aquaculture system (RAS) effluent using membrane-based water treatment. The primary goals were to 1) evaluate the system performance to produce an inroganic concentrate suitable as fertilizer, 2) investigate the storage stability of the concentrate in room temperature with and without heat treatment, and 3) perform plant cultivation trials using the concentrate to replace mineral fertilizer.
Method
The pilot system was installed at NIBIO Landvik, Norway. The system consisted of a research-scale salmon RAS, a water treatment unit, and a vertical hydroponic farm. Atlantic salmon (Salmo salar) were grown in 1000 liter tanks at a density of 70-100 kg/m3. Weekly, 900-1200 L RAS effluent was processed in 300 L batches. The resulting concentrate was collected, and analyzed for chemical and microbiological stability during 6 months of storage at room temperature. Hydroponic plant cultivation trials were performed to evaluate the suitability of the concentrate as a fertilizer.
Results
The system successfully produced a nitrate- and potassium-rich concentrate with low levels of phosphate. The hydroponic trials showed that the concentrate can replace a significant portion of mineral fertilizer use without compromising product yield. Storage trials showed that the concentrate remained chemically and microbially stable for at least 6 months storage at room temperature, independent of heat treatment.
Conclusion
Production of concentrated RAS effluent can alleviate our dependency on mineral fertilizer and reduce the environmental impact of salmon farming. To address nutrient imbalances, the concentrate can be combined with other organic inputs or other media to tailor a complete fertilizer. Further work will focus on system scalability and economics, and the potential for reusing clean water.
This research is part of the IPN Nutricycle project and funded by the Research Council of Norway (#336971).