Recovering nutrients from aquaculture industry by-products for the production of bio-based fertilizers

The aquaculture industry generates large quantities of animal by-products that need to be managed appropriately to minimize their potential health risk (EC1069/2009). The fish sludge, composed of fish feces and animal feed, requires a special attention since the fast growth of land-based aquaculture during the last years and the ever-increasing application of recirculating aquaculture systems have significantly increased the volume of sludge generated. The composition of the fish sludge, with a high content of nutrients and minerals, evinces its potential as a fertilizer product. Nevertheless, its direct use as a natural fertilizer is limited by governmental regulations, being necessary to examine suitable processes based on a holistic approach to produce agronomic value products. To overcome this challenge, in the framework of SEA2LAND project, BETA Technological Center is evaluating an innovative valorization system integrating technologies such as membrane systems, freeze concentration, biodrying, thermal treatment coupled to phosphorous-ash recovery and acid scrubber, to obtain products with agronomic value to be applied directly as bio-based fertilizers in field crops and others to be used as precursors for the formulation of tailor-made fertilizers. The fertilizing products obtained are: i) a nutrient-rich concentrate, ii) ammonium salts, iii) a phosphorous-rich organic amendment and, iv) phosphoric acid.