Several by products such as dead fishes, transformation remains, animals unfit for consumption, and fish sludge are generated by the aquaculture industry. In the framework of the SEA2LAND project, sludge produced from marine and freshwater aquaculture systems is being valorized by a portfolio of technologies to recover nutrients. Moreover, dead fish is being valorized as a co-substrate during the treatment of the solid fraction from freshwater aquaculture sludge. The marine aquaculture sludge is collected from a recirculating system for the production of the Sole specie, whereas sludge produced in the wastewater treatment plant from Trout processing is used in the case of the freshwater system. The solid fraction of freshwater sludge contains around 7.0 TKN, 0.4 TP, and 0.1 K on a dry basis For marine sludge, TP is the nutrient found in the highest content in the solid fraction 7.2 whereas TKN and K account for 3.8 and 0.2 on a dry basis, respectively. Regarding the liquid fraction, marine aquaculture sludge presents higher concentrations of TKN, TP, and K (1.74 0.43 and 0.37 in g/L, respectively) than freshwater sludge 0.33 g N/L, 0.02 g TP/L, and 0.02 g K/L). The use of trout as a co-substrate is also interesting because this by product presents high organic matter content, as well as valuable nutrients that could be recovered such as N 4.4 TKN) and P 0.4 TP) on a dry basis.

The physicochemical characterization shows that aquaculture by products contain nutrients to be recovered for the production of bio based fertilizers (BBF). The potential application of these BBF could reduce the costs associated with sludge management, bringing a new market opportunity for the aquaculture sector.

Fig 1: Aquaculture by products characteristics
Fig 2: Aquaculture by products (A: dead fish; and B: sludge from marine aquaculture system)

Authors: BETA Technological Centre (University of Vic Central University of Catalonia)
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