Potential of Opportunities for Reusing Sludge, Produced in Recirculating Aquaculture Systems

Aquaculture, just like any other economic activity, has effects on environment. This can be seen through the eutrophication and quality decrease of surrounding surface waters, due to being polluted by waste. One of the main advantages of recirculating aquaculture systems (RAS) is the absence of dispersed waste, i.e. the possibility to produce concentrated waste and thus simplify the decontamination process. This paper presents a review of RAS waste characteristics, global practices and tendencies of waste decontamination and their potential reuse, as well as recommendations, based on waste characteristics gathered through an analysis in an aquaculture farm. Sludge, produced in RAS, as well as the generated pollution, depends on the volume of feed. The main parameters, determining waste pollution – organic pollution index and dissolved nitrogen and phosphorus compounds - were measured in the analysed farm. The following results were obtained: biologic oxygen usage, showing the pollution of waste with organic material, was 106 mg/l, ammonium nitrogen concentration was 29 mg/l. This was significantly higher than 12 mg/l, found in literature. However, because the water pH index in the system oscillated between 6.27 and 6.7, in 230C water temperature; non-dissolved ammonium part was only 0.2%. Nitrite values were from 0.38 to 0.69 mg/, measured RAS phosphate values oscillated between 12 and 14 mg/l, which would correspond to phosphorus concentration of 3.9 – 4.6 mg/l. After determining the volume of sludge, produced in the RAS, relevant techniques for sludge reuse were suggested. The main features of these techniques are that they are eco-friendly, prevent pollution of surface water, are able to create added value and increase the profit of the companyVytauto Didžiojo universitetasŽemės ūkio akademij