Energy use in Recirculating Aquaculture Systems (RAS) – A review 2013
Recirculating aquaculture systems (RAS) are increasingly being used for Atlantic salmon smolt produc- tion. However, knowledge of how the RAS environment affects welfare and performance of Atlantic salmon is limited. For instance, safe limits for chronic exposure to typical compounds in RAS, such as NH3-N, NO2-N, and CO2 should be established for Atlantic salmon, as well as their interactions with nutrition, other RAS water compounds, and the microbiota. These questions can best be answered in a research facility that is providing a RAS environment. In addition, the facility described here was required to produce 480 000 smolts annually, to provide sufficient research fish in the institution. Design and dimensioning of such a facility require attention to flexibility for various experimental designs, and the flexibility to vary specific water quality constituents, properties that are not necessary in a standard production plant. A research facility of 1754 m2 ground floor area (Nofima Centre for Recirculation in Aquaculture, NCRA), was designed and constructed for these purposes at a cost of 45 mill. NOK (2010 value). The facility included six experimental halls, a number of support rooms, and four independent RASs. Water quality requirements at maximum feed loading were in the design phase set to <10 mg/L CO2, <0.7–1 mg/L TAN, and <0.1 mg/L NO2-N, and the RASs dimensioned with this objective. The facility was designed so that water from different RAS or flow-through water sources could be chosen atthe level of the culture tanks, thus giving flexibility for experimentation. Performance of the facility was tested in two trials, during the first 3 years of operation. In Trial 1, a standard production study showed that Atlantic salmon parr reared in the facility had growth rates comparable to that seen in the Norwegian Atlantic salmon smolt industry. In Trial 2, water quality and removal efficiencies of RAS 1 were evalu-ated at increasing daily feed loads. Removal efficiencies were comparable, in the case of TAN, and when calculated for the system as a whole also for CO2, to assumptions made during dimensioning and design of the facility. The RAS maintained water quality within set limits for TAN and CO2, but not in the case of nitrite (0.22 mg/L NO2-N versus 0.1 mg/L limit). The water quality limits of TAN and CO2 were reached, not at full feed capacity, but at 134% of the theoretical feed capacity calculated prior to construction. This dimensioning was based on an often used methodology. When recalculating the RAS 1 TAN production, but now using published Atlantic salmon parr N-retention data, it was found that the methodology used prior to construction may over-estimate the TAN production by about 34%. Thus, Trial 2 was useful for recalibrating the feed load capacity of the RASs, and for accurate experimental design in future projects. It is expected that in the long-term NCRA will be useful in determining the environmental and nutritional requirements of fish reared in RAS.
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