A descriptive study of carbon dioxide production and removal in full-scale RAS for Atlantic Salmon (Salmo salar L.) post-smolt: A comparison of two different measurement methods for CO2
Jafari, Leila; Fivelstad, Sveinung; Attramadal, Kari Johanne Kihle; Flataker, Håkon; Mjaatvedt, Pernille; Olsen, Anne Berit; Chierici, Melissa; Hosfeld, Anne-Camilla Diesen
Journal article, Peer reviewed
Published version
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https://hdl.handle.net/11250/3174796Utgivelsesdato
2024Metadata
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Sammendrag
Reliable data on metabolic rates and CO2 removal efficiency are essential for fish welfare in intensive production and RAS design. This descriptive study at a commercial post-smolt production facility evaluates two full-scale land-based RAS with different salinity levels: Module1 (M1) (2.5 ± 0.46‰ salinity) and Module2 (M2) (13.6 ± 0.46‰ salinity, with two separate RAS units, M2-RAS1, and M2-RAS2). Over eight weeks, water quality parameters were monitored in different places in the systems. CO2 concentrations were measured with an OxyGuard probe and calculated from total inorganic carbon (TIC). As fish biomass and feed load increased in both modules over time, CO2 concentrations increased and pH decreased, despite bicarbonate addition. In M1, CO2 levels increased from 6.2 to 16.4 mg L−1, while in M2, levels remained between 3.5 and 7.2 mg L−1. Apparent CO2 production, calculated from TIC, averaged at 5.2 ± 0.93 mg CO2 kg fish−1 min−1 in M1, and 3.2 ± 1.25 and 4.0 ± 1.45 mg CO2 kg fish−1 min−1 in M2-RAS1 and M2-RAS2 respectively. At the same time, the theoretical CO2 production rates showed a value of 4.4 ± 0.73, 4.2 ± 0.38, and 3.9 ± 0.71 mg CO2 kg fish−1 min−1 in M1, M2-RAS1, and M2-RAS2 respectively. The theoretical feed-to-CO2 conversion weight-to-weight ratio was estimated to be 0.345. However, M1 exhibited a higher measured feed-to-CO2 conversion ratio of 0.418, while M2-RAS1 and M2-RAS2 displayed ratios of 0.261 and 0.346, respectively. Observed CO2 (%) removal changed from 40% to 54% in M1, from 17% to 46% in M2-RAS1, and 26–44%, in M2-RAS2 over the observation period. This study suggests a significant role of the moving bed biofilter in CO2 removal, however, the effect size varied during the study and between modules, warranting further investigation. On average, 38% of CO2 removal before the degasser occurred within the biofilter in M1, and 49% in both RAS systems in M2. The total carbonate levels fluctuated over time, making it challenging to determine a clear increase or decrease, likely due to manual and varying bicarbonate additions. The two methods for assessing CO2 generally revealed minor differences and need more assessment. The prevalence of nephrocalcinosis was significantly more pronounced in M1 (73%), than in M2 (11%), which could be related to the difference in the CO2 level between the fish tanks. This study provides valuable insights into CO2 dynamics that may be useful in RAS design and operation for optimizing water quality and fish welfare.