Preliminary results on the relationship between chemical parameters and gasses emission in a PEC (photo-electrocatalytic) recirculating aquaculture systems for rainbow trout

The growing aquaculture raises significant environmental concerns. One potential adaptation strategy is recirculating aquaculture systems (RAS), a land-based solution that limits direct interaction with the environment. However, energy consumption and gaseous emissions are the main limiting factors for RAS. The Fish-photoCAT project (PRIMA), aims to evaluate the efficiency of a traditional RAS setup (mechanical-biofiltration + UV lamp) compared to an innovative solution based on photoelectrocatalysis (PEC). Previous studies showed that PEC avoids ammonia accumulation by converting it into gaseous nitrogen. The project's goals include estimating ammonia and greenhouse gas emissions. Analysed water samples are related to the second trial of the project, where the two RAS solutions, classical vs PEC, are investigated in Rainbow Trout fry (2g) reared at low density (5 kg/m³). Gasses emission flux was measured in laboratory conditions, using a static chamber, and the photoacoustic gas detector Innova 1512, was calculated according to the following formula [1]: F= S V A-1 [1] Where S is the regression slope (variation of gas concentration in time (mg m² h-¹), and V (m³) and A (m²) are respectively the volume and area of the chamber). Emissions correlations are established with water quality parameters, or nitrogen compounds, temperature, pH and oxygen saturation. Data were submitted to variance analysis, keeping the treatment as the main effect, and correlation analysis (SAS 9.4, 2023). During water sampling, tank conditions ranged from 15.7°C to 15.83°C in temperature; 7.65 to 8.03 in pH, and oxygen saturation from 80.7 % to 85 %. NH₃ was 0.18 mg/L vs 0.36 mg/L, NO₂ was 0.12 mg/L vs 0.26 mg/L, NO₃ was 8.9 mg/L vs 6.8 mg/L (P=0.06) respectively for the control and the PEC tanks. Gas emission factors from the control and the PEC tanks were 0.0716 mg m-² h-¹ vs 0.111.3 mg m-² h-¹ for NH₃, 0.0141 mg m-² h-¹ vs 0.1076 mg m-² h-¹ for N₂O, 1.98 mg m-² h-¹ vs 2.35 mg m-² h-¹ for CH₄ and 6.5 mg m-² h-¹ vs 13.3 mg m-² h-¹ for CO₂. Correlations revealed negative associations between NO₃ content and water temperature (r=-0.91, p<0.01), and N₂O emission flux and pH (r=-0.82; p<0.05), affected by fish number (p<0.001). CH₄ emission flux positively correlated (r=0.97, p<0.01) with CO₂ EF. Additional analysis is required to determine the effects and the efficiency of the proposed technology, other trials are “in fieri", for fry and adults at different rearing densities.