Design and optimization of tubular oxygenation with pure oxygen for recirculating aquaculture systems

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ABSTRACT Objective To address the facility complexities and costs of existing oxygenation with pure oxygen, a tubular oxygenation device primarily composed of a diffused stone and PVC pipes was designed for recirculating aquaculture systems demanding high or even supersaturated levels of dissolved oxygen (DO). Methods Introducing pure oxygen into a diffused stone forms the oxygen-containing bubbles in the horizontal pipe with an outer diameter of 50 mm and a wall thickness of 3.5 mm. These bubbles are subsequently transferred into the vertical pipe with an enlarged diameter via a 90° elbow fitting. To improve oxygenation performance, the water inflow velocity and the vertical pipe were optimized using the oxygen increment rate and the oxygen utilization rate as indicators. Pure oxygen with a flow rate of 1.79 L/min generated from an oxygen generator and tap water at 11.3°C were adopted for the experiments. Results The concentration of DO and the oxygen increment rate were positively correlated with the outer diameter and the length of the vertical pipe, whereas they were negatively correlated with the water inflow velocity. The maximum DO was 21.29 mg/L and the oxygen increment rate was 78.73% at a water inflow velocity of 0.4 m/s through a vertical pipe with an outer diameter of 110 mm and a length of 40 cm. With the increase in the outer diameter and length of the vertical pipe, the oxygen utilization rate improved at the same water inflow velocity. Specifically, the oxygen utilization rate reached a peak of 15.87% at a water inflow velocity of 0.8 m/s through a vertical pipe with an outer diameter of 110 mm and a length of 40 cm. Conclusions The tubular oxygenation should accurately manage the water velocity in the vertical pipe. To achieve the better oxygen increment rate and oxygen utilization rate simultaneously, it is recommended to regulate the water inflow velocity to approximately 0.6 m/s by utilizing a vertical pipe with an outer diameter of 110 mm and a length of 40 cm. This study provides an alternative method of oxygenation with pure oxygen for recirculating aquaculture systems.