Deoxygenation of Water for Small-Scale Laboratory Studies in Hydraulic Engineering

Achieving low dissolved oxygen levels in water is required for rigorous investigation of aeration processes in laboratory experiments in hydraulic engineering. The effectiveness of ultrasonic irradiation, vacuum degassing, water spraying techniques, and combinations thereof for deoxygenating tap water is evaluated in a closed-loop laboratory setting. A parametric study assessed the impact of ultrasonic irradiation (20 kHz, 2 kW), vacuum surface pressure (16–101 kPa), initial water temperature (11°C–39°C), and reservoir residence time (68–250 s) for flow rates in the range of 2.0–7.3 L/s. Results demonstrate that ultrasonic irradiation at 20 kHz did not significantly enhance the deoxygenation rate compared to vacuum degassing alone, suggesting that higher frequencies may be required to induce effective acoustic cavitation. Vacuum degassing effectively reduced dissolved oxygen levels, achieving a reduction from 10 down to 2.4 mg/L within 30 min at 16 kPa surface pressure and 33°C. Water spraying in a vacuum marginally improved deoxygenation at higher surface pressures by increasing the air–water interfacial area but became less effective at lower pressures due to increased surface mixing. Higher initial water temperatures and lower residence times had a minor influence on the deoxygenation rate. The results enable the design of deoxygenation systems suited for small-scale closed-loop hydraulic laboratories to establish well-controlled initial dissolved oxygen conditions.