Optimizing oxygen dissolution in water with microbubble flow

Sustaining a specific level of oxygen in water is critical for aquatic organisms.Many factors can affect the dissolution process of oxygen and ultimately its required concentration.The influence of temperature, flow rate, pH, and turbidity on the oxygen gas content and its mass transfer coefficient through water in a micro-bubble column has been investigated.The tested temperatures were 7, 13, 16, 25, and 30 1 C, the flow rates of oxygen gas were 0.5, 1, and 1.5 L min -1 , the pH values were 4, 7, and 10, and turbidity of 0.2, 35, 65, and 95 NTU.Compressed air was bubbled into the distilled water column via a ceramic diffuser (Point Four microbubble diffuser) with the most frequent bubble size of 300-400 m.The oxygen concentration was monitored online every 1 minute via an oxygen meter.The results demonstrate that the oxygen content increases with time at each temperature and its saturated concentration oscillates around 7 minutes of the oxygenation process.The greatest O 2 concentrations in pure water (0.2 NTU) measured at flow rate of 0.5 L min -1 and pH 7 were 16.5, 15, 14.5, 12, and 11 ppm as corresponded with the particular related temperatures.Increasing the flow rate to 1 and 1.5 L min -1 at constant temperature of 16 C enhanced earlier saturation to only 4 min and increased the mass transfer coefficient (K La ) to 2.3 and 2.7 10 -2 s -1 respectively, comparing with 1.23 10 -2 s -1 at 0.5 L min -1 .However, the oxygen concentration at equilibrium was not considerably changed.The data of turbidity effect showed decreasing of dissolved oxygen and the K La by less than 10% after increasing turbidity to 95 NTU.Without generating micro-bubbles, the oxygen content of the pure water (0.2 NTU) was around 6 ppm and the K La of about 0.94 10 -2 s -1 at 16 C, pH 7, flow of 0.5 L min -1 , and turbidity 0.2 NTU, indicating the effectiveness of the micro-bubble flow scenario.