Calculated analysis of oxygen transfer from air bubble-water interface and turbulent water surface in microporous aeration systems

Abstract: Micro porous aeration systems for increasing dissolved oxygen concentration in an aquaculture pond are receiving more and more attention. In order to explore the contribution of a micro bubble-water interface and the turbulent water surface to oxygen mass transfer, after placing a disc which was made of a curled micro porous diffuser tube in the middle bottom of an experimental pond, a series of re-oxygenation experiments were conducted under the conditions of different aeration flow and submerged water depth. Based on the theory of oxygen volume mass transfer, the calculation model recommended by the American Society of Civil Engineering (ASCE) was coupled with the Two-Zone oxygen transfer model, and then the two kinds of oxygen volume mass transfer coefficients across the micro bubble-water interface and across the turbulent water surface during the re-oxygenation process in the bottom of the experimental pond were calculated. After water temperature correction, the values of oxygen volume mass transfer coefficients across the micro bubble-water interface and across the turbulent water surface were found to be in a relationship with the aeration flow and submerged water depth of micro porous diffuser tube. Under a certain submerged depth of micro-porous tube, the bubble-zone volumetric mass transfer coefficients and the surface re-aeration-zone volumetric mass transfer coefficients are proportional to the diffused airflow rate. However, under a certain diffused airflow rate, the two zone mass transfer coefficients are inversely proportional to the water depth. For shallow aquaculture ponds, with the increase of submerged water depth of micro-porous tube, though the contribution of water surface to oxygen mass transfer has been weakened a little, however, the ratio of contribution on re-oxygenation still accounts for more than 80%. Combining micro porous aeration systems has the advantage of low energy consumption and simple installation, using the micro porous diffuser system to increase dissolved oxygen concentration and water turbulent mixing in shallow water has a greater advantage, and is worth popularizing.