Experimental Study On The Mechanism Of Fine Bubble Diffused Aeration System In The Bottom Of Aquaculture Pond

With the aquaculture industry continueing to heat up, the stocking density increasing, and the techniques to get high yield and high efficiency being popularized, the aeration equipments are more and more becoming essential equipment in aquaculture ponds. Fine bubble aeration systems(FBAS) belonging to aeration systems has been widely used in aquaculture ponds to increase dissolved oxygen(DO) concentration and promote water circulation. This is because its aeration efficiency is higher and suitability is much stronger. However, its absolute value of oxygen efficiency and power efficiency is not high. The main reasons are that,(1) The researches just considered the internal water oxygen mass transfer, without taking into account the oxygen mass transfer produced by the water surface disturbance in aquaculture ponds recently.(2) Most researchers ignored the division of the air bubbles zone and the non-bubbles zone, and thought that the mass transfer across the interfaces of air bubbles and water free surface made entire contribution to the DO concentration in the whole area of aeration pond, no matter in the air bubbles zone or in the non-bubbles zone, causing that a very important form of oxygen mass transfer is ignored.(3) Most studies just studied the impact of water depth, aeration flow rate, bubble size, etc on aeration efficiency, but not considered the effect of aeration tube length on aeration efficiency, meanwhile, not made a detailed study for the key factors of aeration efficiency.(4) The installation interval of two aerators is still in a blank state, with the so-called experience and blindness to carry out installation, increasing the more waste of energy.(5) We lack of the prediction model of the global volumetric mass transfer coefficient and oxygen utilization to predict their values.The above problems will be solved by using the following methods in this study,(1) There are internal water oxygen mass transfer and water surface oxygen mass transfer in the atmosphere and water, meanwhile, there are air bubble-water interface mass transfer and turbulent diffusion mass transfer in the water body.(2) The effect of aeration flow rate and aeration tube on the global volumetric mass transfer and oxygen utilization will be studied, and the model of the optimal aeration tube length will be built.(3) The model of the best installation interval of two aerators and global volumetric mass transfer and oxygen utilization will be established.The a series of laboratory tests will be conducted in this paper. The result shows that, for this shallow-water area type of aquaculture ponds,(1) The rate of water surface mass transfer to global mass transfer is greater than 80%, however, the contribution of water surface mass transfer to global mass transfer is not large. The turbulent diffusion mass transfer and air bubble-water interface mass transfer contributed to DO are not very different.(2) The key factors are rising velocity of bubbles, bubble diameter, water velocity, aeration flow rate, submerged water depth, water volume to improve the global mass transfer and aeration efficiency.(3) The aeration tube length makes the global volumetric oxygen mass transfer coefficient and oxygen utilization changing a lot, mainly for the first low to high and then low to high tendency.(4) The established models of optimal aeration tube length, optimal installation spacing, global volumetric oxygen mass transfer coefficient and oxygen utilization are in good agreement with the measured values, which can provide valuable reference for practical applications.