Bubble-Water Surface and Turbulent Diffusion Mass Transfer in Fine Bubble Diffused Aeration Systems

Oxygenation efficiency has gained more and more attention in water bulk with a fine bubble aeration diffuser system operating. To enhance the oxygenation efficiency, one of the important researches is to explore the respective impact of different sources and the key factors on dissolved oxygen mass transfer, which will in turn be better for the design and operation of the fine bubble aeration diffuser system. A series of laboratory experiments for re-oxygenation were carried out in a glass tank, the fine bubble aeration diffusers were used to generate abundant fine air bubbles. There were two regions, i.e. the air bubbles and the non-bubbles zones in the experimented water bulk. According to the mass balance theory, the bubble-water surface mass transfer, turbulence diffusion mass transfer, global mass transfer and their oxygen utilization rates were achieved. The results showed that the values of oxygen volume mass transfer coefficient in air bubbles zone are smaller than the values of global oxygen volume mass transfer coefficient. The global oxygen utilization rate is greater than the oxygen utilization rate of bubble-water surface mass transfer. The impact of key factors on the global mass transfer are the bubble rise velocity, water velocity, submerged water depth, air flow rate, bubble diameter and water volume. The important factors improving aeration efficiency are the bubble rise velocity, bubble diameter and water velocity.