Bubbly flows are encountered in a variety of industrial and environmental applications and their properties in terms of separation process, mixing and aeration are particularly beneficial in waste water treatment. Aeration or oxygenation of waste water aims at providing oxygen to micro-organisms to consume biodegradable materials and typically accounts for 50 to 90% of the energy consumption of waste water treatment plants. Despite a number of technologies available, current methods still suffer from a poor efficiency and it is common for a treatment plant that 75% of the oxygen injected in an aeration tank is released at the surface instead of being transferred to the water.
Microbubbles provide several advantages for aeration applications, including high interfacial area to volume ratio and long residence time. Experiments have been performed in DCU with aqueous solutions to investigate oxygen transfer under a wide range of operating conditions and levels of interface contamination. Complementary tests on a waste water treatment site, in partnership with ABP Food Group, are also being performed with their current aeration system and a Navier-Stokes flow solver based on OpenFOAM libraries with a lagrangian representation of the bubbles is also being used to gain further insight on oxygen transfer mechanisms. Oxygen transfer efficiencies are estimated as a function of operating conditions and the physico-chemical parameters influencing the contributions to mass transfer are assessed.