The project concerns the basic research into unsteady phenomena in gas-liquid multiphase systems typically occurring in bubble column contactors and reactors and aerated tanks. The goal is to understand the underlying mechanisms governing the bubble bed response to variations in the gas input: how the gas hold-up and flow regime are affected. These two are relevant for applications and design. We will try to understand the macroscopic behavior of bubbly layers from the point of view of interplaying small-scale phenomena: bubble size and speed, hydrodynamic bubble interactions in clusters. Further, the effect of viscosity and surface-active agents on dispersion behavior will be investigated.