Bubbly flows in Chemical Engineering systems are typically accompanied by transfer of chemical components from one phase to the other, often followed by chemical reaction. CFD models such as the Euler-Euler or the Euler-Lagrange model require the modelling of closure terms which account for the exchange of mass, momentum, species mass etc. between the phases. This requires a detailed understanding of the hydrodynamics and mass transfer especially at single bubbles. Here, Direct Numerical Simulations based on the continuum mechanical models have recently become a helpful complement to the experimental investigations needed for the derivation of such closures terms. This paper reports on current numerical approaches for the Direct Numerical Simulation of single bubble dynamics both in a clean liquid and in a surfactant solution, as well as on reactive mass transfer at a rising bubble.