aerators are different from coarse bubble aerators, owing to their flow regime. The former has low interfacial gas velocities, hence induces low flow regimes at gas–liquid interfaces. Due to this flow regime (and the added decrease through scaling and fouling over time) the alpha factor (a, [9]) is substantially lower compared to 7the wide variety of aeration systems, leading to a lowered kLa. In contrast coarse-bubbles produce greater velocity gradients at the gas–liquid interface [8]. However the kLa of coarse bubble aerators is about six times smaller in contrast to the fine bubble KLa. Nonetheless when demanding an equal kLa, 3 times more diffusers are needed for fine bubble diffusers as these have the highest Ad, but demand a lower airflow rate, hence a higher power consumption (at 10 m tank depth +40%) [10]. Diffusers are still the most