Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The influence of design parameters (height and bed porosity) and operation parameters (liquid and gas superficial velocities) on the flow pattern of an up‐flow biological aerated filter has been studied. A lithium chloride pulse input was used for obtaining residence time distribution curves. Bed height was not found to influence the flow pattern but did increase retention time because of diffusion. Porosity was the controlling factor of the diffusional phenomena and, consequently, also controlled the hydrodynamic performance of the reactor. Thus, the flow pattern approximated more to plug‐flow and retention was greater in lower porosity filters (puzzolana bed) than in higher porosity units (sepiolite bed). The liquid velocity effect was more important than the gas velocity effect.</jats:p>