A submersible aerator apparatus is disclosed. The apparatus uses injected air to create both aeration and mixing of a liquid. The apparatus is submersible and may be lowered into a container holding a liquid with suspended and coagulated solids, such as fats, oil, and grease (FOG). Air supplied to the apparatus is injected into the liquid through a hose, which results in an upward flow of large air bubbles and entrained liquid. The upwardly moving large air bubbles are cleaved (i.e., broken apart) by a series of baffle plates that are generally perpendicular to the direction of flow of the air bubbles. This action mixes and aerates the liquid.