Which solids treatment method aerates the recycled water from the unit under pressure?

The solids treatment method that involves aerating recycled water from the unit under pressure is flotation thickening. This process utilizes the physical principle of flotation, where fine air bubbles are introduced into a mixture of water and solids under pressure. The bubbles attach to the solids, causing them to rise to the surface, forming a layer of concentrated solids or sludge. This not only helps in separating the solids from the liquid but also allows for the aeration of the recycled water, improving its quality and facilitating further treatment or reuse.

In contrast, gravity thickening relies on the natural gravitational settling of solids without the use of additional pressure or aeration. Composting and lime stabilization are both processes intended for the treatment of biosolids but do not involve aeration of recycled water under pressure. Composting focuses on organic degradation at specific temperatures, while lime stabilization aims to raise pH levels to further stabilize the sludge. Thus, flotation thickening stands out as the method that aerates recycled water through pressure.