In the Folded Flow® design, as the density current travels laterally, clean water, being heavier, peels away from the bottom of the density current and flows downward. At the bottom of the tank, the downward flow gathers in a laminar fashion to form a horizontal return current, which accelerates as it nears the outlet. The downward velocity of liquid from the surface layer to the return stream at the bottom is relatively constant along the length of the tank and is uniformly close to a minimum flow. This ensures that the bubbles are moving upward throughout the entire volume of the tank.