A system for separating phases of a liquid stream, comprising a plurality of members each member having an inlet and an outlet such that the outlet of one member is connected to the inlet of another with members being horizontally or vertically stacked in relation to each other. Each member comprises: a container for holding liquid to be treated; a vessel for receiving the liquid stream from the container; a first means in communication with the vessel at one point for selectively introducing into the vessel a gaseous body; a second means in communication with the vessel positioned downstream of first means for selectively introducing into the vessel a liquid stream and for advancing the gaseous body through the vessel at a selectable rate, a power means for motivating both first and second means, an impeller means positioned at one end of the power means and within the vessel for mechanically agitating the liquid stream in order to urge the gaseous body into combination with the liquid stream and a vacuum initiating means within the vessel and upstream of the impeller means.