Floatation separators separate hydrophobic particulates from hydrophilic particulates by passing fine air bubbles up through a solid-liquid mixture. The fine bubbles attach to and lift or float the hydrophobic particles up where they are collected. Floatation separator is used for primary treatment of waste streams with significant oil and grease loading or certain suspended or colloidal solids that are more amenable to separation and removal by floatation rather than by gravity settling.