A fluid treatment apparatus comprises a fluid vessel defining first and second fluid chambers. A fluid inlet is provided for delivering a fluid to be treated into the first fluid chamber. One or more nozzle assemblies are provided for fluid communication between the first and second fluid chambers, wherein said nozzle assemblies are adapted to facilitate mixing of a gas with said fluid. The second fluid chamber is adapted to accommodate a fluid treatment process therein, including a floatation treatment. One specific use of the fluid treatment apparatus includes separating oil from water, particularly water produced from a subterranean formation.