Abstract: A particle separating apparatus for fluids containing particulate material, treatment system for treating effluent from a processing plant, and a method of separating particles from fluid. A treatment vessel has an inlet for injecting fluid containing particulate material, and a plurality of outlets for separately discharging separated supernatant on the one hand, and separated particles on the other hand, from the fluid. An outer annular treatment region receives fluid injected tangentially into said treatment vessel from the inlet and directs the fluid into a transverse, laminar flow within the vessel about a central axis. An inner particle separating region communicates with the outer treatment region but is separated therefrom by a baffle to permit ingress of the injected fluid gradually from the transverse flow in a radially converging manner that maintains the laminar flow for fluid.