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. The fluid eventually reposes centrally of the treatment vessel for optimum residency in the inner particle separating region. The baffle mitigates the effects of the angular fluid motion in the outer annular treatment region on fluid within the inner separating region. A lower particle collection region communicates with both the lower portion of the outer treatment region and said inner particle separating region for receiving separated particles from the fluid having a higher specific gravity. An upper supernatant separating region communicates with the top of the inner particle separating region for egressing supernatant from the fluid for extraction. The baffle has a recess opening from the depending thereof behind the inlet and spanning a sector of approximately 90 DEG .