A centrifugal separator includes disposable cartridge having a cylindrical bowl, a core tube assembly, and an annular piston disposed around the core tube assembly and inside the inner surface of the bowl. The disposable cartridge may be automatically loaded and withdrawn from the separator. Feed liquid is injected down the core tube assembly into the lower portion of the bowl, raising the annular piston, while the bowl rotates at high speed, separating solids from the feed liquid to accumulate along the inner surface of the bowl, while collecting clarified centrate as it exits the top of the bowl and through the core tube assembly. In a solids discharge mode, the annular piston is urged downward along a vertical axis to force accumulated solids from the bowl.