An embodiment of a screw press separator for separating a slurry containing solid and liquid components has a housing and a cylindrical screen, which is arranged in the housing and on which a longitudinal direction and a circumferential direction are defined. The screen is rotatable about the longitudinal direction. The separator also includes a screw arranged inside the screen for pressing out the slurry, the screw being rotatable about the longitudinal direction, at least one retaining element arranged in the housing, at least one actuator adapted to move the at least one retaining element between a locking position and a freewheeling position, and at least one stop connected to the screen. The separator is configured so that the screen is rotationally fixed in at least a circumferential direction in the locking position and the screen co-rotates with the screw in the freewheeling position.