A fluid flow circuit assembly in the form of a molded, disposable cassette for a blood processing device, comprising a housing having a plurality of openings, a spinning membrane separator disposed at least partially within the housing, and a plurality of flow paths communicating between an interior and an exterior of the housing via the plurality of openings, wherein the separator is disposed substantially at the center of the plurality of flow paths. The cassette can be loaded onto a loading platform of a blood processing device. The loading platform comprises a separator drive motor configured to engage the spinning membrane separator and is capable of translational motion to automatically load the cassette onto pumps on the blood processing device.
