A method for separating a biological suspension includes dispensing a liquid suspension comprised of cells or microorganisms from a bioreactor or fermenter into a sterile compartment of a first bag assembly, the first bag assembly including a collapsible bag having of one or more sheets of flexible film. The compartment of the first bag assembly is sealed closed. The first bag assembly, either with or without a manifold fluid coupled therewith, is then rotated, such as by using a centrifuge, so that the liquid suspension separates within the compartment into a pellet comprised of the cells or microorganisms and a liquid supernatant.