A hollow-fiber membrane device is operated to concentrate a bacterial suspension. The flow rate of cell suspension into the fibers is 350 kg/min. The inlet cell suspension is comprised of 1.0 wt% bacteria; the rest of the suspension can be considered water. An aqueous buffer solution enters the annular space at a flow rate of 80.0 kg/min. Because the cell suspension in the membrane tubes is under pressure, water is forced from the tubes, across the membrane, and into the buffer. Bacteria in the cell suspension are too large to pass through the membrane, and thus they remain in the membrane tubes throughout the device. The outlet cell suspension is comprised of 6.0 wt% bacteria. Assume that the cells do not grow. Also assume that the membrane does not allow any molecules other than water to pass across it.

Determine the mass flow rates of the outlet cell suspension stream and the outlet buffer stream.

Determine the mass flow rate of the water across the membrane.
 

Outlet Inlet Outlet Inlet